bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term changes in the assemblage of demersal fishes and invertebrates in relation to environmental variations in Tokyo Bay, Japan
Authors: KODAMA K. , AOKI I. , SHIMIZU M. , TANIUCHI T.
Published: March 2003

Abstract Long‐term changes in the demersal assemblage, including both fishes and invertebrates, in Tokyo Bay, Japan, were examined between 1977 and 1995. A total of 255 species were collected, of which 113 were regarded as representative in terms of occurrence. Multivariate analyses of the representative species showed that fluctuations in the catch were related to three periods that reflected changes in relative abundance and species composition. In particular, mantis shrimp, Oratosquilla oratoria (de Haan), whipfin dragonet, Repomucenus valenciennei (Temminck & Schlegel), and marbled sole, Pleuronectes yokohamae Günther, showed high dominance in the mid‐1980s. Discriminant analysis suggested that the demersal assemblage changed synchronously with environmental conditions. Causes of the temporal changes in the demersal assemblage in relation to variations in environmental factors are discussed.
Feeding activities of zooplankton in the Bohai Sea
Authors: WANG RONG , LI CHAOLUN , WANG KE , ZHANG WUCHANG
Published: March 2003

The Bohai Sea was the site of the Chinese national GLOBEC programme. During the June 1997 cruises of R/V Science No.1, observations and experiments on zooplankton feeding were conducted. At five 48 h time‐series stations the following observations and measurements on zooplankton were carried out: (1) diurnal vertical migration, by collecting samples at different layers every 3 h with a closing net; (2) diurnal feeding rhythms, by gut pigment analysis; and (3) ingestion rate, by both gut pigment analysis and the dilution method. A classification by body size was used to deal with the diversity of species and developmental stages of zooplankton assemblages. Samples were separated into three size groups: small (200–500 μm), medium (500–1000 μm) and large (> 1000 μm). The results showed that the copepods (Calanus sinicus, Paracalanus parvus, Acartia bifilosa and Centropages mcmurrichi) performed clear diurnal vertical migrations. However, their behaviour was different at different stations. The variation in gut pigment content over the 24 h cycle showed strong diurnal feeding rhythms, particularly for the large size group. Gut pigment contents reached their daily maximum during the time from dusk to midnight (18:00–24:00). The peak value was about 10 times the minimum observed in the daytime. The in situ daily grazing rate, based on gut pigment contents and evacuation experiments, was 4.00–12.65 ng chla ind−1 day−1 for the small size group, 5.99–66.58 ng chla ind−1 day−1 for the medium size group and 31.31–237.13 ng chla ind−1 day−1 for the large size group. The copepods consumed only a small part (2.90–13.52%) of the phytoplankton biomass but about 77% of the daily production. The grazing mortality rate of phytoplankton by microzooplankton (< 200 μm) measured by the dilution method ranged from 0.43 to 0.69 day−1 The calculated daily consumption of phytoplankton biomass was 35–50%, and 85–319% of the potential production.
Larval transport during winter in the SABRE study area: results of a coupled vertical larval behaviour–three‐dimensional circulation model
Authors: Hare  , Quinlan  , Werner  , Blanton  , Govoni  , Forward  , Settle  , Hoss
Published: March 2003

A three‐dimensional circulation model was used in conjunction with larval fish vertical behaviour models to study the interaction between larval vertical distribution, advection and the outcome of larval transport along the central portion of the east coast of the United States. The circulation model was forced by tides, a northern boundary inflow, and winds. Vertical behaviour models were developed for Atlantic menhaden (Brevoortia tyrannus) and spot (Leiostomus xanthurus). The purpose of this modelling effort was to investigate the transport pathways of Atlantic menhaden and spot larvae from offshore spawning grounds to estuarine nursery habitats. The coupled circulation and behavioural model demonstrated the importance of along‐shelf transport in what is generally thought to be a ‘cross‐shelf’ problem. Cross‐shelf transport was associated with bathymetric features, such as shoals. Both physical (e.g. wind) and biological (e.g. changes in larval behaviour) events were responsible for many of the observed patterns in larval transport. Overall, larval transport was determined by circulation but was modified by larval vertical distributions.
Exchange and flux of larval fishes across the western Gulf Stream front south of Cape Hatteras, USA, in winter
Authors: Govoni  , Spach
Published: March 2003

