ALBERT

Beschreibung: Many of the difficulties of staining plastic embedded tissues for light and electron microscopy derive from physical exclusion of hydrophilic staining reagents by hydrophobic embedding media. Structures which stain most intensely with hydrophilic reagents usually contain less hydrophobic plastic than do non-staining structures. Such incomplete infiltration is apparently caused by exclusion of viscous, hydrophobic monomers by physically dense and/or well hydrated tissue elements. In keeping with this, generalized staining of tissues embedded in hydrophobic media does occur when hydrophobic reagents are used. Staining of plastic-free structures with single hydrophilic reagents or with sequences of such reagents, is, however, largely rate-controlled. The surprising similarity of hydrophilic and hydrophobic plastic embedding media is discussed. Limits of this simple model are explored, with a consideration of the roles of fixative and of monomer-tissue reactions

Beschreibung: Ulva ohnoi Hiraoka et Shimada sp. nov. (Ulvales, Ulvophyceae) is described from southern and western Japan and is characterized by the following combination of features: (i) the large, fragile, easily torn thalli, which are 30–55 μm thick in the upper and middle regions and often have microscopic marginal teeth; (ii) the production of zoids in the upper marginal region; (iii) a regular alternation of dioecious gametophytes and a sporophyte; (iv) the production of free-floating thalli from torn-off attached thalli, which reproduce vegetatively by fragmentation and form green tides in summer to autumn; (v) disorderly arranged cells that are polygonal or quadrangular in the upper and middle regions; and (vi) the chloroplast covering the outer face of cell, with 1–3 pyrenoids. Ulva ohnoi differs from U. armohcana Dion et al., U. fasciata Delile, U. reticulata Forsskal, U. scandinavica Eliding and U. spiulosaOkamura et Segawa, which all possess microscopic marginal serrations, in thallus shape, cell shape or life history pattern. It is also distinguished from morphologically similar species by sequences of the nuclear encoded internal transcribed spacers and the 5.8S ribosomal RNA gene and the plastid encoded large subunit of ribulose-l,5-bisphosphate carboxylase/oxgenase gene. Furthermore, crossing tests demonstrate that there is a reproductive boundary between U. ohnoi and the most closely related species, U. fasciata and U. reticulata.

Beschreibung: Indices of β-diversity are of two major types, (1) those that measure among-plot variability in species composition independently of the position of individual plots on spatial or environmental gradients, and (2) those that measure the extent of change in species composition along predefined gradients, i.e. species turnover. Failure to recognize this distinction can lead to the inappropriate use of some β-diversity indices to measure species turnover. Several commonly-used indices of β-diversity are based on Whittaker's βW (βW = γ/α, where γ is the number of species in an entire study area and α is the number of species per plot within the study area). It is demonstrated that these indices do not take into account the distribution of species on spatial or environmental gradients, and should therefore not be used to measure species turnover. The terms ‘β-diversity’ and ‘species turnover’ should not be used interchangeably. Species turnover can be measured using matrices of compositional similarity and physical or environmental distances among pairs of study plots. The use of indices of β-diversity and similarity-distance curves is demonstrated using simulated data sets.

Beschreibung: Measurements of the gas vesicle space in steady‐state light or phosphate‐limited cultures of Aphanizomenon flos‐aquae Ralfs, strain 7905 showed that gas vesicle content decreased as energy‐limited growth rate increased hut was the same at several phosphate‐limited growth rates. Upon a decrease in growth irradiance, gas vesicle content did increase in phosphate‐limited cultures, hut the cultures remained nonbuoyant as long as P was limiting. Buoyant, energy‐limited cultures lost their buoyancy in less than 2 h when exposed to higher irradiances. The primary mechanism for buoyancy loss was the accumulation of polysaccharide as ballast. Collapse of gas vesicles by turgor pressure played a minor role in the loss of buoyancy. When cultures were exposed to higher irradiances, cells continued to synthesize gas vesicles at the same rate as before the shift for at least 1 generation time. The amount of ballast required to make individual filaments in the population sink varied 4‐fold. This variation appears to be due to differences in gas vesicle content among individual filaments.

Beschreibung: The dissection of Heterorotula sponges collected in an area of geothermal activity at 126–145 m depth on the floor of Lake Taupo (de Rondeet al., 2002) revealed a dense population of associated Enchytraeidae. They represent three species of Marionina, two of which known but exotic (the Palaearctic M. ripariaBretscher, 1899 and the Chinese M. seminudaXie and Rota, 2001), and one new to science, M. spongicola sp. n. This is the first report of an ecological association between enchytraeids and poriferans in the lake profundal zone. The possible nature of such relationship (casual contact for feeding or dwelling for food and shelter) is discussed.

Beschreibung: Porewater fluxes into or out of the sediments in aquatic systems are frequently estimated using Fick's First Law. This assumes that diffusive processes control the transport of nutrients. As a corollary, advection, bioturbation and chemical processes are assumed not to be significant. Through a series of sediment core incubations, this paper seeks to quantify the uncertainties involved in such assumptions. Duplicate sediment cores were collected from 28 sites along the Swan–Canning Estuary, returned to the laboratory and incubated under oxic or anoxic conditions. Porewater nutrient concentrations, sediment porosity and initial nutrient concentrations in the overlying water were measured. These parameters were used to estimate the expected nutrient fluxes via Fick's First Law. The estimated fluxes were then compared with measured fluxes of nutrients out of the sediments over the incubation period. Severe bioturbation occurred in several of the anoxic treatments, resulting in large releases of nutrients into the overlying water. Aside from these bioturbated cores, phosphate and ammonium fluxes under anoxic conditions are well predicted by Fick's First Law. Nitrate fluxes are predicted well under oxic conditions. For coarse sediments (D10 averaging 0·3 mm) and under redox conditions favourable for nutrient release, Fick's First Law predicted close to 100% of the observed fluxes. For finer grain sediments (D10 〈 0·01 mm), Fick's First Law overestimated the observed flux by up to 40%. Under unfavourable oxygen conditions, chemical retardation processes are likely to dominate fluxes, and the error associated with using Fick's First Law is increased. These results confirm the usefulness of using Fick's First Law for a baseline estimate of nutrient fluxes under favourable redox conditions. Much greater care must be taken when using Fick's First Law to estimate nutrient fluxes under unfavourable redox conditions, or under conditions when bioturbation is likely to be severe.

