ALBERT

Notes: Abstract Mosquito control ditches designed to increase tidal circulation are widely used as a physical control alternative to insecticidal applications The impact of such ditching on Pacific Coast marshlands was largely unknown before this five-year study of impact in two types of San Francisco Bay salt marshes, aSalicornia virginica (pickleweed) monoculure and a mixed vegetation marsh Results of our studies suggest that ditches cause less environmental disturbance than insecticidal applications The article describes the following environmental consequences of ditching for mosquito control: increased tidal flushing of soils occurs adjacent to ditches compared with that in the open marsh, thereby reducing ground water and soil surface salinities and water table height; primary productivity ofS. virginica, as determined by both the harvest method and infrared photographic analysis, is higher directly adjacent to ditches than in the open marsh, distribution of selected arthropod populations is similar at ditches and natural channels, although arthropod community response differs seasonally; aquatic invertebrate biomass is similar within ditched and natural ponds, but diversity is lower in ditched habitats, ditching increases fish diversity and density by improving fish access from tidal channels; ditches provide additional salt marsh song sparrow habitat, although ditches are less preferred than natural channels or sloughs. Management criteria can be used to design ditches that provide effective mosquito control and reduced environmental impact

Notes: Abstract Sequential sampling is a method for monitoring benthic macroinvertebrates that can significantly reduce the number of samples required to reach a decision, and consequently, decrease the cost of benthic sampling in environmental impact assessments. Rather than depending on a fixed number of samples, this analysis cumulatively compares measured parameter values (for example, density, community diversity) from individual samples, with thresholds that are based on specified degrees of precision. In addition to reducing sample size, a monitoring program based on sequential sampling can provide clear-cut decisions as to whethera priori-defined changes in the measured parameter(s) have or have not occurred. As examples, sequential sampling programs have been developed to evaluate the impact of geothermal energy development on benthic macroinvertebrate diversity at The Geysers, California, and for monitoring the impact of crude oil contamination on chironomid midge [Cricotopus bicinctus (Meigen) andC. mackenziensis Oliver] population densities in the Trail River, Northwest Territories, Canada.

Notes: Abstract Streams in mediterranean-climate regions (areas surrounding the Mediterranean Sea, parts of western North America, parts of west and south Australia, southwestern South Africa and parts of central Chile) are physically, chemically, and biologically shaped by sequential, predictable, seasonal events of flooding and drying over an annual cycle. Correspondingly, aquatic communities undergo a yearly cycle whereby abiotic (environmental) controls that dominate during floods are reduced when the discharge declines, which is also a time when biotic controls (e.g. predation, competition) can become important. As the dry season progresses, habitat conditions become harsher; environmental pressures may again become the more important regulators of stream populations and community structure. In contrast to the synchronous input of autumn litterfall in forested temperate streams, riparian input to mediterranean-type streams is more protracted, with fall and possibly spring peaks occurring in streams in the Northern Hemisphere and a summer peak existing in their Southern Hemisphere counterparts. We present 25 testable hypotheses that relate to the influence of the stream hydrograph on faunal richness, abundance, and diversity; species coexistence; seasonal changes in the relative importance of abiotic and biotic controls on the biotic structure; riparian inputs and the relative importance of heterotrophy compared to autotrophy; and the impact of human activities on these seasonally water-stressed streams. Population increases in mediterranean-climate regions (particularly in fertile regions) result in an intensification of the competition for water among different users; consequently, water abstraction, flow regulation, increased salinity, and pollution severely limit the ability of the streams to survive as sustainable, self-regulated systems.