To describe exchange and to frame the magnitude of the flux of larval fishes across the Gulf Stream front in winter, collections were taken on the inshore and offshore sides of the frontal zone in 1991, 1993, 1994 and 1995, off Onslow Bay, North Carolina. Collections yielded larval fishes representing 75 families. Of these, the larvae of the families Gonostomatidae or Phosichthyidae consistently occurred on both sides of the frontal zone, yet are exclusively of mesopelagic, deep‐oceanic origin; hence, they indicate Gulf Stream‐to‐shelf water‐exchange. The larvae of the clupeid, Brevoortia tyrannus, and the sciaenid, Leiostomus xanthurus, occurred on both sides of the frontal zone, yet spawn on the outer continental shelf in or near the Gulf Stream front; hence these taxa indicate shelf‐to‐Gulf Stream water‐exchange. The mechanisms of exchange, as indicated by the distribution of heat and salt across the front, along with satellite images of sea‐surface temperature, were not completely resolved, largely because of the two‐dimensional (x, z) rather than three‐dimensional (x, y, z) coordination employed. The observed distributions of indicator taxa did not always conform with expected, given the distribution of heat and salt across the front. Parcels of water exchanged across the front upstream (to the south) and encountered during observation along the cross‐shelf transects explains the lack of conformity. Where the expected and observed distributions agreed, the flux was 0.0009 larvae m−1 s−1 for the indicators of Gulf Stream‐to‐shelf exchange, and 0.0007–0.0030 larvae m−1 s−1 for the indicators of shelf‐to‐Gulf Stream exchange.
Applications of SABRE to research and management
Authors: Crowder  , Hoss
Published: March 2003

In this paper, we highlight the major results from the SABRE programme and applications to research and management. In particular, SABRE provided new scientific insights into the fisheries oceanography of the estuarine‐dependent fishes of the South Atlantic Bight. Although we concentrated our efforts on Atlantic menhaden, we also gained insights on the coupling of physics to biology in the early life history of a number of marine fishes. Larval transport from spawning sites to and through barrier island inlets is now better understood. Analysis of menhaden population dynamics suggests survival in the late larval/early juvenile stage is particularly important to population growth. This phase of the life history appears likely to present a bottleneck to recruitment for Atlantic menhaden. We also made a number of technological breakthroughs which are already being applied elsewhere in research and assessments including the Continuous, Underway Egg Sampler (CUFES), enzyme‐based approaches to evaluating condition of individual larvae and various physical and biological modelling innovations. Our experiences establishing and managing the SABRE research team also provide insights into one model for promoting multidisciplinary research in fisheries oceanography. Throughout SABRE, we have sought an open exchange of information and insights from a wide variety of researchers and environmental managers. We hope the synthesis provided here continues that dialogue.
From spawning grounds to the estuary: using linked individual‐based and hydrodynamic models to interpret patterns and processes in the oceanic phase of Atlantic menhaden Brevoortia tyrannus life history
Authors: Quinlan  , Blanton  , Miller  , Werner
Published: March 2003

Present theory suggests that population regulation in marine fishes cannot be resolved until an understanding of the processes involved in shaping the overall distribution (the number of populations, geographical extent, mean abundance and temporal changes in abundance) is developed. Here, we present a step toward understanding Atlantic menhaden population patterns, by studying processes in the Middle and South Atlantic Bights, which shape those patterns. We use individual‐based and hydrodynamic models to reinterpret the ‘mechanics’ of the menhaden life history, and put forward several potentially testable hypotheses. The success of the menhaden reproductive strategy seems to depend on the seasonal changes in the mean flow field of the Middle and South Atlantic Bights, suggesting that their life history may have been strongly structured by the regional physics of the system. Because the annual menhaden migration is size‐based and spawning occurs throughout the population’s range, the size distribution of the adult population may influence the supply of larvae to particular estuaries along the coast. Recruitment of larvae into Delaware and Chesapeake Bays may be dependent on spawning to the north of the bays’ mouths, owing to coastline shape and orientation in the vicinity of the bays. Our results suggest that management of this resource might be improved by consideration of the spatial and temporal variability in both the biological and the physical system.
Changes in the distribution of Atlantic cod (Gadus morhua) in the southern Gulf of St Lawrence — effects of environmental change or change in environmental preferences?
Authors: SWAIN DOUGLAS P.
Published: March 2003