Beschreibung: While consumer species diversity is known to influence the capture of limited resources, little is known about how prey diversity impacts the transfer of energy and matter among trophic levels. Here, we perform a meta-analysis of experiments that have examined the impact of grazers on the biomass of periphytic algae to test the hypothesis that the magnitude of consumer (grazer) effects on prey (algae) depends on the species diversity of the prey assemblage. The analysis reveals that consumer effects tend to decrease as the diversity of a prey assemblage increases. This trend is robust for several different, yet complementary indices of grazer effect size and algal diversity. The trend also remains significant after statistically controlling for a variety of factors that can covary with prey diversity among studies. We discuss several possible mechanisms for the documented pattern, such as diversity enhancing the probability of inedibility and of positive interactions.

Beschreibung: Agar oligosaccharides in the neoagarobiose series were prepared by partial enzyme hydrolysis, separated on Biogel P2 and P4, and analyzed by high-performance anion exchange chromatography with pulsed amperometric detection, yielding neoagarosaccharide fractions with a disaccharide repetition degree ranging from 1 (neoagarobiose) to more than 8 (neoagarohexadecaose). These fractions were analyzed for their biological activity toward the marine red alga Gracilaria conferta (Schousboe ex Montagne) J. et G. Feldmann in terms of increase of oxygen consumption, release of hydrogen peroxide, elimination of epiphytic bacteria, and induction of thallus tip bleaching. The structure–activity and dose–response relationships of neoagarosaccharides were very similar in the respiratory and oxidative burst responses and in their bactericidal properties, with neoagarosaccharides consisting of 6 to 8 disaccharide repeating units being the most active. All these responses were competitively inhibited by the reduced form of neoagarohexaose, neoagarohexaitol. In contrast, the tip-bleaching response was light dependent, required much higher concentrations of neoagarosaccharides, and was not inhibited by neoagarohexaitol, suggesting that it is an unspecific oxidative stress reaction. Putative structural effects on the recognition of endogenous agar-oligosaccharide elicitors by G. conferta are discussed.

Beschreibung: Sponges of the Aplysinidae family contain large amounts of bacteria that are embedded within the sponge tissue matrix. In order to determine the stability and specificity of the Aplysina–microbe association, sponges were maintained in recirculating seawater aquariums for 11 days. One aquarium was left untreated, a second one contained 0.45 μm filtered seawater (starvation conditions) and the third one contained 0.45 μm filtered seawater plus antibiotics (antibiotics exposure). Changes in the microbial community were monitored using group-specific, 16S rRNA targeted oligonucleotide probes, by denaturing gradient gel electrophoresis and by electron microscopic observations. Furthermore, the changes in the natural product profile were monitored using high-performance liquid chromatography. The measured parameters showed that a large fraction of the sponge-associated microbial community could not be cleared under the given experimental conditions. Based on these cumulative results we postulate that a large fraction of sponge-associated bacteria resides permanently in the Aplysina aerophoba mesohyl pointing to a highly integrated interaction between the host sponge and associated microorganisms.

Beschreibung: The aim of this study was to isolate bacteria with antimicrobial activities from the marine sponges Aplysina aerophoba and Aplysina cavernicola. The obtained 27 isolates could be subdivided into eight phylogenetically different clusters based on comparative sequence analysis of their 16S rDNA genes. The sponge isolates were affiliated with the low (Bacillus) and high G+C Gram-positive bacteria (Arthobacter, Micrococcus), as well as the α-Proteobacteria (unknown isolate) and γ-Proteobacteria (Vibrio, Pseudoalteromonas). One novel Bacillus species was identified and two species were closely related to previously uncharacterized strains. Isolates with antimicrobial activity were numerically most abundant in the genera Pseudoalteromonas and the α-Proteobacteria. The sponge isolates show antimicrobial activities against Gram-positive and Gram-negative reference strains but not against the fungus Candida albicans. A general pattern was observed in that Gram-positive bacteria inhibited Gram-positive strains while Gram-negative bacteria inhibited Gram-negative isolates. Antimicrobial activities were also found against clinical isolates, i.e. multi-resistant Staphylococcus aureus and Staphylococcus epidermidis strains isolated from hospital patients. The high recovery of strains with antimicrobial activity suggests that marine sponges represent an ecological niche which harbors a hitherto largely uncharacterized microbial diversity and, concomitantly, a yet untapped metabolic potential.

