ALBERT

Notes: Many plants accumulate organic osmolytes in response to the imposition of environmental stresses that cause cellular dehydration. Although an adaptive role for these compounds in mediating osmotic adjustment and protecting subcellular structure has become a central dogma in stress physiology, the evidence in favour of this hypothesis is largely correlative. Transgenic plants engineered to accumulate proline, mannitol, fructans, trehalose, glycine betaine or ononitol exhibit marginal improvements in salt and/or drought tolerance. While these studies do not dismiss causative relationships between osmolyte levels and stress tolerance, the absolute osmolyte concentrations in these plants are unlikely to mediate osmotic adjustment. Metabolic benefits of osmolyte accumulation may augment the classically accepted roles of these compounds. In re-assessing the functional significance of compatible solute accumulation, it is suggested that proline and glycine betaine synthesis may buffer cellular redox potential. Disturbances in hexose sensing in transgenic plants engineered to produce trehalose, fructans or mannitol may be an important contributory factor to the stress-tolerant phenotypes observed. Associated effects on photoassimilate allocation between root and shoot tissues may also be involved. Whether or not osmolyte transport between subcellular compartments or different organs represents a bottleneck that limits stress tolerance at the whole-plant level is presently unclear. None the less, if osmolyte metabolism impinges on hexose or redox signalling, then it may be important in long-range signal transmission throughout the plant.

Notes: The evergreen species Yucca glauca was characterized at the end of September and following exposure to low temperatures at the end of November. In November the diurnal pattern of xanthophyll cycle-dependent energy dissipation was altered such that this thermal dissipation process was engaged at a high level throughout the day, whereas in September it only became engaged when leaves received direct sunlight. An analysis of the diurnal partitioning of the absorbed excitation energy into photochemistry versus thermal dissipation suggested that a smaller fraction of that energy was utilized in photochemistry and a greater fraction was dissipated thermally at the end of November compared to September. Lower ratios of Chl a/b and β-carotene/xanthophylls both suggested a decrease in the ratio of reaction centre plus core antenna proteins compared to light-harvesting proteins, and a lower leaf chlorophyll content suggested a decrease in light-harvesting capacity in November versus September. Thus adjustments to the photosynthetic apparatus occurred on several levels in response to the increase in excess excitation energy that Y. glauca experienced during the onset of winter.

Notes: Variations in the water relations and stomatal response of Quercus ilex were analysed under field conditions by comparing trees at two locations in a Mediterranean environment during two consecutive summers (1993 and 1994). We used the heat-pulse velocity technique to estimate transpirational water use of trees during a 5 month period from June to November 1994. At the end of sap flow measurements, the trees were harvested, and the foliage and sapwood area measured. A distinct environmental gradient exists between the two sites with higher atmospheric CO2 concentrations in the proximity of a natural CO2 spring. Trees at the spring site have been growing for generations in elevated atmospheric CO2 concentrations. At both sites, maximum leaf conductance was related to predawn shoot water potential. The effects of water deficits on water relations and whole-plant transpiration during the summer drought were severe. Leaf conductance and water potential recovered after major rainfall in September to predrought values. Sap flow, leaf conductance and predawn water potential decreased in parallel with increases in hydraulic resistance, reaching a minimum in mid-summer. These relationships are in agreement with the hypothesis of the stomatal control of transpiration to prevent desiccation damage but also to avoid ‘runaway embolism’. Trees at the CO2 spring underwent less reduction in hydraulic resistance for a given value of predawn water potential. The decrease in leaf conductance caused by elevated CO2 was limited and tended to be less at high than at low atmospheric vapour pressure deficit. Mean (and diurnal) sap flux were consistently higher in the control site trees than in the CO2 spring trees. The degree of reduction in water use between the two sites varied among the summer periods. The control site trees had consistently higher sap flow at corresponding values of either sapwood cross-sectional area or foliage area. Larger trees displayed smaller differences than smaller trees, between the control and the CO2 spring trees. A strong association between foliage area and sapwood cross-sectional area was found in both the control and the CO2 spring trees, the latter supporting a smaller foliage area at the corresponding sapwood stem cross-sectional area. The specific leaf area (SLA) of the foliage was not influenced by site. The results are discussed in terms of the effects of elevated CO2 on plant water use at the organ and whole-tree scale.

Notes: Water relations of tomato fruit and the epidermal and pericarp activities of the putative cell wall loosening and tightening enzymes Xyloglucan endotransglycosylase (XET) and peroxidase were investigated, to determine whether tomato fruit growth is principally regulated in the epidermis or pericarp. Analysis of the fruit water relations and observation of the pattern of expansion of tomato fruit slices in vitro, has shown that the pericarp exerts tissue pressure on the epidermis in tomato fruit, suggesting that the rate of growth of tomato fruit is determined by the physical properties of the epidermal cell walls. The epidermal activities of XET and peroxidase were assayed throughout fruit development. Temporal changes in these enzyme activities were found to correspond well with putative cell wall loosening and stiffening during fruit development. XET activity was found to be proportional to the relative expansion rate of the fruit until growth ceased, and a peroxidase activity weakly bound to the epidermal cell wall appeared shortly before cessation of fruit expansion. No equivalent peroxidase activity was detected in pericarp tissue of any age. It is therefore plausible that the expansion of tomato fruit is regulated by the combined action of these enzyme activities in the fruit epidermis.

Notes: We explore the extent to which a simple mechanistic model of short-term plant carbon (C) dynamics can account for a number of generally observed plant phenomena. For an individual, fully expanded leaf, the model predicts that the fast-turnover labile C, starch and protein pools are driven into an approximate or moving steady state that is proportional to the average leaf absorbed irradiance on a time-scale of days to weeks, even under realistic variable light conditions, in qualitative agreement with general patterns of leaf acclimation to light observed both temporally within the growing season and spatially within plant canopies. When the fast-turnover pools throughout the whole plant (including stems and roots) also follow this moving steady state, the model predicts that the time-averaged whole-plant net primary productivity is proportional to the time-averaged canopy absorbed irradiance and to gross canopy photosynthesis, and thus suggests a mechanistic explanation of the observed approximate constancy of plant light-use efficiency (LUE) and carbon-use efficiency. Under variable light conditions, the fast-turnover pool sizes and the LUE are predicted to depend negatively on the coefficient of variation of irradiance. We also show that the LUE has a maximum with respect to the fraction of leaf labile C allocated to leaf protein synthesis (alp), reflecting a trade-off between leaf photosynthesis and leaf respiration. The optimal value of alp is predicted to decrease at elevated [CO2]a, suggesting an adaptive interpretation of leaf acclimation to CO2. The model therefore brings together a number of empirical observations within a common mechanistic framework.

Notes: To assess the possible physiological function of chlorogenic acid (CGA, 3-O-caffeoylquinic acid) in vivo, we characterized the free radical scavenging properties of pure phenylpropanoids and leaf extracts against two free radicals, superoxide and the 2,2’-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical cation. CGA was found to be a highly efficient scavenger of these free radicals, surpassing the activity of all other phenylpropanoids tested, as well as the ‘classical’ antioxidant ascorbate. Seasonal differences in the leaf content of CGA were examined in field populations of the broadleaf evergreen Mahonia repens growing in different light environments. Leaves of fully sun-exposed plants contained significantly more (74 ± 10 mmol m–2) CGA in winter than leaves from plants growing under deeply shaded conditions (17 ± 2 mmol m–2). Sun-acclimated, but not shade-acclimated, leaves also produced high levels of anthocyanins in winter, suggesting a simultaneous increase in carbon flow through the phenylpropanoid and flavonoid pathways in response to high light and seasonal low temperature stress. In summer, high light-acclimated leaves contained ≈ 2-fold less CGA than in winter, whereas CGA levels were similar between seasons in shaded leaves. Consistent with the strong scavenging capacity of CGA measured in vitro, a linear correlation was observed between CGA content and the antioxidant activity of leaf extracts in both scavenging assays. On the basis of these results, we propose that CGA is a powerful hydrogen-donating antioxidant that may play an important role in mitigating the effects of oxidative stress in plants.

Notes: Pulses of blue light cause stimulation of red light saturated photosynthesis in Ectocarpus siliculosus, because blue light activates the operation of a pathway for inorganic carbon (Ci) acquisition by inducing the mobilization of CO2 from an intermediate metabolite. In the absence of exogenous Ci, photosynthetic rates roughly equal those of CO2 release by respiration. In seawater of pH 9·5 (2·3 mol m–3 total Ci, but concentrations of free CO2 below 0·2 mmol m–3), photosynthesis was clearly above these rates, although they were only ≈ 30% of those in normal seawater (≈ pH 8). The degree and the time course of the stimulations of photosynthesis by pulses of blue light were unaltered at high pH. Essentially the same characteristics were found after buffering or in the presence of acetazolamide, an inhibitor of extracellular carbonic anhydrase activity. Therefore, it is concluded that Ectocarpus is able to directly take up HCO3– in addition to CO2 (uptake of CO32– cannot be excluded). The dependence of photosynthesis on Ci at pH 9·5 was biphasic, with Ci below 0·2 mol m–3 having no effect at all. In Ci-free seawater, the shapes of the stimulations after blue light pulses differed for pH 6, pH 8 and pH 9·5. At low pH, only the fast peak (maximum ≈ 5 min after blue light) was detected, whereas at high pH mainly the slow peak (maximum ≈ 20 min after blue light) was observed. At the intermediate pH 8, both peaks were present. As inhibition of total carbonic anhydrase by ethoxyzolamide brought out the fast peak of the stimulations at pH 9·5 it is concluded that the fast component was due to a transient disequilibrium of an intracellular pool of Ci which, after blue light, was fed by CO2 released from the postulated storage intermediate.

Notes: The combined effects of carbon dioxide (CO2) enrichment and water deficits on nodulation and N2 fixation were analysed in soybean [Glycine max (L.) Merr.]. Two short-term experiments were conducted in greenhouses with plants subjected to soil drying, while exposed to CO2 atmospheres of either 360 or 700 μmol CO2 mol–1. Under drought-stressed conditions, elevated [CO2] resulted in a delay in the decrease in N2 fixation rates associated with drying of the soil used in these experiments. The elevated [CO2] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO2]. The total non-structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought; however, plants under elevated CO2 had much higher TNC levels than those under ambient CO2. For both [CO2] treatments, drought stress induced a substantial accumulation of TNC in the nodules that paralleled N2 fixation decline, which indicates that nodule activity under drought may not be carbon limited. Under drought stress, ureide concentration increased in all plant tissues. However, exposure to elevated [CO2] resulted in substantially less drought-induced ureide accumulation in leaf and petiole tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO2] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N2 rates under soil water deficits. We suggest that future [CO2] increases are likely to benefit soybean production by increasing the drought tolerance of N2 fixation.

Notes: The aim of the present study was to test the four commonly used models to predict the dates of flowering of temperate-zone trees, the spring warming, sequential, parallel and alternating models. Previous studies concerning the performance of these models have shown that they were unable to make accurate predictions based on external data. One of the reasons for such inaccuracy may be wrong estimations of the parameters of each model due to the non-convergence of the optimization algorithm towards their maximum likelihood. We proposed to fit these four models using a simulated annealing method which is known to avoid local extrema of any kind of function, and thus is particularly well adapted to fit budburst models, as their likelihood function presents many local maxima. We tested this method using a phenological dataset deduced from aeropalynological data. Annual pollen spectra were used to estimate the dates of flowering of the populations around the sampling station. The results show that simulated annealing provides a better fit than traditional methods. Despite this improvement, classical models still failed to predict external data. We expect the simulated annealing method to allow reliable comparisons among models, leading to a selection of biologically relevant ones.

Notes: Carbon isotope composition (δ13C) was measured in a glasshouse experiment with N2-fixing and NO3–- or NH4+-fed Casuarina equisetifolia Forst. & Forst plants, both under well-watered and drought conditions. The abundance of 13C was higher (more positive δ13C) for NH4+- than for NO3– -grown plants and was lowest for N2-fixing plants. NH4+-fed plants had more leaf area and dry weight and higher water use efficiency (on a biomass basis) than N2- and NO3–-grown plants and had lower water consumption than plants supplied with NO3–, either with high or low water supply. Specific leaf areas and leaf area ratios were higher with NH4+ than with NO3– or N2 as the N source. The difference observed in δ13C between plants grown with different N sources was higher than that predicted by theory and was not in the right direction (NH4+-grown plants with a more negative δ13C) to be explained by differences in plant composition and engagement of the various carboxylation reactions. The more positive δ13C in NH4+- than in NO3–-grown plants is probably due to a decreased ratio of stomatal to carboxylation conductances, which accounts for the lower water cost of C assimilation in NH4+-grown plants.

Notes: Growth under elevated [CO2] promoted spring frost damage in field grown seedlings of snow gum (Eucalyptus pauciflora Sieb. ex Spreng.), one of the most frost tolerant of eucalypts. Freezing began in the leaf midvein, consistent with it being a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO2] (– 5·7 °C versus – 4·3 °C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO2 fertilization and may affect predictions of vegetation change based on increasing temperature.

Notes: The objective of this investigation was to examine the effect of an elevated atmospheric CO2 partial pressure (pCO2) on the N-sink strength and performance of symbiotic N2 fixation in Trifolium repens L. cv. Milkanova. After initial growth under ambient pCO2 in a nitrogen-free nutrient solution, T. repens in the exponential growth stage was exposed to ambient and elevated pCO2 (35 and 60 Pa) and two levels of mineral N (N-free and 7·5 mol m–3 N) for 36 d in single pots filled with silica sand in growth chambers. Elevated pCO2 evoked a significant increase in biomass production from day 12 after the start of CO2 enrichment. For plants supplied with 7·5 mol m–3 N, the relative contribution of symbiotically fixed N (%Nsym) as opposed to N assimilated from mineral sources (15N-isotope-dilution method), dropped to 40%. However, in the presence of this high level of mineral N, %Nsym was unaffected by atmospheric pCO2 over the entire experimental period. In plants fully dependent on N2 fixation, the increase in N yield reflects a stimulation of symbiotic N2 fixation that was the result of the formation of more nodules rather than of higher specific N2 fixation. These results are discussed with regard to physiological processes governing symbiotic N2 fixation and to the response of symbiotic N2 fixation to elevated pCO2 in field-grown T. repens.

Notes: Tobacco seedlings were grown in nutrient agar at a range of ammonium nitrate concentrations either without added sucrose, or with 100 mol m–3 sucrose. In the absence of added sucrose, nitrogen-limited plants had increased levels of glucose, fructose and sucrose, decreased chlorophyll, decreased protein, and decreased Rubisco activity, but the level of the transcript for the small subunit of Rubisco (RbcS) did not decrease compared with nitrogen-sufficient plants. When sucrose was added to nitrogen-sufficient seedlings, there was an increase of sucrose, glucose and fructose in the leaves, growth was increased, and the chlorophyll and protein content, Rubisco activity, and the RbcS transcript level did not change. When sucrose was added to nitrogen-limited seedlings, there was a further increase of sucrose, glucose and fructose, growth was not increased, and there was a further decrease of chlorophyll, protein and Rubisco activity, and a marked decrease of the RbcS transcript level. To check that the decrease of the RbcS transcript level was not an indirect effect due to changes of nitrogen metabolites after adding sugars, glucose was added to Chenopodium cells in the presence and absence of glutamine or azaserine. Changes of glutamine that suffice to increase and decrease the level of the transcript for nitrate reductase (Nia) do not affect the RbcS transcript concentration, and glucose addition still led to a decrease of the RbcS transcript level when the internal glutamine concentration was high. Tobacco seedlings were also grown in nutrient agar at a range of phosphate concentrations either without added sucrose, or with 100 mol m–3 sucrose. Phosphate-limited seedlings did not show a decrease of chlorophyll, protein, Rubisco activity, or the level of the RbcS transcript, compared with phosphate-sufficient seedlings. The addition of sucrose to phosphate-limited plants led to a similar increase of sugars to that seen after adding sucrose to nitrogen-limited seedlings, but did not alter chlorophyll, protein, Rubisco activity, or the level of the RbcS transcript. The addition of sucrose to phosphate-limited plants led to a slight increase of the level of the transcript for nitrate reductase (Nia), increased nitrate reductase activity, and a marked increase of the amino acid content. Phosphate limitation led to an increased level of the transcript for the regulatory subunit of ADP glucose pyrophosphorylase (AgpS2), and this response was strengthened when sucrose was added. The regulation of AgpS2 expression by phosphate and sucrose was further investigated by feeding sucrose and phosphate to detached source leaves via the transpiration stream. The level of the AgpS2 transcript decreased after feeding phosphate and increased after feeding sucrose, and the effect of sucrose was antagonised by phosphate. It is concluded that the response to sugar signalling is modulated by nitrogen and phosphate in a gene-specific manner. The significance of these results for understanding the visual phenotype of nitrogen- and phosphate-limited plants, and the response of photosynthesis and starch synthesis to the plant nutrient status is discussed.