Notes: 1. Field experiments were conducted to examine interactions between larvae of the caddisfly Gumaga nigricula and the algae (primarily diatoms) located on their sand grain cases. Floating experimental enclosures were placed in sunlit pools of a California stream. Treatments applied to occupied cases, or to those from which caddisflies had been removed, included variations in grazer density, addition of nutrients, and modification of illumination using shade cloth.2. Neither faecal-enriched agar in empty cases nor injections of faecal material into plugged cases affected case chlorophyll a concentration; injected nutrients (N and P), however, did increase chlorophyll a concentration. Faecal material may be nutrient poor, or nutrients may not be readily released. In addition, the relatively impermeable case wall may reduce the likelihood that nutrients from caddisflies reach the algae on the outer case surface.3. Although a Gumaga larva may graze algae from its own case, grazing by conspecifics and the caddisfly Helicopsyche borealis causes a greater reduction in the chlorophyll a content of cases.4. Chlorophyll a content of empty cases was decreased by experimental reduction of light. Because of shading associated with burrowing, chlorophyll a content of cases occupied by Gumaga was low and was unaffected by experimental light reduction.5. Removal of Gumaga from its case results in rapid accrual of algae. Thus, the net effect of larval presence is to diminish the algal content of its case.

Notes: SUMMARY. 1. Field experiments were conducted to examine the impact of grazing invertebrates on periphyton biomass in twenty-one pools across three northern California coastal streams (U.S.A.): Big Sulphur Creek, the Rice Fork of the Eel River, and Big Canyon Creek. Periphyton accrual on artificial substrate tiles was compared in each stream between two treatments: those elevated slightly above the stream bottom to reduce access by grazers (= platforms) and those placed directly on the stream bottom to allow access by grazers (=controls).2. Crawling invertebrate grazers (cased caddisflies and snails) were numerically dominant in each stream (86% of all grazers in Big Sulphur Creek, 61% in the Rice Fork, 84% in Big Canyon Creek). Platforms effectively excluded crawling grazers, but were less effective in excluding swimming mayfly grazers (Baetidae).3. Periphyton biomass (as AFDM) on tiles was significantly lower on controls compared to platforms for the Rice Fork, an open-canopy stream, and Big Sulphur Creek, a stream with a heterogeneous canopy. In contrast, no grazer impact was found for Big Canyon Creek, a densely shaded stream. Here, extremely low periphyton biomass occurred for both treatments throughout the 60 day study.4. The influence of riparian canopy on periphyton growth (i.e. accrual on platforms), grazer impact on periphyton, and grazer abundance was examined for Big Sulphur Creek. As canopy increased (15–98% cover), periphyton biomass on platforms decreased. In contrast, canopy had little influence on periphyton accrual on controls; apparently, grazers could maintain low periphyton standing crops across the full range of canopy levels. The abundance of one grazer species, the caddisfly Gumaga nigricula, was highest in open, sunlit stream pools; abundance of two other prominent grazers, Helicopsyche borealis (Trichoptera) and Centroptilum convexum (Ephemeroptera), however, was unrelated to canopy.

Notes: SUMMARY. Population and production dynamics of Ceraclea ancylus (Vorhies), a leptocerid caddisfly with a univoltine life cycle, five larval instars, and a single cohort population, were examined in Brashears Creek, Kentucky. A systematic sampling approach that included analysis in riffle, pool, and waterwillow bed habitats was used and fourteen sampling transects were taken across Brashears Creek between May 1971 and July 1972. For each of the 70 m2 samples taken along a transect, the depth, habitat, and substrate type were recorded. The number of C. ancylus cases and numbers and dry weights of each larval instar were determined.The majority of the C. ancylus population was in the second larval instar in July, the third larval instar in August, the fourth larval instar in September, and the fifth larval instar from October through May. The spring population was 30% of the early instar maximum estimated the previous August. The spatial distribution of C. ancylus reflects a logarithmic pattern with early instar larvae more highly clumped than the late larval instar and pupal populations. Initial standing stock estimates were less than 1% of the standing stock biomass. A production estimate of 9.9 mg/m2·year (dry weight) was determined using the instantaneous growth method, Allen's Curve method, and the Hynes method of estimating secondary production. Turnover ratios (7.0 annual TR, 5.7 cohort TR) were higher than estimates reported as typical for benthic macroinvertebrates because of the low initial to final mean individual weight of the C. ancylus larvae (0.4%).Production estimates calculated for C. ancylus populations in waterwillow bed (4.4 mg/m2·year) and pool (13.7 mg/m2·year) habitats were less than calculated for the riffle population (19.9 mg/m2·year). The annual turnover ratio (10.2) was higher in the pool population than in other habitats because of spring larval migration into the pool from other habitats. A trend of higher production estimates with larger sized substrate particles and increased numbers of particles may reflect the increase in available food sources or attachment sites. The accuracy of production estimates and their applicability to water resource management may be limited by a failure to consider the spatial distributions of the population being sampled and the tendency for sampling procedures to be confined to single habitats.