Beschreibung: A 550-km-long transect across the Ninetyeast Ridge, a major Indian ocean hotspot trail, provided seismic refraction and wide-angle reflection data recorded on 60 ocean bottom instruments. About 24 000 crustal and 15 000 upper mantle arrivals have been picked and used to derive an image of the hotspot track. Two approaches have been chosen: (i) a first-arrival tomographic inversion yielding crustal properties; and (ii) forward modelling of mantle phases revealing the structure at the crust–mantle boundary region and of the uppermost mantle. Away from the volcanic edifice, seismic recordings show the typical phases from oceanic crust, that is, two crustal refraction branches (Pg), a wide-angle reflection from the crust–mantle boundary (PmP) and a wave group turning within the upper mantle (Pn). Approaching the edifice, three additional phases have been detected. We interpret these arrivals as a wide-angle reflection from the base of material trapped under the pre-hotspot crust (Pm2P) and as a wide-angle reflection (PnP) and its associated refraction branch (PN) from a layered upper mantle. The resulting models indicate normal oceanic crust to the west and east of the edifice. Crustal thickness averages 6.5–7 km. Wide-angle reflections from both the pre-hotspot and the post-hotspot crust–mantle boundary suggest that the crust under the ridge has been bent downwards by loading the lithosphere, and hotspot volcanism has underplated the pre-existing crust with material characterized by seismic velocities intermediate between those of mafic lower crustal and ultramafic upper mantle rocks (7.5–7.6 km s−1). In total, the crust is up to ≈ 24 km thick. The ratio between the volume of subcrustal plutonism forming the underplate and extrusive and intrusive volcanism forming the edifice is about 0.7. An important observation is that underplating continued to the east under the Wharton Basin. During the shield-building phase, however, Ninetyeast Ridge was located adjacent to the Broken Ridge and was subsequently pulled apart along a transform fault boundary. Therefore, underplating eastwards of the fracture zone separating the edifice from the Wharton Basin suggests that prolonged crustal growth by subcrustal plutonism occurred over millions of years after the major shield-building stage. This fact, however, requires mantle flow along the fossil hotspot trail. The occurrence of PnP and PN arrivals is probably associated with a layered and anisotropic upper mantle due to the preferential alignment of olivine crystals and may have formed by rising plume material which spread away under the base of the lithosphere.

Beschreibung: The behaviour of Magellanic Penguins Spheniscus magellanicus commuting between their foraging areas and breeding areas in San Julian Bay, Argentina was studied to examine whether tidal rip currents affected travelling patterns. Although there was no apparent relationship between departure and arrival patterns and the state of the tidal cycle, birds travelling against the current dived for longer periods and had shorter rests on the surface than birds travelling with the current. In addition, birds swimming against the current hugged the banks of tidal rivers much more closely than did birds swimming with the current, thus reducing the magnitude of the current against which they had to swim. In cases of extremely high current speeds, birds travelling upstream walked. Models regarding the energetics of movement indicate that the strategies adopted by Magellanic Penguins can result in substantial energy savings.

Beschreibung: The Alhambra (14th century AD) in Granada (southeast Spain) is built at the summit of a Pliocene to Lower Pleistocene conglomeratic formation. Tens of small-scale normal faults crop out along the northern hillslope of the Alhambra, which have a N130–N150°E strike, dipping 65–75° mostly to the southwest. These are closely spaced faults (approximately 5–30 m) with centimetre to several metre displacements. Several topographic steps in this area coincide with hectometre- to kilometre-scale faults with the same kinematics as the small-scale ones. Some of these faults appear to be active and related to the present seismicity detected in this region, and associated with the cracks and other damage observed in the Alhambra. Several focal mechanisms calculated in this study are in accordance with the dominant NW–SE orientated normal faults. We interpret that the topographic steps of these faults are a consequence of repeated earthquakes during the past 800 ka. The last large earthquake of approximately 5.1 magnitude in this area occurred in 1431, destroying the Alixares Palace, the Arabian fence and part of the Alhambra wall. We consider the seismic risk associated with these faults to be moderate, as the displacement is partitioned into several hectometre- to kilometre-scale faults.

Beschreibung: Notations for Cd stable isotope compositions and the use of reference materials are discussed. It is proposed that Cd stable isotope data should be reported as variations of the 114Cd/110Cd ratio/ using either the δ114/110Cd or ε114/110Cd notations. Future publications should report results for BAM-1012 Cd, the only currently available international Cd isotope reference material. It is also recommended that “Münster Cd” and a range of specified geological reference materials are used as additional reference materials. The final choice of a primary “zero-delta” reference standard remains the most important outstanding question.

Beschreibung: The region of north Iceland is highly sensitive climatically owing to its location with respect to atmospheric and oceanographic fronts. In this study we present total carbonate and δ18O records of benthic and planktic Foraminifera from nine sediment cores from the North Iceland Shelf. The results of this work indicate that the deglaciation of the Vestfirdir Peninsula was completed by 10 200 cal. yr BP. The 8200 cal. yr BP cold event is present only as a minor isotopic event, and seems not to have had much of a cooling effect on the bottom waters of the northwest Iceland shelf. The Holocene maximum warmth, attributed to a stronger North Icelandic Irminger Current, occurred between ca. 7800 and 6200 cal. yr BP. Over the past 4500 cal. yr BP a general cooling trend has occurred on the North Iceland Shelf, and superimposed on this overall cooling trend are a number of oscillations between periods when relatively warmer and cooler waters occupied the shelf. Relatively cooler waters were present at 4200–4000 cal. yr BP, 3200–2900 cal. yr BP, 2500–2350 cal. yr BP and 600–200 cal. yr BP, whereas relatively warmer waters were present on the shelf at 3750–3450 cal. yr BP, 2800–2600 cal. yr BP and 1700–1000 cal. yr BP.

Beschreibung: 1. Density gradients of cladocerans and copepods were generated in an enclosure experiment to compare the impact on the plankton of a filter feeder (Daphnia hyalina × galeata) with that of more selective feeders (calanoid and cyclopoid copepods). The experiment was conducted in situ over 25 days during spring in a mesotrophic lake, Schöhsee, Germany. 2. The plankton community was monitored regularly. Daphniids were able to graze on the phytoplankton present, which mainly consisted of small (〈1000 μm3) species, whereas copepods did not show any impact on algae. 3. At the end of the experiment, Daphnia and remaining cyclopoid copepods were harvested and sorted manually, prior to analyses for stable isotopes of carbon and nitrogen. Daphniids from mesocosms stocked purely with differing densities of Daphnia showed little variability in stable isotope values, whereas those that thrived in enclosure bags together with copepods exhibited lower δ13C values. 4. The change in Daphniaδ13C indicates a change of food sources, modified by the presence of the copepods: the higher the mean abundance of copepods in the enclosures, the more 13C-depleted the daphniids. Increasing abundance of high nucleic acid (HNA) bacteria in the copepod bags may account for the trend in Daphniaδ13C via increased grazing on the bacteria themselves, or via grazing on phytoplankton utilising isotopically light CO2 from respiratory release. 5. Cyclopoid copepod stable isotope signatures were related to Daphnia and copepod abundances in copepod bags, suggesting that cyclopoids preyed on the available zooplankton.