Notes: In many woody plants a short photoperiod triggers the onset of cold acclimation, but the nature of this process has remained obscure. We aimed to establish which physiological and genetic factors have a role in short-day-induced acclimation by comparing two types of birch, Betula pubescens Ehrh. and B. pubescens f. hibernifolia Ulv., the latter being unable to increase its abscisic acid (ABA) levels. In the wild type, short-day or natural autumn conditions in the field appeared to elevate the ABA levels before acclimation, which was accompanied by tissue desiccation, osmotic adjustments and accumulation of Group 2 LEA proteins [responsive to ABA (RAB) 16-like; 24, 30 and 33 kDa] and Group 4 LEA proteins [late embryogenesis abundant (LEA) 14-like; 19 kDa]. Under similar conditions the ABA-deficient birch showed reduced water loss, defective osmoregulation, absence of inducible Group 2 LEA proteins, and delayed or reduced tolerance to freezing. In contrast, both birch genotypes showed similar seasonal production patterns of Group 4 LEA proteins. Our results demonstrate that onset of cold acclimation in birch is based on multiple mechanisms, including molecular pathways that are typical of stress responses. ABA may be important for the accurate timing of cold acclimation in trees that are sensitive to photoperiod.

Notes: Tadmor is a Syrian barley landrace that has adapted to semi-arid environments. Its leaves are pale green because of a 30% decrease in the chlorophyll and the carotenoid content of the chloroplasts (leading to a 7·5% decrease in light absorption) compared with barley genotypes that are not adapted to harsh Mediterranean climatic conditions (e.g. Plaisant). This difference in pigment content was attenuated during growth of the plants in strong light, but was strongly amplified when strong light was combined with a high growth temperature. The low pigment content of Tadmor leaves was not associated with significant changes in the pigment distribution between the photosystems or between the reaction centres of the photosystems and their associated chlorophyll antennae. No significant difference in the photosynthetic activity (O2 production per unit absorbed light) was observed between Tadmor and Plaisant. The conversion of violaxanthin to zeaxanthin in strong light and its reversal in darkness were much faster and operated at a higher capacity in Tadmor leaves compared with Plaisant leaves, resulting in an increased photostability of photosystem II in the former leaves. The accelerated xanthophylls interconversion in the Syrian landrace was associated with, and possibly related to, an increased fluidity of the thylakoid membranes. The lipid peroxide level was lower in Tadmor compared with Plaisant. In contrast, no difference was found in the non-photochemical quenching of chlorophyll fluorescence between the two barley genotypes. The data indicate that the pale green Syrian landrace is equipped to survive excessive irradiance through a passive reduction of the light absorptance of its leaves, which mitigates the heating effects of strong light, and through the active protection of its photochemical apparatus by a rapid xanthophyll cycling.

Notes: A mechanistic model has been used to examine the environmental regulation of photosynthetic gas exchange in moss. The effects of water content on conductance to CO2 and on photosynthetic capacity during desiccation were calculated from the carbon isotope discrimination data of Williams & Flanagan (1996, Oecologia 108, pp. 38–46) and combined with the biochemical model of Farquhar et al. (1980, Planta 149, pp. 78–90). The model includes a simple light attenuation function that imparts curvature to the light response curve for net assimilation, enabling the use of physiologically realistic values for the biochemical parameters. Measurements of gas exchange for Sphagnum and Pleurozium were made in an old black spruce ecosystem over a growing season in order to assign values to parameters in the model. The calculated maximum rates of carboxylation by Rubisco (Vmax) were 5, 14 and 6μmol m–2 s–1 for Sphagnum during the spring, summer and autumn seasons of 1996, respectively. The increase in Vmax during the summer was consistent with an increased allocation of resources to the photosynthetic apparatus. In contrast, no seasonal variation in Vmax was observed in Pleurozium with average values of 7, 5 and 7 μmol m–2 s–1 during the spring, summer and autumn, respectively.

Notes: We investigated variation in intrinsic water-use efficiency during the past century by analysing δ13C in tree rings of beech growing in north-eastern France. Two different silvicultural systems were studied: high forest and coppice-with-standards. We studied separately effects related to the age of the tree at the time the ring was formed and effects attributable to environmental changes. At young ages, δ13C shows an increase of more than 1‰. However, age-related trends differ in high forest and coppice-with-standards. Changes in microenvironmental variables during stand maturation, and physiological changes related to structural development of the trees with ageing, could explain these results. During the past century, δ13C in tree rings shows a pattern of decline that is not paralleled by air δ13C changes. Isotopic discrimination has significantly decreased from 18·1 to 16·4‰ in high forest and varied insignificantly between 17·4 and 16·9‰ in coppice-with-standards. As a consequence, intrinsic water-use efficiency has increased by 44% in high forest and 23% in coppice-with-standards during the past century. These results accord with the increased water-use efficiency observed in controlled experiments under a CO2-enriched atmosphere. However, other environmental changes, such as nitrogen deposition, may be responsible for such trends.

Notes: We investigated (1) the effect of constant and altered inorganic phosphate (Pi) supply (1–100 mmol m–3) on proteoid root production by white lupin (Lupinus albus L.); and (2) the variation in citrate efflux, enzyme activity and phosphate uptake along the proteoid root axis in solution culture. Proteoid root formation was greatest at Pi solution concentrations of 1–10 mmol m–3 and was suppressed at 25 mmol m–3 Pi and higher. Except at 1 mmol m–3 Pi, the formation of proteoid roots did not affect plant dry matter yields or shoot to root dry matter ratios, indicating that proteoid roots can form under conditions of adequate P supply and not at the expense of dry matter production. Plants with over 50% of the root system as proteoid roots had tissue P concentrations considered adequate for maximum growth, providing additional evidence that proteoid roots can form on P-sufficient plants. There was an inverse relationship between the Pi concentration in the youngest mature leaf and proteoid root formation. Citrate efflux and the activities of enzymes associated with citric acid synthesis (phosphoenolpyruvate carboxylase and malate dehydrogenase) varied along the proteoid root axis, being greatest in young proteoid rootlets of the 1–3 cm region from the root tip. Citrate release from the 0–1 and 5–9 cm regions of the proteoid root was only 7% (per unit root length) of that from the 1–3 cm segment. Electrical potential and 32Pi uptake measurements showed that Pi uptake was more uniform along the proteoid root than citrate efflux.

Notes: The boring activity of microendolithic organisms such as cyanobacteria, chlorophytes, rhodophytes and fungi, represents a major destructive process affecting sediment preservation within reef environments. This study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north Jamaica, correlating to the upper (〈18 m depth) and lower (〉18 m depth) photic zones. The upper photic zone assemblage is dominated by cyanobacteria and chlorophytes, whilst rhodophytes and fungi become more abundant with increasing water depth. Most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types. The highest degree of grain infestation occurs within shallow, low-energy back-reef environments and the most susceptible grains (at all sites) are corals, molluscs and foraminifera. Coralline algae, Halimeda and echinoid fragments are rarely heavily infested. High rates of infestation at back-reef sites result in rapid diminution of the most susceptible grains, especially coral, which are either underrepresented, or contribute only to the finer sediment fractions, in the subsurface. Fore-reef grain assemblages undergo relatively little alteration. Microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains. The impact of microboring upon back-reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments.

Notes: Hueneme and Dume submarine fans in Santa Monica Basin consist of sandy channel and muddy levee facies on the upper fan, lenticular sand sheets on the middle fan, and thinly bedded turbidite and hemipelagic facies elsewhere. Fifteen widely correlatable key seismic reflections in high-resolution airgun and deep-towed boomer profiles subdivide the fan and basin deposits into time-slices that show different thickness and seismic-facies distributions, inferred to result from changes in Quaternary sea level and sediment supply. At times of low sea level, highly efficient turbidity currents generated by hyperpycnal flows or sediment failures at river deltas carry sand well out onto the middle-fan area. Thick, muddy flows formed rapidly prograding high levees mainly on the western (right-hand) side of three valleys that fed Hueneme fan at different times; the most recently active of the lowstand fan valleys, Hueneme fan valley, now heads in Hueneme Canyon. At times of high sea level, fans receive sand from submarine canyons that intercept littoral-drift cells and mixed sediment from earthquake-triggered slumps. Turbidity currents are confined to ‘underfit’ talweg channels in fan valleys and to steep, small, basin-margin fans like Dume fan. Mud is effectively separated from sand at high sea level and moves basinward across the shelf in plumes and in storm-generated lutite flows, contributing to a basin-floor blanket that is locally thicker than contemporary fan deposits and that onlaps older fans at the basin margin. The infilling of Santa Monica Basin has involved both fan and basin-floor aggradation accompanied by landward and basinward facies shifts. Progradation was restricted to the downslope growth of high muddy levees and the periodic basinward advance of the toe of the steeper and sandier Dume fan. Although the region is tectonically active, major sedimentation changes can be related to eustatic sea-level changes. The primary controls on facies shifts and fan growth appear to be an interplay of texture of source sediment, the efficiency with which turbidity currents transport sand, and the effects of delta distributary switching, all of which reflect sea-level changes.

Notes: Analysis of a large data base of ground-penetrating-radar (GPR) profiles from both natural and developed paraglacial barriers along the coast of New England has allowed identification of eight reflection configurations that characterize this type of mid- to high-latitude coastal environment. Bedrock anchor points yield primarily hyperbolic configurations, whereas glacial anchor points and sediment-source areas are characterized by chaotic, parallel, and tangential-oblique configurations. Beaches and dunes produce predominantly sigmoidal oblique, hummocky, reflection-free, and bounding-surface configurations. Back-barrier sediments may yield basin-fill configurations, but generally include abundant signal-attenuating units.The GPR data, calibrated with information from cores, were collected across swash-aligned and drift-aligned barriers in a variety of wave- and tidal-energy settings. Application of a 120-MHz antenna, as used in this study, enables portrayal of a range of sedimentary units, from individual bedforms (on single records) to entire barrier elements (using large numbers of intersecting GPR sections), at maximum vertical resolutions that vary between 0·2 m and 0·7 m.The most important drawback of GPR in the coastal environment is attenuation of the electromagnetic (EM) signal by layers of salt-marsh peat or by brackish or salty groundwater, primarily along barrier edges. This disadvantage is offset by many benefits. Data can be collected at rates of several km per day, making GPR an excellent reconnaissance tool. A core that is used in the calibration of GPR data can be matched with great accuracy to its position on the complementary GPR record, allowing detailed correlation between lithostratigraphy and reflection configuration.

Notes: The Pliocene Loreto basin is an asymmetrical half graben located on the eastern margin of Baja California Sur, Mexico, which formed by rapid subsidence along the dextral-normal Loreto fault. The southern Loreto basin contains numerous, well exposed coarse-grained Gilbert-type fan deltas that were derived from the footwall of the Loreto fault. Detailed sedimentological study of individual foreset beds provides information about down-slope flow transformations of cohesionless sediment gravity flows in shallow water. Deposits of Gilbert-delta foresets consist of ungraded, normal-graded, inverse- to normal-graded, and bipartite conglomerate and sandstone. Lateral transitions in sorting, grading style and internal structure are commonly observed within individual beds, both across and down slope, suggesting heterogeneity within flows and a close relationship between high-density turbidity currents and gravel traction carpets. A conceptual model for flow transformation and deposition of high-density turbidity currents on Gilbert-delta foreset slopes is developed for Pliocene strata in the Loreto basin. In this model, ungraded cohesionless debris flows evolved rapidly down-slope into normal-graded gravelly turbidity currents. With continued down-slope transport, the gravel fraction collapses and becomes concentrated into a basal traction carpet undergoing laminar shear, and is over-ridden by a sandy turbulent suspension. The short distances (10–20 m) over which lateral transitions within single beds are observed indicate very rapid flow transformations (10–20 s) and rapid deposition of gravel traction carpets by frictional freezing on and near the base of the foreset slope.

Notes: 1. Aquatic insects were quantitatively surveyed at five sites along the tidally influenced section of a river-dominated estuary in North Wales. Site 1 was the furthest upstream and was established as a reference site as it was never inundated by salt water. Site 5 was the furthest downstream and was inundated by all incoming tides. Numerically, insects made up 32% of the estuarine invertebrate fauna.2. Although the densities of most insect taxa decreased towards the estuary mouth, there were significant numbers present downstream for much of the year; for example, in April at site 4 (which was inundated by 81% of all high tides), a mean of 3514 chironomid larvae were recorded per m2 of estuary bed. Even at site 5, which was inundated twice daily, there were 747 larvae per m2. Among the larger aquatic insects, caddisfly and elmid beetle larvae, together with stonefly nymphs, were consistently taken at site 4 (e.g. maxima of forty-eight caddisfly larvae m–2 in December and seventy elmids m–2 in April), although their densities were lower than upstream.3. There were seasonal shifts in the longitudinal distribution of several taxa, most notably the extension of chironomids down the estuary in April and July, and the concentration of simuliid larvae and mayfly nymphs at site 2 in July. The total freshwater benthos showed a downstream shift between September and December, which was maintained through April and into the summer. The latter was despite peak saltwater inundation (highest tides) in October, November and April. In June and July, when saltwater intrusion was lowest, the ranges of many aquatic insects had contracted to sites 1 and 2.4. Laboratory experiments showed that virtually all individuals of nineteen species of insects collected from site 1 (freshwater) survived a 4-h immersion in 8.75‰ saltwater (25% strength seawater). Immersion in progressively more saline solutions reduced the survivorship of first the mayflies, followed by the caddisflies Glossosoma conformis and Hydropsyche instabilis. After 4 h in full strength seawater, all specimens of the stonefly Dinocras cephalotes, over half of the Perla bipunctata, and some individuals of nine species of caddisfly were alive. Four species of caddisfly (Sericostoma personatum, Odontocerum albicorne, Potamophylax cingulatus and Adicella reducta) survived a 24-h simulated tidal cycle of immersion. With the exception of P. cingulatus, a few individuals of these caddisfly species survived immersion in full-strength seawater for 24 h. For some individual species there was good agreement between their observed longitudinal distribution in the estuary and laboratory-measured salinity tolerance; however, there was no significant correlation, overall, for the fauna.

Notes: 1. This study presents a qualitative and quantitative survey of epibionts infesting two populations of the freshwater isopod Asellus aquaticus (L.). Using scanning electron microscopy, the prevalence, mean intensity, abundance, spatial preferences and distribution of organisms on various external surfaces were ascertained.2. A diverse community, consisting primarily of protozoa and rotifers, utilised A. aquaticus as a substrate organism. Every individual A. aquaticus supported some form of epizoic life. Peritrich species comprised 89.2% of all epibionts. Carchesium polypinum, Pseudocarchesium aselli, Pseudocarchesium asellicola, Pseudocarchesium simulans and Opercularia hebes dominated the epifauna.3. Highest epibiont burdens occurred on the mouthparts, the first few ventral segments and the gills and largely comprised the above peritrich species. Most epibionts exhibited some degree of site preference on the host. A distinct gill epifauna existed. Apart from Acineta tuberosa and Vorticella rotunda, which had equal prevalences on dorsal and ventral surfaces in one culture, most species largely avoided the dorsal surface.4. Epibionts exhibited varying degrees of adaptation to life on a living substrate. They ranged from facultative species such as A. tuberosa, which are capable of colonising abiotic substrata, to Gymnodinoides aselli whose life cycle relies on interaction with A. aquaticus. Highly specialised species tended to exhibit the most pronounced and consistent site restriction.5. Asellus aquaticus offers a highly tractable system for further study of substrate species–epibiont relationships.