Notes: 〈list xml:id="l1" style="custom"〉1Based on information obtained from analysis of thirteen taxonomic groups of plants and animals occurring in the alluvial floodplain habitats of the Upper Rhône River, France, we synthesize results obtained on: (i) relationships among species traits; (ii) habitat utilization by species; (iii) the relationship between species traits and habitat utilization; (iv) trends in species traits in a framework of spatial and temporal variability; and (v) tests of trends predicted for species traits and species richness in the framework of spatial and temporal habitat variability in terms of the river habitat templet and patch dynamics concept.2Species traits describing reproductive characteristics, food, and size had the closest relationships with each other in the various correspondence analyses performed. Faunal and floral separation by species traits produced groupings similar to those based on traditional taxonomy.3Two major gradients appear in the utilization of the floodplain habitats: a vertical gradient from interstitial to superficial habitats; and a transverse gradient from the main channel to oxbow lakes, temporary waters, and terrestrialized habitats.4For the majority of the groups examined, a statistically significant relationship was evident between the structure of the species trait and habitat utilization arrays. For these groups, the characteristics of the habitat act as a templet for species traits. Moreover, species trait modalities (i.e. categories defining traits) were significantly arranged along the axis of spatial and temporal variability for most groups, which indicates that such variability acts as a templet for species traits.5Species traits did not conform to predictions of the river habitat templet because the observed modality sequences did not follow the trends predicted in a framework of spatial and temporal variability. Moreover, there was no clear pattern in the distribution of species traits along an axis of temporal variability for groups of organisms having different sizes, which is a correlate of longevity, nor did modalities of species traits that occur under conditions of low temporal variability also tend to occur under conditions of high spatial variability (or vice versa). Clearly, species traits occur as alternative suites of characteristics in various groups of organisms.6The patch dynamics concept, which predicts that highest species richness occurs at intermediate levels of temporal variability and highest levels of spatial variability, was supported by observations in only two of the thirteen groups exaniined, and only partially (for spatial variability) when all 548 taxa were examined together.7The predictions of the river habitat templet and patch dynamics concepts were not supported, perhaps because templet theories do not yet accommodate alternative suites of characteristics and trade-offs between combinations of traits, or perhaps because the single scale of variability considered in the analyses, the inhomogeneity of the available biological information, and the aggregation of spedes traits that were used created methodological problems.8Ecologically sound river management polides eventually may be based on two key points that emerged from this synthesis: that the habitat acts as a templet for spedes traits, and that composite taxonomic groupings represent relatively homogeneous assemblages of spedes trait modalities.9The use of statistical approaches developed in this project to analyse other long-term data sets may clarify questions about the applicability of habitat templet theories to river ecology, and hasten development of ecologically sound river management policies.