Beschreibung: In order to clarify mechanisms influencing the reproductive success of Baltic cod (Gadus morhua L.), a modelling exercise was performed to examine the effects of the wind-driven circulation on the transport of early life stages between the western and eastern Baltic. Because the different stocks spawn in different areas and environments at different times of the year, the occurrence of variable age/length distributions of juveniles within the different potential nursery areas can be explained by the circulation pattern. A three-dimensional circulation model of the Baltic was utilized to investigate the temporal evolution of egg and larval distributions of the western Baltic cod stock, which spawns preferentially in the Danish Straits, in Kiel Bay as well as in Mecklenburg Bay. For different scenarios (1988 and 1993), within- and between-year variability of egg and larval transport showed large differences, primarily due to variations in wind forcing. In 1988, relatively low and variable wind forcing prevailed, whereas, due to sustained strong, mainly westerly, winds, in January 1993, the recent major Baltic inflow to the Baltic Sea occurred. Differences in contributions of early life stages from the western to the eastern cod stocks, depending on the physical forcing conditions, suggest that this process can be controlled by variations of atmospheric forcing conditions. The potential for early life stages from the western Baltic cod stock to drift into the Arkona Basin and the Bornholm Basin, and to contribute there to the juvenile population, has been recognized as being mainly due to strong westerly winds. During cold winters, retention of eggs, larvae and juveniles within their original spawning grounds may predominate. Transport of cod early life stages from the Øresund, as well as from the Great Belt, can occur only during periods of strong westerly winds, but significant eastwards orientated drift from Kiel Bay and Mecklenburg Bay was also evident during periods of minor westerly wind influence.

Beschreibung: Over the last two decades numerous studies have investigated the structure of the west Iberia continental margin, a non-volcanic margin characterized by a broad continent–ocean transition (COT). However, the nature and structure of the crust of the segment of the margin off SW Iberia is still poorly understood, because of sparse geophysical and geological data coverage. Here we present a 275-km-long multichannel seismic reflection (MCS) profile, line AR01, acquired in E–W direction across the Horseshoe Abyssal Plain, to partially fill the gap of information along the SW Iberia margin. Line AR01 runs across the inferred plate boundary between the Iberian and the African plates during the opening of the Central Atlantic ocean. The boundary separates crust formed during or soon after continental rifting of the SW Iberian margin from normal seafloor spreading oceanic crust of the Central Atlantic ocean. Line AR01 has been processed and pre-stack depth migrated to show the tectonic structure of the crust across the palaeo plate boundary. This boundary is characterized by a 30–40-km-wide zone of large basements highs related to landward-dipping reflections, which penetrate to depths of 13–15 km, and it marks a change in the character of the basement structure and relief from east to west. In this study, we have used pre-stack depth migrated images, the velocity model of line AR01 and magnetic data available in the area to show that the change in basement structure occurs across the fossil plate boundary, separating African oceanic crust of the M series (M21–M16) to the west from the transitional crust of the Iberian margin to the east.

Beschreibung: Active seismic investigations along the Pacific margin off Peru were carried out using ocean bottom hydrophones and seismometers. The structure and the P-wave velocities of the obliquely subducting oceanic Nazca Plate and overriding South American Plate from 8°S to 15°S were determined by modelling the wide-angle seismic data combined with the analysis of reflection seismic data. Three detailed cross-sections of the subduction zone of the Peruvian margin and one strike-line across the Lima Basin are presented here. The oceanic crust of the Nazca Plate, with a thin pelagic sediment cover, ranging from 0–200 m, has an average thickness of 6.4 km. At 8°S it thins to 4 km in the area of Trujillo Trough, a graben-like structure. Across the margin, the plate boundary can be traced to 25 km depth. As inferred from the velocity models, a frontal prism exists adjacent to the trench axis and is associated with the steep lower slope. Terrigeneous sediments are proposed to be transported downslope due to gravitational forces and comprise the frontal prism, characterized by low seismic P-wave velocities. The lower slope material accretes against a backstop structure, which is defined by higher seismic P-wave velocities, 3.5–6.0 km s−1. The large variations in surface slope along one transect may reflect basal removal of upper plate material, thus steepening the slope surface. Subduction processes along the Peruvian margin are dominated by tectonic erosion indicated by the large margin taper, the shape and bending of the subducting slab, laterally varying slope angles and the material properties of the overriding continental plate. The erosional mechanisms, frontal and basal erosion, result in the steepening of the slope and consequent slope failure.

Beschreibung: A recent meta-analysis indicates that trophic cascades (indirect effects of predators on plants via herbivores) are weak in marine plankton in striking contrast to freshwater plankton (Shurin et al. 2002, Ecol. Lett., 5, 785–791). Here we show that in a marine plankton community consisting of jellyfish, calanoid copepods and algae, jellyfish predation consistently reduced copepods but produced two distinct, opposite responses of algal biomass. Calanoid copepods act as a switch between alternative trophic cascades along food chains of different length and with counteracting effects on algal biomass. Copepods reduced large algae but simultaneously promoted small algae by feeding on ciliates. The net effect of jellyfish on total algal biomass was positive when large algae were initially abundant in the phytoplankton, negative when small algae were dominant, but zero when experiments were analysed in combination. In contrast to marine systems, major pathways of energy flow in Daphnia-dominated freshwater systems are of similar chain length. Thus, differences in the length of alternative, parallel food chains may explain the apparent discrepancy in trophic cascade strength between freshwater and marine planktonic systems.