Notes: 1. The assemblage of suspension-feeding microcrustaceans in lakes changes along a habitat gradient from nearshore to offshore. This gradient of microcrustaceans was explored in relation to differences in macrophytes and the associated changes in water chemistry, food resources and types of predators.2. Some microcrustacean species were littoral or limnetic specialists, while others changed their distribution along this horizontal habitat gradient on a diel or seasonal basis. Distribution patterns were similar in a lake and a pond which differed in extent of macrophyte habitat.3. There was a large shift in the composition of sestonic food, indicating heterotrophic seston nearshore and more autotrophic seston offshore. Sit-and-wait predators of microcrustaceans (e.g. Enallagma spp.) dominated nearshore and cruising predators (e.g. Leptodora kindtii Focke) were more common offshore.4. A reciprocal transplant experiment revealed that littoral specialists could survive equally well when fed littoral or limnetic seston, while limnetic specialists performed poorly when fed littoral seston. Food resources may be important in determining where some microcrustacean species live along this horizontal habitat gradient.

Notes: 1. In ecological studies on freshwater crayfish, determination of basic population parameters is often complicated by the lack of a suitable age estimation method.2. Previously, lipofuscin age pigment in the olfactory lobe cell masses (OLCM) of short-lived tropical crayfish has been used for accurate age determination. Here we present the first test of this method on a longer-lived, temperate species, the signal crayfish, Pacifastacus leniusculus.3. Confocal fluorescence microscopy and image analysis of histological sections were used to quantify OLCM lipofuscin in a reference sample of Swedish P. leniusculus from several known year-classes, reared under naturally variable temperature conditions. Lipofuscin concentration was linearly associated with age (r2 = 92.4%) and produced much more accurate age estimates than conventional body size-based procedures.4. A model derived from the crayfish of known-age was used to estimate the ages of wild P. leniusculus from an English stream. The relationship between lipofuscin-estimated age and carapace length suggested relatively slow growth in this wild population, consistent with a high population density and severe competition. The analysis also extended the known longevity of P. leniusculus to approximately 16 years.5. The lipofuscin method for determining age and growth may be widely applicable to freshwater crayfish, with probable further potential both within and outside the Crustacea.

Notes: 1. The nutritional value of detrital aggregate, which refers to the mixture of plant debris (i.e. organic detritus) and microorganisms, in the diets of fathead minnows (Pimephales promelas Rafinesque) was assessed in experiments using surface benthic samples from three sites in Clear Lake (Houghton County, Michigan, U.S.A.).2. In the first experiment, fish were fed small (〈250 μm) and large (250–1000 μm) particle detritus from one profundal and two littoral sites. Fish in all treatments lost weight. However, fish fed detritus from the littoral erosional site, where wild fish forage intensively, had significantly lower weight loss.3. In the second experiment, fish were fed various quantities of Artemia with or without ad libitum erosional site detritus. Growth was proportional to the mass of Artemia consumed, yet minnows showed increased growth with the detritus supplement at low invertebrate rations.4. This study shows that detrital aggregate produced by decompositional processes at the erosional site could be nutritionally valuable to minnows. It appears that a feeding strategy of consuming detritus with a higher nutritional quality (i.e. detrital aggregate) as a dietary supplement benefits fishes in temperate as well as tropical systems.

Notes: 1. A survey was made of denitrification and nitrous oxide (N2O) production in river sediments at fifty sites in north-east England during one season in order to investigate the relationship between rates and environmental factors likely to influence these processes. The sites were chosen to represent a wide range of physical and chemical conditions. Denitrification rate and N2O production were measured within 5 h of sampling using the slurry acetylene blockage technique.2. Denitrification rate ranged from less than 0.005–260 nmol N g–1 DW h–1, tending to increase in a downstream direction. N2O production ranged from negative values (net consumption) to 13 nmol N2O-N g–1 DW h–1 and accounted for 0–115% of the N gases produced.3. Denitrification rate and N2O concentration in the sediment were correlated positively with nitrate concentration in the water column, water content of the sediment and percentage of fine (〈 100 μm) particles in the sediment.4. The variation in denitrification rate was satisfactorily explained (64% total variance) by a model employing measurements of water nitrate and water content of sediments. No simple or multiple relationship was found for N2O production.

Notes: 1. A novel method was used to determine if the statutory regulation of drift-netting at the mouth of the River Usk in Wales was associated with a significant improvement in the stock and rod catch of salmon in the river upstream.2. A linear regression model was constructed, in which the annual rod catch of salmon declared from the Usk between 1977 and 1988 was the dependent variable and the simultaneous annual catch declared from the nearby River Wye was the independent variable. The model was extrapolated to project the annual rod catches of salmon on the Usk, relative to the Wye, between 1989 and 1995.3. The model accurately projected the actual rod catches declared from the Usk in 1989, 1990 and 1991. However, between 1992 and 1995 the declared catches deviated significantly (P≤ 0.05) from those projected by the model. The upsurge in rod catches declared after 1992 from the Usk, relative to the Wye was concomitant with the regulation of estuarine drift-netting.4. It was concluded that diminished estuarine exploitation had a beneficial impact on salmon angling success on the Usk. However, the utility of the model was restricted by inconsistencies in the methods used to generate the data, by changes in fishery management policies and by a lack of essential information on the interrelationships between catch, effort, stock and environmental conditions.

Notes: 1. The algae and sedentary macroinvertebrates on the upper surface of stones from the littoral of Crosemere were investigated over 13 months. This lake is one of a series of eutrophic meres of glacial origin in the English Midlands.2. Stones were taken from shallow and deep areas in the littoral and from areas shaded by bankside trees and those away from trees. This gave four habitat types: open/shallow; open/deep; shade/shallow; shade/deep. Epilithic algae and sedentary macroinvertebrates from the upper surfaces of the stones were quantified monthly for each habitat type.3. Chlorophyll a and ash-free dry mass both showed a strong seasonal pattern common to all habitat types, with a spring peak declining to a summer minimum, followed by a small autumn recovery, and a winter minimum.4. In terms of percentage cover, Cladophora glomerata showed a markedly different pattern. There were strong differences between habitat types, with shaded stones from the shallows, in particular, having very sparse Cladophora cover. In the open, Cladophora cover was high in summer and low at other times.5. The invertebrate community was dominated by retreat-dwelling larvae of the psychomyiid caddis, Tinodes waeneri, and four species of chironomids with tube-building larvae, Cricotopus sylvestris, Microtendipes pedellus, Glyptotendipes pallens and Endochironomus albipennis. For Tinodes, Cricotopus and Microtendipes, peaks of density occurred chiefly beneath trees in spring and summer.6. The seasonal pattern of algal abundance showed little relationship with that of invertebrate biomass. The ratio of chlorophyll a to ash-free dry mass also declined in summer, despite the higher invertebrate biomass. This indicated that grazing was not the dominant factor diminishing algal abundance seasonally. It seems likely that algae were limited chiefly by physical factors, such as light and temperature, and by nutrients, particularly nitrates, which decline in summer in the epilimnion of the lake.7. Grazing may have contributed to spatial patchiness of algae in summer, however, particularly that of Cladophora. The scarcity of Cladophora on shallow, shaded stones coincided with a high abundance of Tinodes on these stones in early summer. Riparian trees could thus have affected epilithic algae, not only by shading but also indirectly through the supply of grazers.

Notes: 1. By the aid of a computer technique, the in situ variations in heart rate and locomotor activity were recorded continuously for 7 days in sixteen individuals of the crayfish, Astacus astacus (Linnaeus 1758), in association with natural changes in water temperature and light intensity.2. All sixteen crayfish investigated were found to express circadian rhythmicity in heart rate with a periodicity of ≈ 24 h. For 88% of the animals investigated, rhythmicity was significant (P 〈 0.05). Ninety-three per cent of the crayfish showed circadian rhythmicity in locomotor activity with a 24 ± 2 h periodicity and, for 67% of the animals, this rhythmicity was significant (P 〈 0.05). In general, the expression of circadian rhythms was associated with nocturnal behaviour, heart rates and locomotor activity levels being higher at night than by day.3. A positive correlation was observed between heart rate and locomotor activity. Temperature and light intensity exerted positive and negative influences on heart rate in A. astacus, respectively.4. In the first experiment, 84% of the variation in heart rate could be explained by the changes in locomotor activity, temperature and light intensity. In the second experiment 35% of the variation in the heart rate was explained using these parameters.

Notes: 1. The rate of grazing damage experienced by submersed and floating leaves of water lilies (Nuphar variegata and Nymphaea odorata) was monitored in lakes in the Upper Peninsula of Michigan, U.S.A. Herbivores damaged 0.2–1.7% of the leaf surface of water lilies per day. These grazing rates differed between plant species, between submersed and floating leaves, and between lakes. Some leaves had more than 60% of their surface damaged and an overall mean of 16% damage occurred during the 2–3 week monitoring period of this study.2. Snapshot measurements of grazing damage on randomly collected submersed and floating leaves of Nuphar showed that submersed leaves were more damaged (11.0 ± 1.6%, n = 84) than floating leaves (3.8 ± 0.6%, n = 92). Overall, these 176 Nuphar leaves had 7.2% of their area damaged.3. Five species of herbivorous insects were commonly found on water lilies (Nymphaeacea). One primarily aquatic insect (sensuNewman 1991), a caddisfly larva (Trichoptera: Limniphilidae), had a generalized diet of water lilies, other macrophytes, algae, and detritus. Four of the five insects were from primarily terrestrial insect groups (Coleoptera and Diptera;‘secondary invaders’, sensuNewman 1991) and consumed only water lilies in food preference experiments.4. The feeding preferences of the generalist trichopteran were altered when the macrophytes were freeze-dried, ground into a powder, and reconstituted in an alginate gel. This suggests that plant structure may be an important feeding determinant for this insect. In contrast, a specialist weevil preferred its host plant in choice assays, regardless of whether fresh tissue or reconstituted macrophytes were used, suggesting this insect cued on a unique, non-structural property of its host plant.5. These results suggest that herbivory on freshwater macrophytes is of a similar magnitude to that on terrestrial plants. The findings of this study are consistent with the hypothesis that herbivorous insects of primarily terrestrial groups have a narrower diet breadth than insects of primarily aquatic groups.

Notes: 1. Phosphorus (P) uptake by macrophytes and epiphytes from the LaPlatte River (VT) was examined in the laboratory by adding 32PO4-P to recirculating stream microcosms.2. Water, plugs of sediment and plants were removed from the river and placed into the microcosms. 32PO4-P was then added either to the water or the sediment, and its incorporation into plants and epiphytes was monitored over 3 days. Uptake was examined at both ambient (5 μg L–1) and increased (50 μg L–1) soluble reactive phosphorus (SRP) concentrations. A computer program was developed to fit curves to the radiotracer data and calculate rate constants for the simultaneous transfer of 32P among compartments.3. Both macrophytes and epiphytes removed P from the water, but epiphyte uptake of P was more rapid. Phosphate enrichment stimulated P uptake by both macrophytes and epiphytes. Macrophytes also obtained P from the sediment. The relative contribution of P to macrophytes from the water vs. that from the sediment appeared to vary with SRP in the overlying water. Accurate estimates of rates of P uptake from sediments by macrophytes were difficult to obtain however, due to very low and highly variable unit rate constants for P uptake and uncertainty about the magnitude of the phosphate pool available for uptake.4. SRP concentrations were greater in the overlying water than in the sediment pore water of stream microcosms in the present study. Numerous reports in the literature have suggested that this condition favours uptake by macrophyte stems and leaves rather than by roots.5. Phosphate uptake from the water by macrophytes in shallow streams may be more common than for macrophytes in lakes.

Notes: 1. The feeding methods and intensity of predation by larvae of the damselfly Erythromma najas on leaf-mining larvae of the chironomid Glyptotendipes gripekoveni were examined in artificial habitats differing in complexity. The experiments assessed the influence of chemical stimuli from the predator, light and the concentration of suspended food on the feeding activity of G. gripekoveni inside and outside of the mine.2. Erythromma najas preyed upon G. gripekoveni as the latter grazed outside mines. The intensity of this predation decreased significantly at night in a habitat offering alternative prey.3. When the food concentration for the chironomid was high, it significantly reduced both filtering activity and activity outside mines in response to the kairomone produced by E. najas. Feeding activity did not change when food was scarce.4. The induced reduction in filter-feeding and deposit-feeding activity probably reduced predator success by reducing the probability of long-distance detection of a mine and location of the chironomid’s hole.5. The predator can detect and catch mining prey in either the light (visually) or dark (mechanically). This may explain the lack of diel periodicity in the chemically induced differences in prey activity.6. Reduced feeding activity of mining larvae in the chemically simulated presence of a larval damselfly can be explained as an induced antipredator behaviour, illustrating the trade-off between feeding demands and predation risk in a poorly known link of the littoral foodweb.

Notes: 1. To investigate direct effects of zebra mussel (Dreissena polymorpha) feeding activities on phytoplankton community composition, short-term microcosm experiments were performed in natural water with complex phytoplankton communities. Both gross effects (without resuspension of mussel excretions) and net effects (with resuspension) were studied.2. Gross clearance rates were not selective; essentially all taxa were removed at similar rates ranging from 24 to 63 mL mussel–1 h–1. Net clearance rates were highly selective; different plankton taxa were removed at very different rates, ranging from 12 to 83% of the gross rates, leading to consistent changes in the phytoplankton community composition. Thus, although zebra mussels can cause most phytoplankton to decline, there is considerable variation among taxa in either pre-digestive selection or post-digestive survival.3. The direct, short-term effects of zebra mussels on phytoplankton community composition are consistent with some of the major changes observed in the Hudson River since establishment of zebra mussels.4. We show, with simple calculations, how zebra mussel filtration rate, its selective efficiency on various taxa, and phytoplankton growth rates interact to produce changes in the phytoplankton composition.

Notes: 1. Cosmarium abbreviatum var. planctonicum, a desmid from oligo-mesotrophic lakes, had a higher maximum alkaline phosphatase activity (APA) and affinity constant under both continuous and pulsed inorganic phosphorus (Pi) limitation than Staurastrum chaetoceras, a desmid predominantly encountered in eutrophic lakes.2. APA of both species increased when measured in starved cells subjected to pulsed Pi conditions when compared to continuous Pi limitation.3. The portion of extracellular relative to cellular APA was higher in S. chaetoceras than in C. abbreviatum, indicating that S. chaetoceras secreted the enzymes more readily into its environment.4. The difference in APA could explain the dominance of C. abbreviatum during competition between these two species under conditions of continuous organic P (Po) limitation, but not the outcome under a pulsed Po shortage. The dominance of S. chaetoceras in the latter experiment can, however, be explained by species-specific Pi-uptake characteristics.5. After a saturating pulse of Pi, no increase in Pi in the extracellular mucus layer of C. abbreviatum was found and it was therefore concluded that the mucilage sheath does not store P. However, the sheath could have a main function as an accumulation site of cellular APA, providing the cell with Pi.

Notes: 1. The macroinvertebrate fauna living on stones in the exposed stony littorals of thirty-nine Danish lakes were examined by multivariate numerical methods. The data were derived from 125 semi-quantitative samples and a species list of 126 taxa. The mean number of individuals per sample was 960, and among the most common taxa were Asellus aquaticus, Gammarus, Oulimnius, Tinodes, Cricotopus and Dicrotendipes.2. The total number of species and fourteen individual taxa were positively correlated to mean depth of the lakes and eleven taxa were correlated to the total phosphorus concentration. The Shannon diversity was negatively correlated to the chlorophyll a concentration ([Chl a]).3. Community patterns were examined by detrended correspondence analysis (DCA), and the relationship between species data and selected environmental variables was analysed by canonical correspondence analysis (CCA). Mean lake depth was found to be the strongest environmental variable in explaining the species data. The [Chl a] and Secchi depth also explained significant variation in the distribution of the stony littoral invertebrates. Wind fetch and relative exposure did not explain any variation in the faunal composition among sites.4. The abilities of the macroinvertebrates to predict the lake trophic state, expressed as log ([Chl a]), were explored by means of weighted averaging (WA) regression and calibration. Two tolerance-weighted WA models using inverse and classical regression for deshrinking are presented. The models were assessed by the root mean square error (RMSE) of prediction, using bootstrapping as cross validation, and by the correlation between observed and inferred log ([Chl a]). The model using inverse deshrinking had a RMSEboot = 0.41 and r2 = 0.63. By using classical regression, the predictability in the ends of the gradient was improved but the RMSE increased: RMSEboot = 0.46.5. Although the factors determining faunal distribution patterns in the Danish lowland lakes were highly multivariate and difficult to disentangle, it seems reasonable to use the WA estimated species optima and tolerances to [Chl a] in a bio-assessment model.