Notes: 1. Allozyme electrophoresis was used to describe the genetic structure of Helicopsyche borealis caddisflies collected from three sites in each of three streams in northern California, U.S.A.: the Rice Fork of the Eel River; Big Sulphur Creek; and Alameda Creek. Between 7 and 11km separated adjacent sites within these three streams. Helicopsyche borealis from three additional streams in eastern North America (Christiana Creek, Indiana; Byrd's Mill Creek, Oklahoma; Susquehanna River, Pennsylvania) were also analysed electrophoretically to address taxonomic questions that arose during the study.2. Four genetically distinct groups of individuals were identified (i.e. Helicopsyche types A, B, C, and D). Lack of interbreeding between sympatric groups (as evidenced by fixed allelic differences) and large genetic differences (mean Nei's genetic distances = 0.396–0.693) indicate that these four groups of Helicopsyche were actually reproductively isolated species rather than genetic variants of a single species.3. Occurrence of Helicopsyche type A at multiple sites permitted an analysis of spatial variation in genetic structure. Within a drainage basin, small differences in allele frequencies were observed among sites in the Rice Fork and Big Sulphur Creek, but not in Alameda Creek. Larger genetic differences were found among sites in separate drainage basins. Genetic distances (Nei's) between Helicopsyche type A from California and from eastern North America sites (mean = 0.236) were greater than interpopulation differences commonly observed for insects, which suggests that Helicopsyche type A from California may represent a different species than Helicopsyche type A from eastern North America.4. Geographical and taxonomic differences observed in this study underscore the importance of understanding both population structure and genetic relationships among populations in the design and interpretation of stream faunal studies.

Notes: 1. International collaboration in freshwater ecology was examined using authorship affiliations of articles published in thirty-three specialized journals. Most are published in Europe.2. Researchers from four to thirty-seven different countries were represented in the 100 articles examined for each journal. Only 29% of articles were single-authored; multicountry authors' addresses (indicating international collaboration) were found for 9% (range 0–23% per journal) of articles examined.3. Five of the eighty-nine countries listed in the addresses of the 3300 articles together contributed 〉50% of total articles: United States (24.9%), Canada (8.6%), Germany (7.6%), Commonwealth of Independent States (7.0%) and Poland (5.9%). Of the fifteen countries that each produced 〉2.5% of total articles, the percentage representing international collaboration was highest for France (34.9%) and Canada (24.0%). The seventy-four countries that each contributed 〈2.5% of total articles generally had higher rates of international collaboration.4. Researchers in the United States and Canada collaborate internationally almost twice as often in freshwater ecology than in all science. Much of France's extensive international collaboration is with countries that produce few articles in freshwater ecology, and their international collaboration is often exclusively with France.5. Three journals publishing both marine and freshwater ecology articles contain more articles on the former topic, but more countries are represented in the publication of freshwater than marine research.6. The percentage of articles that represent international collaboration is higher in freshwater ecology than in medicine, biology, chemistry and engineering, and approximates that in physics.

Notes: 〈list xml:id="l1" style="custom"〉1Using sites from the Upper Rhône River, France, as an example, the objective of this paper is to identify the essential elements needed to test current ecological theories with previously collected data. Procedures developed may enable other groups to design comparable research strategies for syntheses of long-term studies of ecological systems.2Because of the high number (more than 200) and turnover of researchers, the long study period (about 17 years), the evolution of research methods and interests, and the diverse systematic groups that were considered (from micro-organisms to birds), the data available for a synthesis were quite heterogeneous. The application of a ‘fuzzy coding’ technique allowed such disparate information to be structured for analysis.3The habitat templet concept and the patch dynamics concept were selected for analysis with existing data on the Upper Rhône because theories, such as these, that link ecological responses to habitat templets are a focus of current ecological debate and potentially may serve as a general tool for ecologically orientated river management.4A preliminary trial to structure the existing knowledge, to identify (and manage) gaps in it, and to create and apply the analytical tools in a way that predictions from theory could be tested was an essential element in the design of this project.5Predictions derived from the theoretical concepts had to match the format of the available information on the Upper Rhône; potential bias was avoided by having a priori predictions developed by previously uninvolved colleagues.6Synthesis of the long-term study of the Upper Rhône in the context of concurrently developed ecological theory required, at times, an unconventional research strategy. Hence, the generation of hypotheses and methods, the presentation of results, and consequently the discussions in papers of this special issue of Freshwater Biology (Statzner, Resh & Dolédec, 1994) represent an innovative approach to testing ecological theory.