Beschreibung: In most groups of organisms, the species richness decreases from the tropics to the poles. The mechanisms causing this latitudinal diversity gradient are still controversial. We present data from a comprehensive weighted meta-analysis on the strength of the latitudinal gradient in relation to body size. We sampled literature data on the correlation between species richness and latitude for a variety of organisms, ranging from trees to protozoa. In addition, own data on the presence of large-scale diversity patterns for diatoms were included, both for local and regional species richness. The strength of the latitudinal gradient was positively correlated to the size of the organisms. Strongest decreases of species richness to the poles was found for large organisms like trees and vertebrates, whereas meiofauna, protozoa and diatoms showed weak or no correlations between species richness and latitude. These results imply that latitudinal gradients are shaped by non-equilibrium (regional) processes and are persistent under conditions of dispersal limitation.

Beschreibung: Nonmammalian tooth-bearing vertebrates usually replace their teeth throughout life. Much about how a replacement pattern is generated has been learned from zebrafish. However, to understand general mechanisms of tooth replacement, advantage can be taken from studying other, “nonmodel” species. We have mapped the patterns of tooth replacement in widely divergent aquatic osteichthyans using 2D charts, in which one axis is time, the other linear spacing along the tooth row. New teeth that are generated simultaneously are considered part of the same odontogenic wave. Using this approach, it appears that a similar, general pattern underlies very distinctive dentitions in distantly related species. A simple shift in spacing of odontogenic waves, or in distance between subsequent tooth positions along a row (or both), can produce dramatically different dentitions between life stages within a species, or between closely related species. Examples will be presented from salmonids, cyprinids, and cichlids. Our observations suggest that lines linking subsequent positions may have more biological significance than replacement waves (usually linking alternate positions), often used to explain the generation of patterns. The presence of a general pattern raises questions about common control mechanisms. There is now increasing evidence, at least for the zebrafish, to support a role for stem cells in continuous tooth renewal and control of replacement patterns.

Beschreibung: We present depth images, from portions of profiles that are close to flow-lines, of Cretaceous oceanic crust in the eastern Central Atlantic. Compared with post-stack time migrations, the images illustrate the improvement resulting from the application of pre-stack depth migration. The images document the scale and geometry of normal faulting in oceanic crust formed over 25 Myr at a half-spreading rate of less than 10 mm yr−1, and the variation in extensional style with position within the spreading segment. Away from major fault zones (FZs), most faults are subplanar, dip more than 35°, are associated with moderate basement relief (0.2–1 km relief) and may penetrate to deep crustal levels. These faults could be related to the lifting of the lithosphere out of the median valley to the flanking mountains. Also observed away from FZs are gently dipping to subhorizontal reflections in the upper crust, which resemble detachment faults. In contrast, the inside corner crust is more rugged, with basement highs rising up to 2 km above the intervening basins. This larger-scale topography is associated with a different style of faulting: the depth images reveal gently dipping (〈35°) faults that are rooted in the deep crust and that project to the ridgeward flank of the dome-shaped large basement highs (1–2 km vertical relief). The faults seem to continue as the ridge-facing flank of these highs and some may extend over the crest of the high to breakaways beyond. In this case, the domal highs that form the exhumed footwall to the faults can be described as oceanic core complexes. These controlling faults are up to 20 km long and have a heave of ∼10 km, sufficient to have accommodated up to 50 per cent extension and to have exhumed deep crustal and perhaps even mantle rocks. We suggest that similar faults can explain the structure and lithologies found at megamullion structures (oceanic core complexes) at inside corners near the present-day spreading ridge.

Beschreibung: Ambient UV radiation has substantially increased during the last decades, but its impact on marine benthic communities is hardly known. The aim of this study was to globally compare and quantify how shallow hard-bottom communities are affected by UV during early succession. Identical field experiments in 10 different coastal regions of both hemispheres produced a consistent but unexpected pattern: (i) UV radiation affected species diversity and community biomass in a very similar manner, (ii) diversity and biomass were reduced to a larger extent by UVA than UVB radiation, (iii) ambient UV levels did not affect the composition of the communities, and (iv) any UV effects disappeared during species succession after 2–3 months. Thus, current levels of UV radiation seem to have small, predictable, and transient effects on shallow marine hard-bottom communities.

Beschreibung: A population dynamics analysis for planktonic diatoms is presented that allows estimates of the net rate of increase (k), the death rate (δ), the sedimentation rate (σ) and, in absence of grazing, the growth rate (μ). It requires counts of live and dead cells suspended in the euphotic part of the water column and accumulated in sedimentation traps. The application of the model is demonstrated for the three dominant summe diatom species in Lake Constance. Asterionella formosa Hass, Fragilaria crotonensis Kitton and Stephanodiscus binderanus Krieger. Only during the first two weeks of the summer bloom of diatoms the loss rates were unimportant in comparison to the growth rates. Thereafter diatom population dynamics was strongly influenced by sedimentation and mortality, which sometimes led to a decrease in population density even when cell division continued at high rates. There were two periods of extraordinarily high death rates, which were associated in the case of A. formosa with silicon depletion and in the case of F crotensis with fungal parasitism.

Beschreibung: The influence of periodic salinity changes was investigated for 42 days under semicontinuous culture conditions with phosphorus limitation using phytoplankton assemblages from Lake Waihola, a tidally influenced shallow lake. To simulate tidal effects on the phytoplankton community, salinity in the cultures was increased in pulses at different intervals (3.5, 7, and 14 days), and these cultures were compared with those that experienced constant freshwater conditions. Salinity pulses significantly affected competition and succession with a major loss in diversity during the first days of the experiment due to the initial pulse that caused a transition from freshwater to brackish conditions in the cultures. After this initial phase, diversity index (H') and species number (Scorr) decreased less rapidly. The loss in H' and Scorr over time was highest under constant freshwater conditions and lowest in the treatment with an interval of 3.5 days between salinity pulses. At the end of the experiment, the combination of initial loss in H' and Scorr and the time course of H' and Scorr resulted in a U‐shaped relation between the interval length of salinity pulses and both H' and Scorrtemp1.txttemp1.txt. Our results indicate that salinity pulses at intervals of a few days tend to promote phytoplankton diversity. If saline intrusions in coastal freshwater systems occur only at spring tides, this will lead to decreases in diversity and species richness.