Notes: 1. The hypothesis that body storage is used by daphniids as a physiological cue for adaptively adjusting egg size and number to food availability was tested.2. Egg size and number were examined to see whether they are related to individual variation in body storage independent of maternal size, genotype and food level. Egg mass and brood size (number of eggs in a brood) were compared to somatic mass, all adjusted to maternal body length, at two food levels in two parthenogenetic clones of Daphnia magna.3. The prediction that adjusted brood size should increase with body storage, whereas adjusted egg mass should decrease with increasing body storage, was not fulfilled as seven of eight comparisons failed to fit the expectation.4. It is concluded that body storage is probably not the food-availability cue used by daphniids to control intrabrood resource allocation. Other possibilities, such as chemical cues emitted by food organisms and by coexisting cladocerans, are briefly discussed.

Notes: 1. The total phosphorus–algal biomass relationship from a set of turbid tropical ponds in Kenya was compared with predictions derived from surveys of temperate and subtropical lakes. Despite high concentrations of total phosphorus (TP) (up to 797 μg L–1) and inorganic turbidity (up to 800 mg L–1), the log–log relationship between algal biomass and TP was steeper than expected.2. No evidence of nitrogen limitation was found at high TP, and total nitrogen (TN):TP ratios were higher than in lakes with similar TP levels studied previously. High TN:TP ratios may be a consequence of excretion by cattle into the ponds, a nutrient source characterized by a high ratio of available N to available P.3. Despite extremely high turbidity, the ratio of mixed layer depth to euphotic depth was generally low because these ponds are shallow (≤ 2 m), and was not related to algal yield. A positive relationship was also found between TP and zooplankton biomass, and between TP and the density of the zooplanktivorous bug, Anisops. In contrast, no relationship was found between fish biomass and TP, algal biomass or zooplankton biomass.

Notes: 1. Hydrological exchange between the surface stream and the hyporheic zone is well documented in the main channel of rivers, especially at the reach scale. Hydrological processes of advection/convection occur at different scales, and in secondary channels of large rivers little is known about these exchanges in the hyporheic zone on a broad scale (i.e. kilometres). This work studied exchanges of water and biota in a secondary channel on a large scale (4 km), using a three-dimensional framework.2. The exchanges of water were described using physicochemical indicators of surface and groundwaters. Samples of water and biota were taken in three dimensions: (i) vertically from benthic (i.e. 0.20 m below the surface of the substratum) to hyporheic (0.50 m) and deep interstitial (1.0 m) zones; (ii) laterally from the right to the left bank (i.e. right, middle and left positions); and (iii) longitudinally from upstream to downstream (seven stations regularly distributed along the channel).3. The physicochemical indicators clearly revealed hydrological heterogeneity in the longitudinal and vertical dimensions, whereas lateral variability was not significant.4. Spatial distribution of biota exhibited strong longitudinal variations that were not gradual as predicted by an upstream/downstream continuum, but patchy and discontinuous. No significant differences were found between the three positions across the channel.5. Analyses of both physicochemical and faunal data sets produced matched ordination of samples and stations, indicating that interstitial–surface flow relationships appear to be an important governing factor in the distribution of interstitial biota at this broad scale.6. Results are discussed in relation to the hypothetical three-dimensional models of the hyporheic zone in rivers. Contrasting with other observations on the main channel (where advection/convection patterns are dominated by morphological changes of the river-bed morphology), it is proposed that water exchanges in backwaters are more likely to be related to local modifications of stream-bed porosity.

Notes: 1. Diadromy is a dominating behavioural characteristic of fish faunas in New Zealand rivers, with amphidromy and catadromy being the most common strategies.2. Juvenile life stages of amphidromous and catadromous species migrate from the sea, through river systems, to find habitats for feeding, growth, maturation and reproduction.3. Studies of fish distributions in rivers of the West Coast of the South Island of New Zealand show that, in most species, these migrations result in more or less continuous distributions from the lower reaches to the upstream limits of each species’ range.4. Upstream penetration of rivers varies widely between species and this generates downstream–upstream trajectories of declining species richness.5. Parallel trajectories of declining downstream–upstream abundance are likely in each species.6. These patterns demonstrate the presence of downstream–upstream linkages in the community ecology of freshwater fishes in New Zealand rivers.

Notes: 1. Oligotrophic ‘Lobelia-lakes’ are rare in Denmark. The few that have survived widespread eutrophication are in uncultivated sandy regions and are threatened by acidification and increased nutrient deposition from the atmosphere. Grane Langsø was considered the clearest lake in Denmark in the 1950s, when isoetids grew to 5.5 m depth and characeans covered the deepest part of the lake bottom at 11.5 m. The goal of the study reported here was to examine whether the lake has maintained this high quality by studying the development of macrophyte distribution and composition in relation to the changes in pH, nutrient conditions and transparency over the past 40 years.2. Aquatic mosses now dominate the vegetation rather than rooted isoetids, probably as a result of acidification (summer median pH was 5.60 in 1958–1963 compared to 5.07 in 1976–1994). Along with a reduced median pH, annual pH fluctuations have increased from about 0.3 units 40 years ago to 0.9 units today.3. The depth limit of isoetid species has declined markedly and Nitella flexilis, which previously dominated the dense bottom vegetation in the hypolimnion, has disappeared. These changes can be accounted for by reduced light penetration and an increased cover of filamentous green algae and mosses on the isoetid species.4. The decline in light penetration was mainly caused by increased humic content following storm falls in 1981–84, but increased nutrient deposition may also have stimulated the growth of phytoplankton and filamentous green algae. The restricted macrophyte growth in the hypolimnion during summer can account for the change from oxygen supersaturation 40 years ago to anoxia today. The reduced light penetration has resulted in cooling of the hypolimnion, thereby increasing the stability and duration of thermal stratification. This increases the likelihood of anoxia in August–September. Profound changes in the plant community and in oxygen conditions have occurred, even though the decline of pH has been small and long-term changes in nutrient concentration have been difficult to detect.

Notes: 1. In this field study, diatom-specific and bacteria-specific fatty acids were used as biomarkers to evaluate the differences in diet between Chironomus plumosus (a spring-emerging cohort) and C. anthracinus (an autumn-emerging cohort), and Procladius spp. Furthermore, total lipid content of Chironomus larvae was analysed.2. Individual dry mass of the spring cohort of C. plumosus rapidly increased during spring and early summer. Surprisingly, the autumn-emerging cohort showed remarkably little growth over the same time interval. The individual dry mass of C. anthracinus initially declined in early spring, but then increased during April and May.3. Accumulation of the diatom-specific fatty acid palmitoleic acid (16 : 1ω7) during spring was much higher in C. plumosus (〉 3-fold increase) than in C. anthracinus (1.5-fold). Conversely, the bacterial indicating iso form of septadecanoic acid (17 : 0i) was higher in C. anthracinus than in the spring-emerging cohort of C. plumosus. This shows that C. plumosus assimilates energy from the spring diatom bloom to a greater degree, whereas C. anthracinus feeds more exclusively on detritus in the sediment.4. Concentrations of 17 : 0i in Procladius larvae were 0.54 ± 0.13 mg g–1, i.e. consistently higher than for both Chironomus taxa, indicating that this predator gains a relatively high fraction of its energy through detrital pathways (from bacteria).5. These results show that fatty acid biomarkers can be an appropriate tool to detect differences in larval diet between coexisting chironomid species, between two closely related Chironomus species and between different cohorts.6. The different feeding modes of both Chironomus species may be important for among-lake distribution patterns, with filter-feeding C. plumosus being dominant in relatively shallow lakes and deposit-feeding C. anthracinus more common in deeper lakes with stable stratifications. This conjecture was supported by a compilation of data from Lake Mälaren.

Notes: 1. The effects of woody debris on stream habitat of juvenile masu salmon (Oncorhynchus masou) were examined at two spatial scales, stream reach and channel unit, for first- to third-order tributaries of the Teshio River in northern Hokkaido, Japan. The forty-eight study reaches were classified into three distinct types: coarse-substrate step-pool (CSP), coarse-substrate pool–riffle (CPR) and fine-substrate pool–riffle (FPR) reaches. Each reach type included reaches with different riparian settings, broadly classified as forest (relatively undisturbed forest and secondary forest after fires) or grassland (bamboo bushland and pasture).2. The reach-scale analyses showed that neither total pool volume nor pool-to-pool spacing was correlated with woody debris abundance in any of the three reach types. Masu salmon density was positively correlated with both woody-debris cover area and total cover area, but not with total pool volume in the reaches.3. Channel-unit-scale analyses revealed that woody debris reduced non-pool velocity, increased pool depth and retained fine sediment in pools in FPR reaches, where the size of woody debris was very large relative to the substrate material size. However, woody debris did not influence any of the hydraulic variables (depth, velocity, substrate) in either non-pools or pools of CSP and CPR reaches. Habitat use by masu salmon in non-pools or pools was affected by woody-debris cover area or total cover area rather than by hydraulic variables in any of the reach types.4. The effects of woody debris on habitat at the reach- and channel-unit scales in the study area were less than those indicated by previous work in the Pacific Northwest, North America, owing to the relatively small size of the riparian trees. However, the overall results suggested that woody debris in the study area contributed to masu salmon habitat by providing cover at the smaller, microhabitat scale.

Notes: 1. A new marking technique was developed and used to track individual water flea behaviour. A single clone of Ceriodaphnia reticulata exhibited no significant differences in mean depth, mean activity (antennae beats used in swimming), and mean travel (total vertical displacement) for fast-green dyed and control animals (n = 30, each treatment).2. Individual and group antipredator responses were recorded in three vertebrate predator densities (three odour concentrations of green sunfish Lepomis cyanellus; 0.00, 0.03 and 0.10 fish L–1) and four water flea group sizes (1, 5, 15 and 25), with n = 18 for each of the twelve treatment combinations. Water flea groups were probably mixtures of clones. Differences in behaviour after addition of predator odour showed that increasing predator density increased mean depth of marked individuals and mean proportion of water fleas descending. Additionally, increasing prey density decreased both mean depth of marked individuals and mean proportion of water fleas descending.3. Predator density and prey density had opposing affects on activity and travel for marked individuals. Higher predator density decreased mean activity (antennae beats), yet increased mean travel. Higher prey density increased mean activity, but decreased mean travel. Descending animals altered their swimming pattern by using fewer swimming beats to travel greater vertical distances in the presence of predator odour.

Notes: 1. An experimental field study examined the aggregation of stream macroinvertebrates associated with leaf packs over different spatial scales (several metres–km) (extent), at different patch sizes (grain) and temporal scales (2 and 4 weeks).2. Standardized leaf packs were constructed and set in eighteen blocks of nine equally spaced packs in glide areas over a 2 km stretch of a wooded stream. The distribution of macroinvertebrates colonizing the artificial leaf packs was investigated to examine the extent of both intraspecific and interspecific aggregation across leaf packs.3. All major colonizing taxa were intraspecifically aggregated across the leaf packs. Aggregation decreased with increasing patch size (grain) (from pack to block), and also decreased with decreasing spatial extent (from 2 km stretch to within-block scale) with patch size held constant. Interspecific associations among all major taxa were not common on most occasions at the short temporal scale, although the proportion of significant associations tended to increase somewhat over time and with spatial scale, but did not exceed 42% of all possible associations. The vast majority of significant associations were positive rather than negative.4. The influence of heterogeneity in a number of environmental variables measured for each leaf pack (accumulated detritus and sediment, leaf mass, flow and depth) on the distribution of invertebrates was considered, but this could only partially explain the variation in macroinvertebrate abundance across leaf packs.5. The roles of intrinsic aggregation and stochastic processes were examined as alternative explanations for the distribution patterns observed. It is apparent from this study that intrinsic aggregation, in concert with resource partitioning, influences the community structure of stream macroinvertebrates associated with leaf packs. These findings may also have implications for the distribution of taxa in the benthos as a whole.

Notes: 1. The role of sediment phosphorus (P) and nitrogen (N) in regulating growth of rooted macrophytes in a Canadian prairie river was investigated by means of in situ observations and artificial stream fertilization experiments.2. Biomass and percentage cover of rooted macrophytes in the South Saskatchewan River increased downstream of a municipal sewage treatment plant, with maximum abundance occurring between 25 and 100 km downstream of the outfall. Biomass in the river was related to sediment P but not N concentration, although sites of maximum biomass did not coincide with sites of maximum sediment P concentration.3. Artificial stream experiments revealed that while biomass was unaffected by addition of N to the sediment, it was enhanced by the addition of P to sediments, and further enhanced with the addition of N and P together, indicating a primarily P-limited system, with secondary N limitation when P is in excess.4. Macrophyte biomass increased linearly with increasing sediment P concentration in the artificial streams, and tissue P concentration peaked at ≈ 400 μg g–1. Biomass did not respond to increasing sediment N concentration, and only a weak relationship was observed between tissue N and sediment N, with maximum tissue N corresponding to ≈ 140 μg g–1 sediment exchangeable N.5. A lack of concurrence between the sediment P concentration producing maximum biomass and tissue P concentration in situ vs. under experimental conditions indicates that other environmental factors have an important role in regulating macrophyte growth in rivers. Thus, while nutrient control may be one element in a river macrophyte control programme, a holistic ecosystem approach should be adopted to account for the other factors that may affect the growth of rooted plants.

Notes: 1. Few studies have assessed the effects of macroconsumers, such as fishes and shrimps, on detritus and detritivores.2. We used an underwater electric field to prevent macroconsumers from feeding in and on leaf packs in a lowland stream in Costa Rica and thus to determine their effects on the density of insect detritivores and decay rates of leaves.3. Exclusion of macroconsumers resulted in significantly higher densities of small invertebrates inhabiting leaf packs. Most of these were collector–gatherers, none were shredders.4. Despite the increase in invertebrate density, decay rates of leaves were not statistically different. These findings contrast with results from temperate streams showing that increases in the density of invertebrates in leaf packs typically result in an increased rate of decay.5. Leaf decay rates and invertebrate densities were also compared between leaf packs placed in electric exclusion treatments and those placed in coarse (2 cm) plastic net bags (as used in many previous studies). Our results suggest that using such netting in tropical streams may deter macroconsumers, which can affect insect density and, potentially, decay rates of organic matter.

Notes: 1. The rate of microbial respiration on fine-grained stream sediments was measured at 196 first- to third-order sites in the mid-Atlantic region of the United States.2. Sample collection took place between April and July in 1993, 1994 and 1995.3. Study streams were randomly selected from the United States Environmental Protection Agency’s (USEPA) River Reach File (RF3) using the sample design developed by USEPAs Environmental Monitoring and Assessment Programme (EMAP).4. Respiration rate ranged from 0 to 0.622 g O2 g–1 ash-free dry mass (AFDM) h–1, and was significantly correlated with stream temperature, water chemistry and physical habitat.5. Respiration rate was significantly higher in streams from the Chesapeake drainage area compared to those from the Ohio drainage area, and in streams from the Northern Appalachian Plateau and Uplands and Central Appalachian Valleys ecoregions compared with streams from the Blue Ridge and Central Appalachian Plateau ecoregions.6. Respiration was not significantly different among stream orders or between years.

Notes: 1. At two organically polluted sites in the River Nethravathi, banyan and eucalypt leaves were colonized by one or two species of aquatic hyphomycetes. A total of three or four species were identified at the two sites in samples of water and naturally occurring leaves.2. Spore production from stream-exposed leaves by aquatic hyphomycetes was lower by a factor of up to 1 million compared with an earlier study in geographically close but unpolluted streams.3. Exponential decay rates and loss rates of phosphorus and calcium, were not statistically different from an earlier study in unpolluted streams. Nitrogen increased during decomposition more slowly in the current study.4. The microbial community on both leaves released enzymes active against starch, pectin, cellulose and xylan.5. Banyan leaves conditioned for 12 weeks were more palatable to the gastropod Notopala sp. than unconditioned leaves.6. Together with earlier data from unpolluted streams, the study provides evidence that organic pollution severely restricts diversity of aquatic hyphomycetes and their reproductive output, but does not have an equally strong effect on ecological functions generally associated with this group.