Beschreibung: The isolation and structure elucidation of two new oleanane-type triterpene glycosides, 29-(β-D-glucopyranosyloxy)-2α,3β,23-trihydroxyolean-12-en-28-oic acid (=(2α,3β,4α,29α)-29-(β-D-glucopyranosyloxy)-2,3,23-trihydroxyolean-12-en-28-oic acid; 1) and its C(20)-epimer, 30-(β-D-glucopyranosyloxy)-2α,3β,23-trihydroxyolean-12-en-28-oic acid (=(2α,3β,4α,29β)-29-β-D-glucopyranosyloxy)-2,3,23-trihydroxyolean-12-en-28-oic acid; 2), and a novel nortriterpene glycoside, (17S)-2α,18β,23-trihydroxy-3,19-dioxo-19(18[RIGHTWARDS ARROW]17)- abeo-28-norolean-12-en-25-oic acid β-D-glucopyranosyl ester (=(1R,2S,4aS,4bR,6aR,7R,9R,10aS,10bS)-3,4,4a,4b,5,6,6a,7,8,9,10,10a,10b,11-tetradecahydro-1-hydroxy-7-(hydroxymethyl)-3′,4′,4a,4b,7-pentamethyl-2′,8- dioxospiro[chrysene-2(1H),1′-cyclopentane]-10a-carboxylic acid β-D-glucopyranosyl ester; 3) from Phlomis viscosa (Lamiaceae) are reported. The structures of the compounds were asigned by means of spectroscopic (IR, 1D- and 2D-NMR, and LC-ESI-MS) and chemical (acetylation) methods.

Beschreibung: Broadband receiver functions developed from teleseismic P waveforms recorded on the midperiod passband of Regional Seismic Test Network station RSCP are inverted for vertical velocity structure beneath the Cumberland Plateau, Tennessee. The detailed broadband receiver functions are obtained by stacking source‐equalized horizontal components of teleseismic P waveforms. The resulting receiver functions are most sensitive to the shear velocity structure near the station. A time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin, flat‐lying, homogeneous layers. Lateral changes in structure are identified by examining azimuthal variations in the vertical structure. The results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the East Continent Gravity High located northeast of RSCP. The results from events arriving from the northeast show a high‐velocity midcrustal layer not present in results from the southeast azimuth. This velocity structure can be shown to support the idea that this feature is part of a Keweenawan rift system. Another interesting feature of the derived velocity models is the indication that the crust‐mantle boundary beneath the Cumberland Plateau is a thick, probably laminated transition zone between the depths of 40 and 55 km, a result consistent with interpretations of early refraction work in the area.

Beschreibung: The Patagonian longfin squid Loligo gahi undertakes horizontal ontogenetic migrations on the Falkland shelf: juveniles move from spawning grounds located in shallow, inshore waters (20–50 m depths) to feeding grounds near the shelf edge (200–350 m depths). Immature squid feed and grow in these offshore feeding grounds and, upon maturation, migrate back to inshore waters to spawn. The possible influence of environmental factors on L. gahi migrations was investigated using data from oceanographic transects, crossing the region of known L. gahi occurrence. They were made from the inshore waters of East Falkland eastwards to depths of 1250 m on a monthly basis from 1999 to 2001. Four main water types were found in the region: Shelf, Sub-Antarctic Superficial and Antarctic Intermediate water masses, and Transient Zone waters. The inshore spawning grounds occur in the Shelf Water mass, whereas the feeding squid (medium-sized immature and maturing individuals) were associated with the Transient Zone. The 5.5°C isotherm appeared to mark the limit of squid distribution into deeper waters in all seasons. Seasonal changes in water mass characteristics and location were found to be important for seasonal changes in L. gahi migrations on the Falkland shelf.

Beschreibung: The reproductive system is described from 15 giant squid Architeuthis sp., collected between 1972 and 2002 in South African waters. Distinctive features of the male reproductive system are the long muscular terminal organ, with elaboration of the anterior end, and modification of the tips of the ventral arms, probably hectocotilization. The spermatophoric organ has a long finishing gland that extends from the base of the gill. The terminal organ is differentiated internally into three distinct parts, involved in the guidance, storage, protection, expulsion and possibly the coating of spermatophores. Length of spermatophores in the terminal organ varied considerably. Several stages of spermatophores were found, from tentative to false to fully formed spermatophores, within a single animal. Distinctive features of the female reproductive system are a mesentery surrounding the main blood vessels of the ovary and attaching the ovary to the dorsal gladius chamber, multiple branching (at least three times) of the genital aorta that supplies the developing oocytes, high potential fecundity (3.5–6.2 ± 106 oocytes), small eggs and short oviducts that suggest intermittent (extended) spawning. Large concentrations and single spermatangia were found in various places in females, indicating non-specific deposition. The transfer of spermatophores is probably rapid, perhaps because of considerable sexual size dimorphism (at maturity, males are much smaller than females). Implants in males are probably self-induced since the majority were found within reach of the terminal organ opening (primarily on the ventral arms in males).

Beschreibung: Oxidative stability of lipids from squid tissues was compared with those of other marine lipids. On the basis of peroxide formation, total lipids (TL) from squid viscera or squid muscle with skin were most oxidatively stable, followed by squid eye TL, trout egg TL, bonito oil, and tuna orbital TL, respectively. This tendency in oxidative stabilities was also confirmed by the decrease in unoxidized polyunsaturated fatty acids during oxidation. Analyses of tocopherol contents and lipid compositions suggested that the higher oxidative stabilities of three kinds of squid tissue TL and trout egg TL compared to those of bonito oil and tuna orbital TL would be mainly because of the presence of phospholipids (PL) in squid tissue lipids and trout egg TL. However, the oxidative stability of lipids containing PL did not always decrease with increasing PL contents and stability was strongly influenced by PL composition. As squid viscera contained more than 25% of TL and these lipids were oxidatively stable, squid viscera may be used as a good resource of functional lipids rich in eicosapentaenoic acid and docosahexaenoic acid.