Notes: 1. A sample of adult signal crayfish were taken from a pond with a hepatotoxic bloom of the benthic cyanobacterium Oscillatoria sancta. Cyanobacteria were found in the stomachs of thirty-one out of thirty-two crayfish examined.2. To examine the effect of hepatotoxic cyanobacteria on crayfish a 14-day feeding trial was carried out with thirty-six animals. There were three treatments: (i) hepatotoxic and (ii) non-toxic Planktothrix agardhii; and (iii) crayfish pellets as a control.3. High-performance liquid chromatography (HPLC) showed that microcystins (the toxins of P. agardhii) had accumulated in the hepatopancreas of 50% of the animals in the toxic treatment.4. The cyanobacteria did not appear to have any negative impact on the crayfish. All crayfish survived, remained motile and ate throughout the experiment.5. During the experiment blood samples were taken and the total number of haemocytes counted. At the end of the experiment glucose concentration and relative wet weight of the hepatopancreas were measured. No differences between crayfish fed on toxic and non-toxic P. agardhii and the controls were found.6. The fact that microcystin accumulates in the crayfish hepatopancreas indicates that the toxin may be transferred further up the food chain.

Notes: 1. A method for quantifying interstitial water velocity based on the dissolution rate of plaster of Paris standards was developed as part of a study of vertical, longitudinal (1–4 order sites) and seasonal variation in the biotic and physical characteristics of the shallow hyporheic zone (0–30 cm) of a headwater stream system in West Virginia, U.S.A.2. A calibration model was developed using a water velocity simulation tank to relate mass loss of plaster standards to water velocity and temperature. The model was then used to calculate water velocity through artificial substrata embedded in the shallow hyporheic zone of four stream reaches based on in situ mass loss of plaster standards.3. Water velocity in the hyporheic zone increased with stream order, was highest in early spring and winter during high stream base flows, and decreased with depth into the substratum. There was a strong interaction between depth and season: during periods of high stream discharge, water velocity through the upper level of the shallow hyporheic zone (0–10 cm into the substrate) increased disproportionately more than velocity at greater depths. Mean interstitial velocity in March ranged from 0 cm s–1 in the lowest level (20–30 cm) to 3.5 cm s–1 at the upper level (0–10 cm) at the first-order site, and from 2.5 cm s–1 (20–30 cm) to 9.5 cm s–1 (0–10 cm s–1) at the fourth-order site. Gradients in stream discharge and sediment permeability accounted for treatment effects.4. Use of calibrated data improved the ability to resolve among-season differences in interstitial water movement over the use of uncalibrated mass loss data. For some applications of the plaster standard method, empirical calibration may not be necessary.

Notes: 1. A model developed over 20 years ago has been used to estimate daily food intake in brown trout living in streams and lakes over a wide geographical range. The chief disadvantages of this early model are that it is not continuous and requires twelve parameters, not all of which can be interpreted biologically. A new model, using a larger data set, was therefore developed to overcome these problems and estimate the mean daily energy intake.2. The two data sets used to develop the original model were also used to develop the general form of the new one, but a third data set was used to specify the model more precisely and to estimate the parameters. This third data set originated from experiments in which 185 trout (live weight range 1–350 g) were kept individually at 19 constant temperatures (range 3.8–21.7 °C) usually for 5–6 weeks. They were fed freshly killed shrimps (Gammarus pulex) and their food consumption was recorded throughout each experiment.3. Five, six and eight parameter versions of the new model were all excellent fits to the data (P 〈 0.001, R2 〉 0.99), with the eight parameter version being slightly the best. All parameters can be interpreted in biological terms; three define threshold temperatures, three define the curvilinear slopes in the model over different temperature ranges, one is a weight exponent and one is the maximum daily energy intake of a 1 g trout. The simpler six parameter model was adequate at temperatures above 7 °C.4. An additional experiment with twenty-eight trout feeding on six different invertebrate foods provided estimates of energy intake that were very similar to those predicted from the model. However, when daily intake was converted to dry weight, agreement with values from the model (also as dry weight) was poor. Possible reasons for this are discussed, as are other studies using the earlier model, and it is shown that different conclusions can be reached depending upon whether comparisons are based on units of energy, dry weight or wet weight.

Notes: 1. Temporal variation in the spatial aggregation of the freshwater bivalve Elliptio complanata was studied at a sandy site in an oligotrophic lake over three years.2. Epibenthic populations varied in aggregation over the season bringing animals closer together during spawning. The complex link between movements of mussels and aggregation dynamics suggested a functional reproductive role for horizontal locomotion of unionid mussels in lentic systems.3. The rate of locomotion did not differ systematically among males, females or hermaphrodites, and was independent of gravidity, whether compared during spawning, after spawning or throughout the ice-free season.4. In spite of the high reproductive output of mussels and the energetic cost of locomotion, no relationship was found between the rate of movement of spawning gravid mussels and reproductive output.

Notes: 1. Two sampling techniques were used to characterize invertebrate communities in eight, low-order streams along an altitudinal gradient in Costa Rica that represents the last continuous tract of primary forest spanning such extremes in elevation (i.e. near sea level to 2900 m a.s.l.) along the Caribbean Slope of Central America. A standard Surber sampler was used to sample invertebrates on the stream bottom, and drift sampling nets were used to sample invertebrates drifting in the stream flow.2. Sites were established at 30, 50, 700 1800 and 2700 m a.s.l. In one to two streams per site, six Surber samples were collected, and drift was sampled every 3 h over one 24-h period between April and August 1994. All sites were in primary forest, with the exception of the lowest elevation site (30 m) which was located in banana plantations.3. Both sampling techniques indicated that Diptera (Chironomidae) and Ephemeroptera were the dominant insect groups at all sites. Disturbed streams draining banana plantations were dominated by Chironomidae and had lower taxon richness and diversity than other sites.4. While data from benthic samples indicated that insects were the major faunal component (〉 90%) at all sites, drift samples were dominated by larval shrimps (〉 50%) at the 30 m and 50 m sites.5. Drift periodicity of invertebrates was observed at those sites characterized by predaceous fishes: nocturnal drift densities were higher than diurnal densities at 30, 50 and 700 m a.s.l., however, no periodicity was observed at 1800 and 2700 m a.s.l. where fish were absent.6. This study shows the importance of measuring invertebrate drift, in addition to directly sampling the benthos. Drift sampling provided data on a major community component (shrimps) of lowland tropical streams, that would have been overlooked using traditional benthic sampling techniques, and in some cases provided additional information on taxon richness.7. Based on results of the present study, it is recommended that drift sampling be included as a standard complementary tool to benthic sampling in biological assessments (e.g. bioassessment protocols) of tropical streams, which are often characterized by migratory invertebrate species such as shrimps. Drift samples provide critical information on the presence or absence of shrimps and also on the timing and magnitude of their migration which is an important link between many tropical rivers and their estuaries.

Notes: 1. Lough Neagh is a large eutrophic lake covering 387 km2 with a mean depth of 8.9 m. It is an important natural resource, being the largest single source of potable water for Belfast, Northern Ireland.2. This report examines the causes of the year-to-year variation in the April–June (spring) algal biomass, measured as chlorophyll a, for the period 1974–92.3. The spring chlorophyll a declined following the introduction of a phosphorus (P) reduction programme at major sewage treatment works in 1981. However, since 1990 the chlorophyll a concentrations in the spring have increased.4. Time series methodology was employed to develop a model which explained 76% of the annual variation in spring chlorophyll a concentrations.5. The independent variables used in the multiple regression model were the previous year’s spring chlorophyll a concentration, soluble reactive P inputs for April–June and the particulate P concentration in the Lough during the previous summer.

Notes: 1. Variations in the relative biovolumes of dominant cyanobacterial taxa were evaluated in the context of environmental conditions using canonical correlation analysis (CCorrA) and Redundancy Analysis (RDA). The objective was to test a conceptual model in which underwater irradiance determines dominance by bloom-forming (high light adapted) or non-blooming (low light adapted) taxa.2. The data set consisted of 404 contiguous observations, collected over a 3-year period at eight pelagic sites, in shallow Lake Okeechobee, Florida, U.S.A. Data included species biovolumes, total phosphorus (TP), total nitrogen (TN), dissolved oxygen (DO) and chlorophyll a concentrations, as well as two indices: underwater irradiance (Secchi depth) and the ratio of Secchi:total depth.3. The first environmental canonical variable was strongly correlated with the two light-related indices, and negatively correlated with TP. This reflects the predominant role of resuspended P-rich lake sediments in controlling underwater irradiance in the shallow lake. The first species canonical variable displayed a strong negative correlation with Lyngbya limnetica and L. contorta, and positive correlations with Anabaena circinalis, Aphanizomenon flos aquae and Microcystis spp. The results support the conceptual model; the first pair of canonical variables explained 55% of the variation in the species–environmental data set. RDA results provided further support for the hypothesis that irradiance was the major force controlling community structure.4. One unexpected result was a positive association between Oscillatoria spp. dominance and indicators of high irradiance. This conflicts with past research indicating that Oscillatoria is a low light adapted taxon, and the finding that it is the most abundant taxon in Lake Okeechobee. This may reflect the fact that the two Lyngbya taxa were more strongly associated with low light conditions than Oscillatoria. CCorrA results indicated that Oscillatoria densities are strongly controlled by water temperature. There is a need for more detailed studies of cyanobacteria ecophysiology in order to explain fully the seasonality of phytoplankton in this and other shallow subtropical lakes.

Notes: 1. Ten of the leading journals in the field of freshwater ecology were identified using the Science Citation Index’s Journal Citation Reports. These journals were surveyed to assess the levels and patterns of collaboration in research initiatives in regions of the Third World. Membership demographics of five professional societies in this field were also examined to elucidate distribution patterns of practitioners in the field.2. In total, 8960 papers were surveyed, of which only forty were published in a language other than English. Senior authors came from 114 of the 130 different countries listed among authors’ addresses. Of these, forty-five were from Third World countries and sixty-nine from the First World. Five countries were responsible for 60.64% of the papers submitted; the United States = 25.65%; Canada = 11.55%; Australia = 10.15%; the United Kingdom = 6.73%; New Zealand = 6.56%. Multi-authored papers accounted for 73.05% of all papers.3. Papers by authors from Third World countries accounted for only 10.93% of single-author papers and less than 10% of multi-authored papers. Collaboration was found in 73.05% of the papers surveyed, the vast majority of which (87.39%) was between authors from First World countries. Only 825 (9.21%) of the papers surveyed involved authors from different countries. Most of this collaboration (72.36%) was between authors from different First World countries.4. Some 1038 papers surveyed included research undertaken in, or included authors from, Third World countries. The majority of these papers (69.08%) were submitted by authors from Third World countries, involving either multiple or single authorship. The third most common publication relating to research in Third World regions (17.4%) came from single-author papers in which the authors were from a First World country. Only four of the papers surveyed were submitted by single authors from Third World countries working in First World countries.5. There is a disproportionate representation of taxonomic (20.3%) and marine (10.5%) papers from the Third World regions in comparison to both lentic (8.0%) and lotic (7.4%) papers.6. Membership demographics of the professional societies surveyed continue to reflect the historical origins of freshwater ecology. More than 80% of members in the three largest societies examined are registered in Europe and North America, while membership of the remaining societies remains largely regional.7. It is argued that present levels of collaboration and technology transfer from the First World to the Third World are inadequate and that, given the widening gulf in terms of personnel and resources, the future of essential research on inland waters in the Third World does not bode well unless in situ capacity building within Third World countries becomes a target of First World research and funding agencies.

Notes: 1. The relationships between body length and dry weight were examined for eight species of freshwater planktonic crustacea common in Japan: Eodiaptomus japonicus, Acanthodiaptomus pacificus, Daphnia galeata, D. similis, D. magna, Scapholeberis mucronata, Simocephalus exspinosus and Bosmina longirostris.2. The relationships of two diaptomid species were similar and the approximate equation was lnW = 2.7 + 2.6*lnL, where L is prosome length (mm) and W is dry weight (μg). The carapace length–dry weight relationships in branchiopods were more variable, with the slope ranging from 1.9 to 2.9 and the intercept from 2.0 to 3.7.3. The effects of food conditions on the relationship were examined in the laboratory, and the seasonal changes in the field were also studied.4. Practical advice is presented for predicting crustacean weight from body length.

Notes: 1. This experiment studied the effects of differing levels of the complexity of substratum architecture at two spatial scales on the distribution and abundance of benthic algae and invertebrates, and the strength of the trophic interaction between invertebrate grazers and algae. Some estimates of the effects on invertebrate colonization rates were also made.2. Four levels of microhabitat architectural complexity were created using artificial substrata (clay tiles) and placed in Mountain River, Tasmania, in two riffle types (bedrock and boulder-cobble) of differing large-scale substratum complexity. After a colonization period, invertebrate grazers were removed from half the tiles to measure the effects of grazing. Invertebrates on the tiles were also counted and identified. At the end of the experiment, algae were removed from the tiles and analysed for chlorophyll a.3. Invertebrate grazers did not reduce algal biomass during the experiment, and microhabitat-scale architecture influenced algal biomass more strongly than riffle-scale architecture. Highly complex microhabitat architecture increased algal biomass by providing more surface area, but once standardized for surface area, algal biomass decreased as the complexity of microhabitat architecture increased.4. Microhabitat-scale architecture was also predominant in determining invertebrate density and the identity of the dominant grazer species. In contrast to algal biomass, invertebrate densities and species density increased with the complexity of microhabitat architecture, suggesting that refuges from flow (and possibly predation) were as important to river invertebrates as the distribution of their food source.5. Riffle-scale architecture had some effect on the colonization of two slow-moving grazer taxa, but, overall, the colonization processes of slow-moving grazers were determined mostly by the complexity of microhabitat-scale architecture.

Notes: 1. The hypothesis was tested that intermediate connectivity to a river results in propagule inputs to wetlands, whereas excessive connectivity impedes recruitment, and insufficient connectivity causes less competitive species to be eliminated, with no recruitment of new species. As a consequence, very low or very high nutrient levels should decrease species richness by selecting specialized species, whereas intermediate nutrient levels should favour the co-occurrence of species with contrasting nutrient requirements.2. Among cut-off channels with high sinuosity and which are infrequently flooded by the river (low flood scouring), one example possesses high species richness because most species are saved from extinction by long-term isolation of the channel and cold groundwater supplies. Other channels are poorly supplied with groundwater and show a lower richness of species, because of low propagule inputs and low recruitment potential.3. Cut-off channels with low sinuosity and which are flooded at intermediate frequencies were divided into three groups. The first group was species-poor, being closely connected to the river through downstream backflows which maintain nutrient-rich and turbid waters, in keeping with the hypothesis. The second group presents intermediate richness caused by: (i) lower river backflows; and (ii) floods that partly scour substrate and plants, and afford regeneration niches for transported propagules. The third group was species-poor because of excessive groundwater supplies, which probably acted as a limiting factor for species growth and recruitment.4. The most frequently flooded channel shows the highest species richness, and occurrence of rare and fugitive species, because of floods which compensate competition by scouring sediments and plants, and afford regeneration niches for propagules. In this case, conservation of biodiversity necessitates propagule sources at the level of the river landscape.

Notes: 1. In a set of life-table experiments, cohorts of neonate Daphnia pulex were exposed to a toxic strain of Anabaena affinis and A. flos-aquae, and to a pure cyanobacterial toxin (anatoxin-a), at 12 or 14, 19, and 25 °C. The fecundity and survival of individual animals were assessed at 1-, 2- or 3-day intervals, depending on the temperature, through to the fifth brood of the control cohort. The sensitivity of D. pulex to the cyanobacteria and the toxin at each temperature was measured by determining its finite population growth rate (λ) in an experimental treatment as a fraction of that in a control treatment. Tests with three concentrations of cyanobacteria (1.0, 2.5 and 5.0 μg mL–1) and one concentration of anatoxin-a (1 μg mL–1), and with two clones of D. pulex, showed a consistent and statistically significant pattern of increasing sensitivity at higher temperatures.2. Anabaena affinis affected both survivorship and fecundity, while A. flos-aquae and its toxin, anatoxin-a, primarily affected fecundity. Presence of cyanobacteria affected brood size, brood number, time to first reproduction and interclutch interval. Temperature affected time to first reproduction and interclutch interval at all concentrations of cyanobacteria. Brood number and brood size were little affected by temperature except at the highest concentrations of cyanobacteria. Increasing the concentration of A. flos-aquae affected demographic parameters, especially at the lower temperatures, while increasing the concentration of A. affinis had less effect.3. The study suggests that increasing water temperatures in natural systems should exacerbate the inhibitory effect of toxic cyanobacteria on daphniid population growth rates.