Beschreibung: In this study, we consider the influence of mesoscale oceanographic processes around the Falkland Islands (Islas Malvinas) in the South-west Atlantic, during the period in which the commercial squid fishery for Illex argentinus operates. Spatially referenced fishery data and satellite-derived advanced very high resolution radiometry (AVHRR) sea surface temperature (SST) data were examined using geographic information system (GIS) techniques. The distribution and relative abundance of I. argentinus in the Falkland Islands fishery was examined for the period 1989–96. Three consistent areas of high abundance were observed to the north-east (shelf-break region) and north-west (shelf region) of the islands, and close to the northern coast of East Falkland. Areas of high sea surface temperature gradients (thermal gradients) extracted from remotely sensed satellite images were used as an indicator of mesoscale oceanographic activity and compared with the location of the fishery. I. argentinus were found to be associated with areas of thermal gradients, commonly seen at the interface of Falkland Current and Patagonian shelf waters. The techniques used in this analysis allow the overlay and analysis of physical oceanographic and fishery data with potential applications in fisheries management and operational fisheries oceanography.

Beschreibung: This study examined the changing status of the marine ecosystem at the island of South Georgia (Southern Ocean) using up to 27 variables measured over 22 years from three upper trophic level predators that specialize in foraging upon krill (Eupuasia superba Dana). These variables included population size, breeding performance, offspring growth rate, foraging behaviour and diet. A method was developed for reducing these multivariate time-series to a single vector, called a combined standardized index (CSI). 2 Sensitivity analyses showed that missing values had a large effect upon the accuracy of the CSI but this effect was reduced if the individual variables were highly correlated. The level of correlation and proportion of missing values within the empirical data set were within the acceptable range. Individual variables had widely varying influence upon the CSI but, in general, those with longer time-series had the greatest influence. 3 Principal components analysis showed that variables representing offspring growth tended to explain the greatest proportion of the variability in the CSI and this was followed by variables representing diet. 4 There were 3 years in which the CSI showed extreme and significantly low values. There was a significant non-linear functional response (similar to the Holling Type II functional response) between the overall CSI and krill biomass and a similar relationship existed when the CSI was calculated for each species individually. 5 Separate analysis of variables that were likely to be representative of changing population size showed the presence of a significant decline between 1977 and 1998. There was no trend in the CSI from variables representative of foraging conditions during the summer breeding season. The study has shown that the marine ecosystem at South Georgia shows acute but transient variability that is amplified in the response of upper trophic-level predators. There is less certainty that trends in populations are a consequence of shifts in the degree to which the ecosystem can support krill-feeding seals and penguins.

Beschreibung: Cephalopod reproductive strategies are reviewed in order to clarify their current, confusing status. Based on the type of ovulation, spawning pattern and growth between egg batches or spawning periods, five comprehensive and flexible cephalopod reproductive strategies are defined. Accordingly, with these three factors the following classification is proposed. (a) Spawning once (formerly semelparity) consisting of simultaneous terminal spawning, with synchronous ovulation, monocyclic spawning and absence of growth between egg batches. (b) Spawning more than once (formerly iteroparity) including: (i) polycyclic spawning with egg-laying occurring in separate batches during the spawning season and growth occurring between production of egg batches and spawning seasons; (ii) multiple spawning, with group-synchronous ovulation, monocyclic spawning and growth between egg batches; (iii) intermittent terminal spawning, with group-synchronous ovulation, monocyclic spawning and no growth between egg batches; (iv) continuous spawning, with asynchronous ovulation, monocyclic spawning and growth between egg batches. Examples of species exhibiting each of these reproductive strategies are given. The large amount of inter-species variation in several life-history traits related to reproductive events is discussed.

Beschreibung: Individual growth rates, feeding rates (%BWd−1) and food conversions for cuttlefish (S. officinalis) hatchlings and juveniles were determined during this study. A flow-through system was used. Water temperature reached 30 °C during the hottest part of the day, gradually decreasing to 25 °C during the night; salinity varied between 37 ± 3 ppt and lights were kept on for 14 h day−1. Hatchlings were placed in separate compartments with a water volume of 1.2 L. Juvenile cuttlefish (from 0.5 to 25 g) were placed in bigger baskets, with a water volume of 5.2 L. Water flow was 120 L h−1. The biggest cuttlefish used in these experiments (〉 25 g) were gathered in groups of five and placed in circular tanks (water volume of 250–300 L). Thus, results obtained in this case are means and not individual data. During the first 10, 20, 30 and 40 days, mean growth rates (of all individuals sampled by age group) decreased consistently (11.8 ± 4.1, 9.8 ± 1.8, 8.1 ± 2.2 and 7.3 ± 0.7%BW−1 respectively); in similar fashion, mean feeding rates decreased with age group (33.7 ± 13.5, 22.0 ± 7.9, 17.3 ± 3.9 and 16.7%BWd−1 respectively). Mean food conversions varied between 3.6 and 2.5 between the age groups. When grouping results by weight class, similar patterns occur, as growth and feeding rates decrease consistently as cuttlefish grow bigger. Highest mean growth and feeding rates are obtained by hatchlings (〈 0.1 g) with 12.4 ± 4.5 and 35.3 ± 15.1%BWd−1, respectively, while the lowest growth and feeding rates were recorded for the largest animals, between 15 and 25 g (3.4 ± 1.1 and 10.8 ± 4.1%BWd−1 respectively). For these weight classes, mean food conversions varied between 2.7 ± 0.9 and 3.8 ± 2.8.