Notes: 1. Dippers were surveyed along seventy-four acid-sensitive streams in upland Wales in 1984 and again in 1995. At forty-eight of the sites, and in an additional twenty-three to twenty-nine adjacent catchments, changes in acid-base status and macroinvertebrate communities were assessed. River habitat surveys (RHS) and GIS (Geographical Information System) provided information on habitat features.2. pH means across all the sites were higher on average by 0.12 pH units in 1995 than 1984, accompanied by significantly increased total hardness and reduced sulphate. However, geometric mean aluminium concentrations increased significantly, while the abundances of important dipper prey either remained constant (Ephemeroptera) or declined (Trichoptera; Plecoptera).3. As in 1984, dipper distribution in 1995 was related to acid-base status: aluminium concentrations were significantly higher, and pH significantly lower, at sites where dippers were absent. In both surveys, there were significantly more bankside broadleaves and fewer conifers where dippers were present.4. Although dippers occurred in 1995 on a similar number of streams as in 1984, there were both gains and losses, and an overall significant reduction in the number of visits on which birds were recorded (= registrations) per survey reach. Gains and losses were not related to habitat structure or acid-base status, and might be stochastic. Mean aluminium concentrations increased more (P 〈 0.06) at sites where dipper registrations fell, than where they increased, but changes were large enough to explain altered occupancy at only five sites. Plecopteran abundances declined most at sites losing birds.5. We conclude that recovery from acidification has not yet been large or sustained enough to allow widescale increase in the Welsh dipper population, and continued decline cannot be excluded. There is a need for better understanding of how recovery processes will permeate foodwebs to reach top predators in acidified streams, and of the geographical scale of recovery required to increase populations in dispersed organisms such as birds. Such uncertainties, together with the mismatch in trends revealed by stream chemistry and dippers, illustrate reasons why chemical data alone are inadequate for the assessment of changing river quality.

Notes: 1. Mitochondrial DNA sequence analysis was used to investigate the phylogeographic structure among populations of the amphipod Gammarus lacustris isolated in high altitude lakes from the Northern to the Southern Alps, and to investigate the historical and demographic events that may have accompanied this differentiation.2. The comparison of a 376-base segment of the mitochondrial cytochrome c oxidase I gene in fifty-four specimens from nine different populations reveals no variation within populations. However, northern populations appear divergent from those from the Southern Alps. A particular population, located at the limit between the Northern and Southern Alps shows an intermediate haplotype related to the southern lineage.3. Consideration of the different mitochondrial lineages, together with geographical differences among populations, suggests a scenario for the post-glacial colonization of G. lacustris in the alpine lakes.

Notes: 1. In this study, sediment chlorophyll profiles at twenty littoral stations in three oligo-mesotrophic lakes were compared to test whether the vertical distribution of chlorophyll is related to site characteristics (light availability, temperature, physical disturbances) and whether these profiles differ between shallow and deep portions of the littoral zone.2. The magnitude of chlorophyll peaks at the sediment surface did not vary with light intensity. Chlorophyll peaks in the shallow littoral zone had a weak tendency to decrease with increasing effective fetch. The magnitude of chlorophyll peaks at deeper sites was more closely related to water temperature than to substrate slope.3. High chlorophyll concentrations were measured down to 1–3 cm in the sediments, both at shallow (〈 2.5 m) and deep (4–10 m) stations. The depth to which high chlorophyll was found in sediments did not vary with effective fetch or sediment water content, two indices of wave disturbance in the shallow littoral zone, or with substrate slope, an index of sediment stability in the deep littoral zone. Sediment mixing is apparently not related to common indices of physical disturbances.4. Between 8 and 100% of sediment surface chlorophyll was ‘retained’ 4–5 cm into the sediments. The proportion of chlorophyll ‘retained’ in littoral sediments increased with increasing depth, increasing lake productivity (total phosphorus concentration) and increasing lake pH.5. Among-core variability (standard error/mean) in chlorophyll concentration at the sediment surface ranged from less than 1% to 33% at different stations and was highest at shallow, exposed sites. These levels of variability are similar to those found in other periphytic communities.

Notes: 1. Controls to reduce loadings of primary nutrients to maintain biotic integrity in rivers and streams have not been widely implemented because the relation between nutrients and chlorophyll, and its consequences for higher trophic levels, is confounded in lotic ecosystems by their openness, the variable degree of nutrient limitation and by the effect of physical factors.2. The relationship between primary nutrients and biotic integrity in rivers and streams was tested using biological, physical and chemical information collected since 1982 from similar locations in streams throughout Ohio using standard procedures.3. There was a negative correlation between nutrients, especially total phosphorus, and biotic integrity. The deleterious effect of increasing nutrient concentration on fish communities in low order streams was detectable when nutrient concentrations exceeded background conditions (total inorganic nitrogen and phosphorus 〉 0.61 mg L–1 and 0.06 mg L–1, respectively).4. These results suggest that the control of release of toxins and oxygen-demanding wastes to rivers is insufficient to protect aquatic life, and confirm the importance of non-point sources of pollution in catchment planning as well as the combined effect of habitat and riparian quality on nutrient assimilation.

Notes: 1. Three series of field experiments with different zooplankton species composition and biomass were performed in a small lake in the south Andes. We attempted to measure the responses of phytoplankton species resulting from grazing mortality and stimulation of growth by nutrient recycling.2. Nanoflagellates contributed substantially to total phytoplankton cell abundance. Chrysochromulina parva represented 93.4%, 92.2% and 95.9% of total phytoplankton density in December, January and February, respectively. This fraction was reduced in all treatments with increasing zooplankton biomass.3. A negative relationship was obtained between C. parva cell numbers and increase in dissolved P. On the other hand, a significant positive relationship between the abundance of the diatom Aulacoseira granulata and P concentration was observed. These results indicate that the ungrazed diatom was able to capitalise on the increase in nutrient availability.4. As a net result of the increase or decrease of algal species we observed a change in the nano:net phytoplankton relationship. The outcome of three-day incubations with increased zooplankton biomass was an increasing importance of net phytoplankton.5. The results indicate the importance of the indirect effects of zooplankton (through nutrient recycling) in the increase in diatoms, and the role of grazing as a growth-limiting factor for the flagellate C. parva.

Notes: 1. Pampulha Lake has undergone rapid eutrophication. Annual maxima of total phosphorus and conductivity increased steadily from 1993 to 1996. Nitrogen quickly decreased after macrophyte removal in 1994, but increased again in the following years2. The zooplankton was dominated by Daphnia gessneri, D. laevis, Diaphanosoma birgei and Thermocyclops decipiens. The biomass of major zooplankton organisms, including Daphnia and rotifers, increased during the period covered in this study.3. Autocorrelation coefficients have confirmed the existence of recurrent seasonal patterns for both chemical and biological variables.4. Daphnia, calanoid copepods and rotifers showed clear and recurrent seasonal patterns. Cyclopoid copepods and Diaphanosoma had temporal patterns more affected by long-term trophic changes. Other organisms such as Moina, Ceriodaphnia and Bosmina exhibited high temporal variability with no recurrent patterns.5. There was a strong and positive correlation between total phosphorus and Daphnia biomass. Seasonal patterns of this cladoceran were also inversely associated with sestonic C:P ratios. Thus, Daphnia may be limited primarily by phosphorus and not by total food availability as expressed by particulate carbon.6. This study suggests that increasing eutrophication has changed the structure as well as seasonal patterns of the zooplankton community in Pampulha Reservoir.

Notes: 1. An acoustic doppler velocimeter (ADV) was used to collect velocity data in three dimensions in front of and in the wakes of selected boulders in a riffle, where macroinvertebrates were also sampled.2. Shear stress was calculated from the covariance of downstream and vertical velocity fluctuations.3. Velocities, shear stress and turbulence measured at three points above the bed in the front and wake regions of riffle boulders were consistent with predicted patterns of flow around isolated roughness elements. There was a significant difference in mean velocities, but not near-bed velocities between front and wake regions. At 5 mm above the bed, velocities in both front and wake regions were greatly reduced, relative to the mean velocity (at 0.4 × total depth). Flows at the bed were directed upstream as part of the vortex formed at the front of the boulder and as part of the recirculation occurring in the wake.4. Shear stress was highest in the vertical plane in the wake of the boulders. Turbulence intensity and turbulent kinetic energy were greatest in the wake region, in both the down-stream and cross-stream directions. However, these results were not statistically significant. Large standard errors associated with measurements within wakes indicated that wake flows are highly variable. Further research is needed to determine the most appropriate methods of analysing differences associated with such variable flow regimes.5. The benthic macroinvertebrate fauna was significantly richer and more abundant in the wakes than at the front of boulders. Classification and ordination revealed the presence of distinct front and wake benthic communities. These differences could not be attributed to velocity differences within the benthic microhabitat, because near-bed velocities were greatly reduced in both the front and wake regions. The fauna may be responding to the highly variable turbulent regime of the wake and associated effects, such as increased deposition of particulate organic matter and exchange of dissolved gases.6. Despite the complex flow patterns inherent in natural streamflow, a large roughness element (boulder) appears to predominate in determining microflows within in its immediate surroundings. The design of some benthic sampling programs (e.g. for biomonitoring) may need to incorporate hydraulic microhabitat considerations.7. The fine-scale field measurements obtained with the ADV indicate that experimental determination of the role of turbulence in the ecology of stream benthos is now both possible and desirable.

Notes: 1. The persistence of effects of sediment resuspension on chlorophyll a, phytoplankton production and plant nutrients was examined by artificially resuspending sediment in enclosures in three shallow lakes and monitoring concentrations for 4–8 days. Realism was assessed by relating initial suspended solids concentrations to those observed during natural wind events.2. Positive effects on the phytoplankton, persisting for at least 4–6 days were detected in eight of the nine experiments, and similar effects on nutrient concentrations were also common, although suspended solids had normally returned to control levels within 24 h3. The phytoplankton during the periods of persistence was normally dominated by planktonic rather than benthic/meroplanktonic genera.4. Several of the positive responses appeared to be associated with relief of nitrogen deficiency in the algae.5. Persistent effects from previous resuspension events may cause baseline concentrations of phytoplankton and nutrients in shallow lakes to be overestimated and the effects of resuspension on phytoplankton and nutrients to be underestimated

Notes: 1. The influence of land use and physico-chemical factors on stream macroinvertebrates was analysed at fifteen sites over a 2-year period in a single conifer-afforested catchment in Ireland, in an area subject to very low levels of atmospheric pollution.2. Macroinvertebrate assemblages were classified using two-way indicator species analysis into five major groupings that were related to distance from headwaters and land use. Trends in macroinvertebrate community composition were related to changes in physico-chemical and biotic characteristics of the river and its tributaries using canonical correspondence analysis.3. Local ecological factors (e.g. acid water, moss, shading or agricultural runoff), longitudinal trends in stream physico-chemistry (related to distance from headwaters, geology and land use) and season (related to life history patterns of the invertebrates) were the explanatory variables of spatio-temporal patterns in macroinvertebrate community composition in the catchment.4. Spatial variation in macroinvertebrate density, taxon richness, diversity and evenness was investigated in relation to environmental characteristics of the study sites using Spearman’s rank correlation, principal components analysis and stepwise multiple regression. Invertebrate density and richness increased with distance from the headwater and associated increases in pH, water hardness and nutrients. Macroinvertebrate density and richness also increased with increasing moss weight. Invertebrate diversity and evenness increased with shading of the channel.5. The increase in macroinvertebrate density and richness and changes in community composition were particularly marked over a relatively short (1.2 km) distance in one tributary, and were concurrent with a rapid increase in stream pH of 1.7 units.6. Although macroinvertebrate communities at conifer-afforested sites were not impoverished in the same way as those in some other parts of Europe, they differed from the communities found above and below the plantation. This appeared to be owing to the primary importance of local ecological factors and the effect that the longitudinal position of these forest sites within the river system had on their physico-chemical and biotic nature.

Notes: Ichnofabric in the Upper Cretaceous Sego Sandstone and Anchor Mine Tongue of east-central Utah can be differentiated into two components: (1) discrete Ophiomorpha and (2) mottling and other trace fossils. The ichnofabric index method was employed to evaluate spatial variability of the ichnofabrics within depositional sequences and component systems tracts. Indices were logged for amount of bioturbation caused solely by Ophiomorpha (Oii) and that represented by all other biogenic features (Bii). Values of Oii〉  1 are more pervasive in lowstand systems tracts compared to transgressive systems tracts. This is consistent with the predominance of marginal and nearshore marine, sand-dominated settings that are characteristic of lowstands, which are favourable habitats for colonization by Ophiomorpha producers. Ichnofabric index values vary both vertically and laterally within any given systems tract, reflecting differences in physical and biological parameters operating in the palaeoenvironment. These parameters include the total number and behaviours of organisms occupying the substrate, as well as substrate texture and grain size, and rates of sedimentation. The architectural style of Ophiomorpha was examined within five depositional facies: shelf, storm deposit, lower shoreface, shoreface, and estuarine. Inclinations of individual burrow elements were approximated relative to bedding planes, categorized as either vertical, inclined or horizontal, and then plotted on ternary diagrams. Based on the types of facies present, these results suggest that variations in the geometric configurations of Ophiomorpha are controlled primarily by physical energy levels, and the rate and nature of sedimentation. Results of this study have broad implications for understanding the physical factors affecting facies variability within sequences and systems tracts. When coupled with sedimentologic data, recognition of variations in the distribution of ichnofabrics and architectural style of Ophiomorpha can provide additional information useful for characterizing depositional environments, and therefore could be integrated with other basin analysis techniques to test and refine sequence stratigraphic interpretations.

Notes: The morphology of the source area of the Canary Debris Flow has been mapped using both GLORIA reconnaissance and TOBI high-resolution sidescan sonar systems. West of ≈19°W, the seafloor is characterized by a strongly lineated downslope-trending fabric. This fabric can be interpreted as being caused by streams of debris separated by longitudinal shears. Multiple flow pulses are indicated by a series of asymmetrical lateral ridges which mark the northern boundary of the flow. East of ≈19°W, GLORIA data show only a weak fabric of irregular patches and alongslope lineaments. The TOBI data show the patches to be coherent sediment blocks up to 10 km across, surrounded by debris flow material. These are interpreted as in situ areas of seafloor sediment which have survived the slope failure and debris flow event rather than transported fragments of a failed sediment slab. TOBI data from the best developed area of alongslope lineaments show a series of small faults downstepping to the west. This area of seafloor is interpreted as one of partial sediment failure, where the failure process became ‘frozen’ before total mobilization of the seafloor sediments could occur. The overall morphology of the failure area indicates removal of a slab-like body of sediment, although we cannot distinguish between retrogressive and slab-slide failure mechanisms. If the latter mechanism is applicable, fragmentation of the failing ‘slab’ must have commenced concurrently with the onset of downslope transport. Immediately upslope from the debris flow source area, a seafloor of characteristic rough blocky texture is interpreted as the surface of a debris avalanche derived from the slopes of the island of El Hierro. The debris flow and avalanche appear to be simultaneous events, with failure of the slope sediments occurring while the avalanche deposits were still mobile enough to fill and disguise the topographic expression of the debris flow headwall. Loading of the slope sediments by the debris avalanche most probably triggered the Canary Debris Flow.

Notes: Gypcretes of Miocene age are preserved beneath a 9·53 ± 0·36 Ma ignimbrite along the eastern margin of the Oligo-Pleistocene Calama Basin, northern Chile. They are restricted to a single stratigraphic horizon developed within laterally extensive (〉35 km) coalesced alluvial fan deposits, developed along the margin of an endorheic basin. Two types of gypcrete are recognized. Type 1 comprises almost completely gypsum-cemented sandstones containing alabastrine nodules and columns, sub-vertical and horizontal veins of fibrous gypsum and ‘v-shaped’ cracks infilled by clastic material, and are interpreted as surface weathered gypsic crusts. Type 2 gypcretes are composed of massive, reddened poikilitic and mesocrystalline gypsum (up to 80% of the rock) with isolated bedding-parallel, clast-rich lenses (200 × 30 cm) and sub-vertical veins of fibrous gypsum. The massive texture resembles that of well developed B horizons in Quaternary alluvial desert soils. The crystal forms suggest an origin as a subsurface gypsic crust formed by a combination of hydromorphic (poikilitic) and illuvial (mesocrystalline) processes with the fibrous gypsum veins suggestive of periodic surface exposure.Gypcrete horizons are up to 25 m thick and composed of both gypcrete types. They represent superimposed phases of surface and subsurface gypcrete development. Quaternary gypcretes are developed in arid climatic regimes, but are not considered to develop under hyper-arid climates. An arid climate is considered to have prevailed in the study area up to 9·5 Ma after which a change to hyper-aridity favoured gypcrete preservation.

Notes: Palaeokarst is an important feature of late Dinantian exposure surfaces. Soil-filled depressions are widely developed. These are comparable to modern day solution dolines and were probably interspersed by areas of relatively bare limestone pavement. The palaeokarst primarily exhibits a smooth, mamillated to potholed surface form, consistent with its formation beneath a soil cover. Areas between the depressions have been extensively stylolitised and would likely have originally been characterized by small-scale fretted and sculpted karren forms typical of subaerial karstification. Palaeokarst pits making up the depressions are thought to have been initiated through stem-flow drainage from trees. Rain water, intercepted by the crown of the tree, was concentrated at specific sites on the emergent surface and dissolution beneath the trunk produced cylindrical pits that propagated vertically downwards. Trees responsible for concentrating drainage may also have enhanced the acidic nature of the rain water through leaching of organic acids from foliar and woody tissues. Downward propagation of the pits was limited to the uppermost 1–2 m and enlargement primarily occurred through lateral amalgamation of adjacent pits. Once initiated, continued development of the depressions would have been self perpetuating; the preferential accumulation of volcanic ash and organic matter enhancing water retention and encouraging further vegetation growth. In contrast, intervening areas would have been characterized by slow vertical denudation only. Karstification likely took of the order of a few hundred years in the case of potholed palaeokarstic surfaces formed solely by stem-flow drainage, to a few tens of thousands of years where the palaeokarst is more mature.

Notes: Sand-filled cracks from the Lower Fine-grained Quartzite of Dalradian (late Proterozoic) age on the Island of Islay, western Scotland, may be divided into two main types, both of which form orthogonal and non-orthogonal closed patterns on bedding surfaces. Type 1 cracks are short and lenticular in cross-section, contain sand which had been injected downwards, and are found on the bottoms of cross-laminated sandstone beds. Type 2 cracks cut several beds and preserve evidence of upward flow of water-saturated sand. Both types of crack developed through the interstratal intrusion of water-saturated sand into shrinkage cracks in mud or muddy sand, not, as previously thought, as a result of sub-aerial desiccation, or sub-aqueous cracking of the sediment surface (synaeresis). These cracks likely resulted from layer-parallel contraction caused by compaction of mudstone layers during burial. Seismic shock may have provided the trigger for the preferential development of polygonal crack patterns in these layers instead of the more usual small-scale dewatering structures. From a detailed comparison with published descriptions of filled cracks from a number of different geological environments, it is concluded that interstratal cracking is a mechanism which rivals sub-aerial desiccation in importance, and is more common in the geological record than is currently realized.

Notes: Late Pleistocene travertines up to 40 m thick near Rapolano Terme in Tuscany, central Italy, were precipitated by hot water issuing from springs on hillsides and flowing into adjacent depressions to mix with rainwater. Proximal light-coloured slope and terrace travertines pass distally into darker reed mound and depression-fill travertines. Lithotypes include crystalline crust, shrub, pisoid, paper-thin raft, coated bubble, reed, and lithoclast-breccia. High precipitation rates resulted in rapid slope aggradation and progradation. Dilution by rainwater likely lowered precipitation rates in depressions, but deposition was augmented by allochthonous material eroded from upslope travertines.Slope Depositional Systems consist of Smooth and Terrace Slope facies characterized by white crystalline crusts, with diverse additional lithotypes in terrace pools. Depression Depositional Systems have mixed light and dark travertines with horizontal to gently concave stratification. Extensive light-coloured Shrub Flat travertine is dominant; darker Marsh-Pool Facies composed of fine lithoclast and reed travertine is localized. Reed Mounds composed of mixed light and dark travertines localized by abundant reed growth, formed where spring water emerged near the bases of low angle slopes.Distal reduction in accretion rate was the major influence on sequence development. Light-coloured slope travertines interdigitate with darker depression deposits. Vertical aggradation of slope deposits, mound progradation, and filling of topographic depressions is expressed by advance and retreat of facies. Evolution from depression to slope or mound sequences is termed ‘steepening up’. Up-sequence change from slope or mound to depression facies is termed ‘levelling up’. Exposure surfaces associated with palaeosols are common in all facies and often constitute sequence boundaries. They are more closely spaced in depression sequences, reflecting slower and possibly also more discontinuous accumulation at sites furthest from hot springs.

Notes: The Palaeocene–Eocene sequence on the Komandorsky Islands is represented by sediments and minor volcanics with a total thickness of more than 3000 m. Sandstone, siltstone, mudstone, siliceous rocks and conglomerate, which have accumulated in the upper and middle parts of a deep-water fan, prevail. All the debris was delivered from the north-east, from the side of the contemporary Komandorsky basin in the Bering Sea. Products of volcanic denudation and fresh tephra dominate its composition. However, at some levels the sandstone contains fragments of jasper, quartzite, slate, schist, gabbro and granite as well as non-volcanic quartz along with a volcanic component. The heavy minerals fraction of the sandstone contains considerable quantities of apatite, zircon, garnet and chromite, as well as pyroxenes, amphiboles and magnetite. The chemical composition of the garnet is specific to metamorphic rocks. A significant admixture of chromite is indicative of denudation from an ophiolite complex. The folded and partly metamorphosed pre-Palaeogenic rocks were a source of these fragments. Their most likely source terrane was the Shirshov-Bowers chain (Cretaceous palaeoarc). The Komandorsky block originally was the forearc part of the Aleutian arc where the latter was superimposed on the Shirshov-Bauers chain. A subsequent north-west displacement of forearc structures, in response to the transform fault at the boundary between the Pacific and North American plates, could have resulted in the separation of the Komandorsky block from its Early Palaeogene debris source area.

Notes: Field and petrographic investigations of Holocene evaporites in the Ras El Shetan area, Gulf of Aqaba, Egypt, indicate the presence of microbial mats either in the form of laminites or stromatolites. The morphology of microbial mats and gypsum crystal size characterize the following lithofacies: (1) slump-stromatolitic gypsarenite, (2) random gypsrudite, (3) stromatolitic gypsarenite, and (4) microbially laminated gypsrudite. These evaporite lithofacies are formed above pre-evaporitic mudstones rich in disrupted cyanobacterial filaments, burrows and cerithid gastropods. The morphology of the gypsum crystals is mainly lenticular, indicating enrichment of dissolved organic compounds in the depositional environment. The difference in size of the lenticular gypsum crystals is related to minor changes in salinity and temperature of the parent brine. Fluid inclusions in gypsum crystals indicate their formation at low temperature (〈50°C) in a seawater sourced brine that evaporated to gypsum saturation or higher. The brine salinities range from 10·62 to 12·99 equivalent wt% NaCl, and the brine densities range from 1·08 to 1·11 g/cm3. The change in morphology of the microbial mats (stromatolites and laminites) is related mainly to changes in water depth, from a very shallow salina to a coastal sabkha. Lenticular gypsum nucleated displacively in the microbial mats from saline, oxygenated groundwater that seeped from the sea through a barrier.

Notes: Lacustrine laminated sediments (laminites) present in Late Miocene formations of the Híjar Basin, SE Spain, display well developed loop bedding, a structure consisting of bundles of laminae that are sharply constricted at intervals, giving a morphology of loops or links of a chain. The laminite sequences, which are interbedded with turbidite marlstones, were accumulated on the bottom of a permanently stratified lake developed in a rapidly subsiding basin limited by 010° and 105° normal faults. As deduced from both macro- and microdeformational analyses, the basin evolved under an extensional stress field throughout the Late Miocene. Four main types of loops, simple and complex loops with subcategories, have been recognized within the laminite sequence. Simple loops of type 1 show the best definite pattern, quite similar to ‘pinch and swell structures’, a type of boudinage typical of stretching of alternating beds where the competence contrast is not strongly marked. The remaining loop types display contortion and occasional breakage of laminae (microfaulted edges) indicative of microdeformation near the boundary between the ductile-brittle deformational fields. The distribution of the various loop types across the laminite sequence reflects an interplay between progressive lithification of the laminites as sedimentation progressed and tectonic stresses which affected the sediment sequence. Accordingly, a mechanism of deformation under an extensional stress field, ultimately related to the creep movement of the main basin faults which resulted in successive seismic shocks of low magnitude, is proposed to explain the formation of loop bedding in the laminites.

Notes: Late Miocene platform carbonates from Nijar, Spain, have been extensively dolomitized. Limestones are present in the most landward parts of the platform, in stratigraphically lower units and topographically highest outcrops, suggesting that dolomitizing fluids were derived from the adjacent Nijar Basin. The dolomite crystals range from 〈10 to ≈100 μm existing as both replacements and cements. Na, Cl and SO4 concentrations in the dolomites range from 200 to 1700 p.p.m., 250–650 p.p.m., and 600–7000 p.p.m., respectively, comparable with other Tertiary and modern brine dolomite values, and also overlapping values from mixing-zone dolomites. Sr concentrations range between 50 and 300 p.p.m., and the molar Sr/Ca ratios of dolomitizing fluids are estimated to range between 7× seawater brine to freshwater ratios. The δ18O and δ13C of the dolomites range from −1·0 to +4·2‰ PDB, and −4·0 to +2·0‰ PDB, respectively. 87Sr/86Sr values (0·70899–0·70928) of the dolomites range from late Miocene seawater to values greater than modern seawater.Mixtures of freshwater with seawater and evaporative brines probably precipitated the Nijar dolomites. Modelled covariations of molar Sr/Ca vs. δ18O and Na/Ca vs. δ18O from these mixtures are consistent with those of the proposed Nijar dolomitizing fluids. Complete or partial dolomite recrystallization is ruled out by well preserved CL zoning, nonstoichiometry and quantitative water–rock interaction modelling of covariations of Na vs. Sr and δ18O vs. δ13C. The possibility of multiple dolomitization events induced by evaporative brines, seawater and freshwater, respectively, is consistent with mineral-mineral mixing modelling.The basin-derived dolomitizing brines probably mixed with freshwater in the Nijar Basin or mixed with fresh groundwater in the platform, and were genetically related either to deposition of the Yesares gypsum or the Feos gypsum. Dolomitization occurred during either the middle Messinian or the early upper Messinian. Nijar dolomitization models may be applicable to dolomitization of other late Miocene platform carbonates of the western Mediterranean. Moreover, the Nijar models may offer an analogue for more ancient evaporite-absent platform carbonates fringing evaporite basins.

Notes: Foraminifera can be used to determine the source(s) of carbonate sediment and the directions of sediment transport in shallow, coastal lagoons such as Frank Sound on the south-central coast of Grand Cayman. These determinations, based on the distribution of foraminiferal assemblages and ‘tracer species’ (numerically abundant species that live in known physiographic units and/or ecological conditions), show that the lagoonal sediments are a mixture of grains that originated in the lagoon and forereef. The variable proportions of these foraminifera throughout the lagoon reflects the dynamic processes that control lagoonal sedimentation. Amphistegina gibbosa, Discorbis rosea, and Asterigerina carinata lived in the forereef environment. The fact that these ‘tracer species’ are found throughout Frank Sound and in the beach sands, shows that they were transported across the reef crest and the lagoon. Abrasion-resistant Archaias angulatus, a‘tracer species’ indicative of a lagoonal setting, forms up to 50% of foraminiferal assemblages found in the lagoonal sediments. Preferential winnowing of small tests from these populations indicates sorting under high energy conditions. The vertical distribution of the forereef and lagoonal foraminifera in the sediment blanket that covers the floor of Frank Sound indicates that these processes are temporally persistent.Transportation of forereef foraminifera into and around the lagoon and sorting of the lagoonal foraminifera cannot take place under ‘normal’ conditions when the tranquil lagoon is characterized by weak currents. Storms and/or hurricanes, however, generate short-lived high-energy events that can move and sort the sediment and foraminifera. At the height of a storm, water and sediment are moved over the reef and then piled and held onshore by the onshore winds and the constant flow of water over the reef and across the lagoon. These currents can mix some of the lagoonal and forereef sediments. As a storm wanes, however, the ‘piled water’ flows offshore via strong rip currents that pass into the ocean through the channels which transect the reef. These currents winnow and/or strip sediment from the lagoon and may transport lagoonal sediments into the forereef area. As a result, residual lagoonal sediment is commonly characterized by larger and abrasion-resistant foraminifera.

Notes: The Sydney Basin of New South Wales, Australia is a foreland basin containing a thick (up to 10 km) Permo-Triassic succession. The southern margin of the basin exposes strata deposited during Late Palaeozoic glaciation of south-eastern Gondwana. The Early Permian Wasp Head, Pebbley Beach, Snapper Point Formations and Wandrawandian Siltstone were deposited between 277 and 258 Ma on a polar, glacially influenced continental margin adjacent to ice sheets located over East Antarctica and eastern Australia. Sedimentary facies, together with related ichnofacies and fauna, can be grouped into six facies associations that record marine sub-environments ranging from high energy, storm-dominated inner shelf to turbidite-dominated upper slope settings. Cold marine conditions, with near-freezing bottom water temperatures, are recorded by glendonites. Ice-rafted debris, most likely deposited by icebergs, occurs in almost all facies associations.An allostratigraphic approach, emphasizing the recognition of bounding discontinuities (i.e. erosion surfaces and marine flooding surfaces), is used to subdivide the Early Permian stratigraphy into facies successions. Three types of succession can be identified and record changes in the relative influence of allocyclic controls such as basin tectonics, sediment supply and glacio-eustatic sea level variation.Together, sedimentological and allostratigraphic data allow reconstruction of the depositional history of the south-western margin of the Sydney Basin. Initial marine sedimentation, characterized by sediment gravity flows and storm-deposited sandstones of the lower Wasp Head Formation, occurred adjacent to a faulted basin margin. Overlying successions within the upper Wasp Head, Pebbley Beach and Snapper Point Formations, record aggradation in inner to outer shelf settings along a storm- and glacially influenced continental margin. Tectonic subsidence and basin flooding is recorded by deeper water turbidites of the Wandrawandian Siltstone.

Notes: The Schleenhain open pit coal mine, located 30 km south of Leipzig, Germany, exposes Upper Eocene and Oligocene non-marine strata representing fluvial deposition in the centre of the Weisselster Basin. Active mining and successive cuts provided the rare opportunity to obtain a three-dimensional perspective of laterally extensive surface outcrops. These were used to construct a detailed fence diagram, which provided the basis for recognition of key architectural elements in the weakly consolidated meandering stream deposits. In addition to the eight basic architectural elements of Miall (1985), the element SL (shallow lake deposits) was newly defined and the element CH (channel) was subdivided into CHg (palaeo-river system) and CHk (small channel). The profiles contain parts of two fining-upward cycles, which are separated by an unconformity spanning the Early Oligocene. Deposits of the first cycle begin with transverse sand bars (downstream accretion deposits-DA) and point bars (lateral accretion deposits-LA). The upper part of the cycle is represented by overbank fines (OF) and the element SL, which consists of laterally discontinuous lenses of dark, plant-bearing, kaolinite-rich clays, that were deposited in shallow lakes adjacent to the active channel. Coal seams interlayered with palaeosols are the main constituents of element OF. Sheetlike bodies of medium to fine gravels (gravel bars and bedforms-GB) on an erosive coal surface mark the beginning of the second cycle. Dissolution of underlying Permian salts and sulphates prior to, during, and after the deposition of the Palaeogene strata caused the development of two synclines within the outcrop. Coal seams and clay horizons which thicken and dip towards the centre of the synclines, provide evidence for their chronological development.