Beschreibung: The convergent margin of the central Sunda Arc in Indonesia was the target of a reflection and refraction seismic survey conducted in 1998 and 1999. Along two seismic lines across the subduction complex off southern Sumatra and off Sunda Strait, coincident multichannel and wide-angle data were collected, complemented by two refraction strike-lines in the forearc basin off Sumatra. The combined analysis of the acquired data allows us to present a detailed model of the subduction zone where initiation of strain partitioning occurs due to the onset of oblique subduction. The dip of the subducted plate is well defined along both dip-lines and a lateral increase from 5° to 7° from beneath the outer high off Sumatra to Sunda Strait is supported by complementary gravity modelling. The downgoing slab is traced to a depth of more than 30km. On both reflection dip-lines, a clearly developed backstop structure underlying a trench slope break defines the landward termination of the active accretionary prism and separates it from the outer high. Active subduction accretion is supported by laterally increasing velocities between the deformation front and the active backstop structure. Seismic velocities of the outer high are moderate along both lines (〈5.8kms−1 at 20km depth), suggesting a sedimentary composition. Reduced reflectivity beneath a rugged top basement traced along the outer high of both dip-lines supports a high degree of deformation and material compaction. Several kilometres of sediment has accumulated in the forearc domain, although a distinct morphological basin is only recognized off southern Sumatra and is not developed off Sunda Strait. The bathymetric elevation of the Java shelf that is encountered in the southern Sunda Strait corresponds to increased velocities of a basement high there and is connected to extensional structures of the Sunda Strait transtensional basin. Differences observed in the morphology of the forearc domain are also reflected in the lower crustal structure. Off southern Sumatra, the velocity–depth model clearly indicates a continental-type crust underlying the forearc basin, whereas lower velocities are found beneath the Sunda Strait forearc domain. Off Sumatra, some 3-D constraint on the upper plate structure is gained from the refraction strike-lines, which in addition is supported by synthetic data modelling.

Beschreibung: Alkaline phosphatase activities of the diazotrophic marine cyanobacterium Trichodesmium were studied among natural populations in the northern Red Sea and in laboratory cultures of Trichodesmium sp. strain WH9601. Open‐water tuft‐shaped colonies of Trichodesmium showed high alkaline phosphatase activities with 2.4–11.7 μmol p‐nitrophenylphosphate (PNPP) hydrolyzed·μg chl a−1·h−1, irrespective of date or origin of the sample. Coastal populations of the Trichodesmium tuft colonies had low alkaline phosphatase activities with 0.2–0.5 μmol PNPP·μg chl a−1·h−1. An exception was the Trichodesmium fall maximum, when both tuft colonies and the plankton community (〈100 μm) had alkaline phosphatase activities of 0.6–7.4 μmol PNPP·μg chl a−1·h−1. Likewise, the more rare puff and bow‐tie colonies of Trichodesmium spp. in coastal waters had elevated alkaline phosphatase activities (0.8–1.6 μmol PNPP·μg chl a−1·h−1) as compared with tuft colonies coinhabiting the same waters. Intact filaments of tuft‐forming Trichodesmium sp. strain WH9601 from phosphate‐replete cultures had a base alkaline phosphatase activity of 0.5 μmol PNPP·μg chl a−1·h−1. This activity underwent a 10‐fold increase in phosphate‐deplete cultures and in cultures supplied with glycerophosphate as the sole P source. The elevated level of alkaline phosphatase activity was sustained in P‐deplete cultures, but it declined in cultures with glycerophosphate. The decline is suggested to result from feedback repression of alkaline phosphatase synthesis by the phosphate generated in the glycerophosphate hydrolysis. The enhanced alkaline phosphatase activities of Trichodesmium spp. populations provide evidence that P stress is an important factor in the ecology of Trichodesmium in the northern Red Sea.

Beschreibung: A proposal is made to standardise the reporting of Ca isotope data to the δ44Ca/40Ca notation (or δ44Ca/42Ca) and to adopt NIST SRM 915a as the reference standard.

Beschreibung: The differences in the impact of two major groups of herbivorous zooplankton (Cladocera and Copepoda) on summer phytoplankton in a mesotrophic lake were studied. Field experiments were performed in which phytoplankton were exposed to different densities of two major types of herbivorous zooplankton, cladocerans and copepods. Contrary to expectation, neither of the two zooplankton groups significantly reduced phytoplankton biomass. However, there were strong and contrasting impacts on phytoplankton size structure and on individual taxa. Cladocerans suppressed small phytoplankton, while copepods suppressed large phytoplankton. The unaffected size classes compensated for the loss of those affected by enhanced growth. After contamination of the copepod mesocosms with the cladoceran Daphnia, the combined impact of both zooplankton groups caused a decline in total phytoplankton biomass.

Beschreibung: Three arrays of ocean bottom seismographs have been deployed to study the seismicity at the northern end of the Juan de Fuca ridge system off western Canada. Nearly 100 events were located with estimated accuracies generally better than ±10 km, all lying on or near the en echalon ridge-transform fault plate boundaries as defined in this area by the magnetic anomalies, the seafloor morphology and by other geophysical data. The depths of 12 events were determined to lie between 2 and 6 km below the top of the crust. The seismograms exhibit clear P and S wave arrivals along with phases that involve P to S and sometimes S to P conversion probably at the base of the sediments beneath the instruments. The event magnitudes have been estimated from signal duration using four calibration events that were well recorded by a land station. The magnitude estimates permit the determination of rough magnitude-frequency of occurrence relations over the magnitude range of 1 to 3 that are in surprisingly good agreement with the recurrence relations for the area at larger magnitudes from 75 years of land station data. The mean P wave velocity in the uppermost mantle from the earthquake data recorded by the sea floor arrays is 7.6 km s-1 and the mean Vp/Vs ratio is 1.71 or a Poisson's ratio of 0.24.