Notes: Aptian Lower Greensand Group exposures in the cliffs of the Isle of Wight (southern England) display a consistent coarsening-up cyclicity on the scale of centimetres to tens of metres that reflects the bed, bed-set, parasequence, parasequence set and sequence hierarchy. These coarsening-up cycles are most commonly recognized at the scale of parasequences (20 cm to 10 m thick), genetically related groups of which form parasequence sets. Both parasequences and parasequence sets contain the succession of biofacies that culminate in firmground development. Numerous episodes of erosion, deposition and colonization are recorded, reflecting multiple erosion/bypass events. The increase in mean grain-size through each cycle is reflected by changes in physical sedimentary structures; ichnofauna or bioturbational fabric; fossil fauna and diagenesis. Interbedded mudstones, siltstones and sandstones in the lower beds of each cycle display a variety of structures ranging from low-angle, hummocky, or tabular cross-strata, sandstone-filled erosional gutters and planar lamination. The cleaner sandstones found in the upper parts to each cycle are often completely bioturbated with only rare stratification and pebble/plant debris-filled scours preserved. Bioturbational fabrics change upward through each cycle from small, subhorizontal, mud- or sandstone-filled burrows to large, branching, clay-filled or cemented burrow systems. The top surface of each cycle is marked by a fossil epifauna indicative of firm to hard substrate conditions. Concentrations of bivalves, brachiopods, bryozoa, crinoids and corals are preferentially cemented by iron oxide, carbonate or phosphate. Such cements were early and thus utilized by firm or hard substrate dwellers. This fossiliferous, cemented sandstone is overlain by a flooding surface marked by the mudstone and silt-rich sandstones at the base of the next cycle. Together, the fauna and ichnofauna in each cycle represent the gradual development of firm substrate conditions, culminating in the diverse firmground fauna preserved at the top of each cycle. The fauna and changing substrate conditions reflect the hiatuses developed during successive episodes of marine flooding. High species diversity is matched by complex patterns of taphonomic feedback in the mature firmground faunas that mark major flooding surfaces. Increasing faunal maturity allows recognition of a hierarchy of hiatuses. This hierarchy is analogous to the parasequence–parasequence set division. The stratigraphic condensation of firmgrounds can be used to empirically define the condensed section, the thickness of sediment between firmgrounds being a function of sediment supply and water depth (accommodation space).

Notes: Metre-scale lithologic cycles, visible in core and on logs from Maastrichtian chalks of the Dan Field, were examined to determine their mechanisms of deposition and relation to hydrocarbon production. The lower parts of cycles consist of porous, cream-coloured, largely non-stylolitic, commonly laminated chalk with limited bioturbation (mainly escape burrows). Cycles are capped by thinner intervals of white to grey, hard, stylolitic chalk with concentrations of bioclastic material, intense burrowing and few preserved primary sedimentary structures. The cycle caps contain nearly twice as much Mg as compared to the more porous parts of cycles and also have slightly larger δ18O values (−4·1‰ for the caps; −4·4‰ for porous zones). There is a significant reduction of average cycle thickness, as well as total thickness of the Maastrichtian chalk section, from SW to NE across the Dan Field. The cycle thinning largely results from a reduced thickness of porous chalks from the lower parts of cycles and thus is reflected in lower average porosity and permeability on the NE side of the field. These data indicate that episodic winnowing removed fine-grained constituents from highstanding northeastern areas. Porous cycle bases were deposited at relatively high rates that precluded complete bioturbation; preserved laminae, coupled with escape burrows, reflect episodic sediment influx in areas that flank the seafloor highs. Cycle tops apparently accumulated more slowly (throughout the region, but especially on seafloor highs), perhaps because of reduced productivity of planktic organisms. Slower sedimentation allowed more complete bioturbation and destruction of sedimentary structures, and also led to incipient high-magnesium calcite seafloor cementation (sufficient to yield firmer sediment and enhanced burrow preservation, but not to form true hardgrounds). Thus, the elevated magnesium contents and reduced porosity of the cycle caps reflect very early diagenetic processes that were only partially modified by burial diagenesis.Rates of chalk deposition, as inferred from physical and geochemical evidence, appear to be a significant control on reservoir characteristics in North Sea chalks. The highest average porosities and permeabilities are found in areas with the highest sediment accumulation rates where seafloor diagenesis is minimized. Topographic depressions at the time of sedimentation can thus be expected to have the best production characteristics, and synsedimentary topographic highs should have the thinnest sections and the poorest petrophysical properties.

Notes: A volcaniclastic sedimentary fan extending to water depths of 4000 m is characterized using gravity cores, camera surveys, high-resolution sonar images, seismic records and bathymetry from the submarine portion of La Fournaise volcano, Réunion Island, a basaltic shield volcano in the SW Indian Ocean.Three main areas are identified from the study: (1) the proximal fan extending from 500 m water depth down to 2000 m water depth; (2) the outer fan extending from 2000 m water depth down to 3600 m water depth; (3) the basin extending beyond 3600 m water depth. Within these three main areas, seven distinct submarine environments are defined: the proximal fan is characterized by volcanic basement outcrops, sedimentary slides, deep-water deltas, debris-avalanche deposits, and eroded floor in the valley outlets; the outer fan is characterized by a discontinuous fine-grained sedimentary cover overlying coarse-grained turbidites or undifferentiated volcanic basement; the basin is characterized by hemipelagic muds and fine-grained turbidites interbedded with sandy and gravelly turbidite lobes.The evolution of the deep-sea volcaniclastic fan is strongly influenced by sector collapses, such as the one which occurred 0·0042 Ma ago. This collapse produced a minimum of 6 km3 of debris-avalanche deposit in the proximal area. The feeding regime of the deep-sea fan is ‘alluvial dominated’ before the occurrence of any sector collapse and ‘lava-dominated’ after the occurrence of a sector collapse.The main deep-water lava-fed delta is prograding among the blocks of the debris-avalanche deposits as a result of turbidity flows occurring on the delta slope. These turbidity flows are triggered routinely by wave-action, earthquakes and accumulation of new volcanic debris on top of the deltas.Both turbidity currents triggered on the deep-water delta slope, and those triggered by debris avalanche reworked volcaniclastic material as far as 100 km from the shore line.

Notes: The petrography and geochemistry of fine- and medium-crystalline dolomites of the Middle Devonian Presqu’ile barrier at Pine Point (Western Canada Sedimentary Basin) are different from those of previously published coarse-crystalline and saddle dolomites that are associated with late-stage hydrothermal fluids. Fine-crystalline dolomite consists of subhedral to euhedral crystals, ranging from 5 to 25 μm (mean 8 μm). The dolomite interbedded with evaporitic anhydrites that occur in the back-barrier facies in the Elk Point Basin. Fine-crystalline dolomite has δ18Ο values between −1·6 to –3·8‰ PDB and 87Sr/86Sr ratios from 0·7079–0·7081, consistent with derivation from Middle Devonian seawater. Its Sr concentrations (55–225 p.p.m., mean 105 p.p.m.) follow a similar trend to modern Little Bahama seawater dolomites. Its rare earth element (REE) patterns are similar to those of the limestone precursors. These data suggest that this fine-crystalline dolomite formed from Middle Devonian seawater at or just below the sea floor.Medium-crystalline dolomite in the Presqu’ile barrier is composed of anhedral to subhedral crystals (150–250 μm, mean 200 μm), some of which have clear rims toward the pore centres. This dolomite occurs mostly in the southern lower part of the barrier. Medium-crystalline dolomite has δ18O values between −3·7 to −9·4‰ PDB (mean −5·9‰ PDB) and 87Sr/86Sr ratios from 0·7081–0·7087 (mean 0·7084); Sr concentrations from 30 to 79 p.p.m. (mean 50 p.p.m.) and Mn content from 50 to 253 p.p.m. (mean 161 p.p.m.); and negative Ce anomalies compared with those of marine limestones. The medium-crystalline dolomite may have formed either (1) during shallow burial at slightly elevated temperatures (35–40 °C) from fluids derived from burial compaction, or, more likely (2) soon after deposition of the precursor sediments by Middle Devonian seawater derived from the Elk Point Basin.These results indicate that dolomitization in the Middle Devonian Presqu’ile barrier occurred in at least two stages during evolution of the Western Canada Sedimentary Basin. The geochemistry of earlier formed dolomites may have been modified if the earlier formed dolomites were porous and permeable and water/rock ratios were large during neomorphism.

Notes: Bed sediment, velocity and turbidity data are presented from a large (145 km long), generally well-mixed, micro-tidal estuary in south-eastern Australia. The percentage of mud in the bed sediments reaches a maximum in a relatively narrow zone centred ≈30–40 km from the estuary mouth. Regular tidal resuspension of these bed sediments produces a turbidity maximum (TM) zone in the same location. The maximum recorded depth-averaged turbidity was 90 FTU and the maximum near-bed turbidity was 228 FTU. These values correspond to suspended particulate matter (SPM) concentrations of roughly 86 and 219 mg l−1, respectively.Neither of the two existing theories that describe the development and location of the TM zone in the extensively studied meso- and macro-tidal estuaries of northern Europe (namely, gravitational circulation and tidal asymmetry) provide a complete explanation for the location of the TM zone in the Hawkesbury River. Two important factors distinguish the Hawkesbury from these other estuaries: (1) the fresh water discharge rate and supply of sediment to the estuary head is very low for most of the time, and (2) suspension concentrations derived from tidal stirring of the bed sediments are comparatively low. The first factor means that sediment delivery to the estuary is largely restricted to short-lived, large-magnitude, fluvial flood events. During these events the estuary becomes partially mixed and it is hypothesized that the resulting gravitational circulation focuses mud deposition at the flood-determined salt intrusion limit (some 35 km seaward of the typical salt intrusion limit). The second factor means that easily entrained high concentration suspensions (or fluid muds), typical of meso- and macro-tidal estuaries, are absent. Maintenance of the TM zone during low-flow periods is due to an erosion-lag process, together with a local divergence in tidal velocity residuals, which prevent the TM zone from becoming diffused along the estuary axis.

Notes: Side-scan sonar, seismic and core data are used to identify mega-flutes, transverse and ‘V’ shaped bedforms in turbidites around the Valencia channel mouth, north-west Mediterranean. Long-range side-scan sonar data reveal a broad, curved, asymmetric, channel, that widens and terminates downfan. The western channel bank near the channel mouth has been partly eroded by turbidity currents that spilled out of the channel. Transverse bedforms on the east of the channel floor are interpreted as antidunes and, if this interpretation is correct, they indicate that the flow was probably supercritical at least locally within the channel. Trains of mega-flutes, are incised into coarse-grained sediments of the channel floor near the channel mouth. The association of mega-flutes and antidunes is thought to be diagnostic of channel–lobe transitions on deep-sea fans. The mega-flutes pass downfan into an area of streaks that diverge at up to 45° and indicates flow expansion from the channel mouth. About 75 km downfan from the channel mouth, deep-towed side-scan data record transverse bedforms (interpreted as antidunes) passing downfan into an area covered by ‘V’ shaped bedforms with upflow pointing apices (named chevrons here). The chevrons are commonly c. 200 m from limb to limb and c. 2 m in amplitude with flow-parallel wavelengths of c. 400 m. We propose that chevrons were formed by a strong, probably supercritical (or near critical) turbidity current spreading from the channel mouth and flowing towards the Balearic Abyssal Plain. Thinning of the turbidity current, resulting from flow spreading would allow the Froude number to remain high up to 100 km from the channel mouth and could explain the observed reduction in antidune wavelength.

Notes: Intimins, encoded by eae genes, are outer membrane proteins involved in attaching–effacing (A/E) lesion formation and host cell invasion by pathogenic bacteria, including enteropathogenic Escherichia coli (EPEC) and Citrobacter rodentium. A series of intimins, harbouring specific mutations close to the C-terminus, were constructed using pCVD438, which encodes the eae gene from EPEC strain E2348/69. These mutant plasmids were introduced into EPEC strain CVD206 and C. rodentium strain DBS255, which both contain deletion mutations in their eae genes. CVD206, CVD206(pCVD438) and CVD206(pCVD438) derivatives were assessed for their ability to promote A/E lesion formation or invasion of HEp-2 cells and to induce A/E lesions on fresh human intestinal in vitro organ cultures (IVOC). The pathogenicity of C. rodentium DBS255 harbouring these plasmid derivatives was also studied in mice. Here, we report that intimin-mediated A/E lesion formation can be segregated from intimin-mediated HEp-2 cell invasion. Moreover, adherence to IVOC, EPEC-induced microvillus elongation and colonization of the murine intestine by C. rodentium were also modulated by the modified intimins.

Notes: We have isolated and sequenced a set of deletions stimulated by DNA palindromes in Escherichia coli. All of the deletions are asymmetric with respect to the parental sequence and have occurred at short direct repeats. This is consistent with deletion by strand slippage during DNA replication. The orientation of the asymmetry in such deletion products is diagnostic of the direction of the strand slippage event. It is therefore also diagnostic of its occurrence on the leading or lagging strand of the replication fork when the direction of replication is known. In all cases in which the orientation of the asymmetry could be determined with respect to DNA replication, the products were consistent with a preference for deletion on the lagging strand of the fork. The data include replication slippage in three situations: on the chromosome of E. coli, in bacteriophage λ and in high-copy-number pUC-based plasmids.

Notes: The transposon Tn5 ble gene and the Escherichia coli alkylation-inducible aidC locus are co-operatively involved in the resistance to the anti-cancer drug and DNA-cleaving agent bleomycin and enhance fitness of bacteria in the absence of the drug. In this report, we demonstrate that the aidC locus is identical to nrfGthe last gene of the nrf operon involved in the periplasmic formate-dependent nitrite reduction. In the presence of Ble, NrfG expression is specifically induced and restores both bleomycin resistance and its associated beneficial growth effect in an aidC− strain. In vitro DNA protection assays reveal that purified Ble prevents bleomycin-mediated DNA breakage, as do bleomycin-binding proteins. Similarities between haems of the cytochrome c biogenesis nrf pathway and iron bleomycin suggest a DNA repair-independent molecular mechanism for both bleomycin resistance and increased viability. The Ble protein binds bleomycin and prevents DNA breakage. It also induces the nrf locus that may assimilate bleomycin into haem for extracellular transport or inactivate bleomycin. Inactivation of potent DNA oxidants confers a better fitness to the bacterium carrying the transposon, suggesting a symbiotic relationship between host and transposon.

Notes: The recent completion of the Escherichia coli genome sequence (Blattner et al., 1997) has permitted an analysis of the complement of genomically encoded ATP-binding cassette (ABC) proteins. A total of 79 ABC proteins makes this the largest paralogous family of proteins in E. coli. These 79 proteins include 97 ABC domains (as some proteins include more than one ABC domain) and are components of 69 independent functional systems (as many systems involve more than one ABC domain). The ABC domains are often, but not exclusively, the energy-generating domains of multicomponent membrane-bound transporters. Thus, 57 of the 69 systems are ABC transporters, of which 44 are periplasmic-binding protein-dependent uptake systems and 13 are presumed exporters. The genes encoding these ABC transporters occupy almost 5% of the genome. Of the 12 systems that are not obviously transport related, the function of only one, the excision repair protein UvrA, is known. A phylogenetic analysis suggests that the majority of ABC proteins can be assigned to 10 subfamilies. Together with statistical and, importantly, biological evidence, this analysis provides insight into the evolution and function of the ABC proteins.

Notes: Efficient acquisition of genes that encode a restriction and modification (R–M) system with specificities different from any already present in the recipient bacterium requires the sequential production of the new modification enzyme followed by the restriction activity in order that the chromosome of the recipient bacterium is protected against attack by the restriction endonuclease. We show that ClpX and ClpP, the components of ClpXP protease, are necessary for the efficient transmission of the genes encoding EcoKI and EcoAI, representatives of two families of type I R–M systems, thus implicating ClpXP in the modulation of restriction activity. Loss of ClpX imposed a bigger barrier than loss of ClpP, consistent with a dual role for ClpX, possibly as a chaperone and as a component of the ClpXP protease. Transmission of genes specifying EcoKI was more dependent on ClpX and ClpP than transmission of the genes for EcoAI. Sensitivity to absence of the protease was also influenced by the mode of gene transfer; conjugative transfer and transformation were more dependent on ClpXP than transduction. In the absence of either ClpX or ClpP transfer of the EcoKI genes by P1-mediated transduction was impaired, transfer of the EcoAI genes was not.

Notes: The eubacterial enhancer-binding proteins activate transcription by binding to distant sites and, simultaneously, contacting the RNA polymerase σ54 promoter complex (Eσ54). The positive control function is located at the central domain of these proteins, but it is not know which specific region has the determinants for the interaction with Eσ54. Here, we present genetic evidence that a small region of hydrophobic amino acids, previously denominated C3, at the central domain of Bradyrhizobium japonicum NifA is involved in positive control. We obtained 26 missense mutants along this conserved region. Among these, only strains expressing the NifAF307→Y and NifAA310→S mutant proteins retained some of the transcriptional activity (〈 20%), whereas those carrying NifAE298→D and NifAT308→S had very low but detectable activity (〈 1.0%). The rest of the NifA mutants did not induce any measurable transcriptional activity. When expressed in the presence of wild-type NifA, the great majority of the mutants displayed a dominant phenotype, suggesting that their oligomerization determinants were not altered. In vivo dimethyl-sulphate footprinting experiments for a subset of the NifA mutants showed that they were still able to bind specifically to DNA. Analysis of intragenic supressors highlight the functional role of a hydroxyl group at position 308 to activate transcription.