Density‐independent redistribution in response to changing temperature conditions and density‐dependent redistribution in response to changing temperature preferences are two contrasting hypotheses to explain changes in the distribution of cod populations. I tested these hypotheses using survey data on the distribution of cod during the feeding season in the southern Gulf of St Lawrence. These tests used indices of cod distribution as the dependent variable and indices of cod abundance and bottom temperature as explanatory variables. Both hypotheses were often supported in univariate tests that ignored confounding between the two explanatory variables. Tests that accounted for this confounding indicated an effect of cod abundance on distribution for ages 4–8+ years, and 3+, but provided no support for an effect of environmental conditions on distribution except for age 3. Variation in the temperature distribution of cod was consistent with an effect of abundance on interannual variation in distribution and with no effect of environment except for age 3 cod. Age 3 cod were consistently under‐represented in areas of very cold bottom water but older cod were not. As predicted by bioenergetic considerations, cod tended to occupy colder water at high levels of abundance, suggesting a mechanism for density‐dependent shifts in distribution. Shifts in cod distribution during the feeding season in the southern Gulf appear to be more closely linked to density‐dependent changes in environmental preferences than to density‐independent responses to changing environmental conditions.
Depth, temperature and salinity preferences of newly recruited penaeid shrimps in Kuwait waters
Authors: YE YIMIN , MOHAMMED  , BISHOP
Published: March 2003

Associations between catches and depth, temperature and salinity data obtained from the 1994–97 preseason shrimp trawl surveys in Kuwait waters were analysed using cumulative distribution functions and overlap coefficients. No single environmental factor had a controlling influence on shrimp distribution. Shrimp associations with the joint distributions of two environmental variables were stronger and more consistent over time than those with any single environmental factor. All three shrimp species examined in this study were significantly associated with the joint distributions of depth and temperature, and depth and salinity, indicating depth as the most influential factor in structuring the shrimp distributions during the surveys. Metapenaeus affinis and Parapenaeopsis stylifera were distributed at similar ranges of depth (8–15 m), temperature (26–31°C) and salinity (35–41‰), and had very high overlap coefficients. These two species can be categorized as co‐occurring species in the sampled area. Penaeus semisulcatus had the widest range of the three environmental variables investigated in this study, particularly depth (8–32 m) and temperature (24–32°C).
Turtles on the edge: movement of loggerhead turtles (Caretta caretta) along oceanic fronts, spanning longline fishing grounds in the central North Pacific, 1997–1998
Authors: Polovina Jeffrey J. , Kobayashi Donald R. , Parker Denise M. , Seki Michael P. , Balazs George H.
Published: March 2003

Nine juvenile loggerhead sea turtles tracked during 1997 and 1998 in the central North Pacific by satellite telemetry all travelled westward, against prevailing currents, along two convergent fronts identified by satellite remotely sensed data on sea surface temperature (SST), chlorophyll and geostrophic currents. These fronts are characterized by gradients in sea surface height that produce an eastward geostrophic current, with gradients in surface chlorophyll and SST. Six of the turtles were associated with a front characterized by 17°C SST, surface chlorophyll of about 0.2 mg m–3, and eastward geostrophic current of about 4 cm s–1, while the other three turtles were associated with a front with 20°C SST, surface chlorophyll of about 0.1 mg m–3, and eastward geostrophic flow of about 7 cm s–1. These results appear to explain why incidental catch rates of loggerheads in the Hawaii longline fishery are highest when gear is set at 17°C and 20°C, SST. Further, from the seasonal distribution of longline effort relative to these fronts, it appears that the surface longline fishing ground lies largely between these two fronts during the first quarter and well to the south of the 17°C front, but including the 20°C front, in the second quarter. These findings suggest seasonal or area closures of the longline fishery that could be tested to reduce incidental catches of loggerheads. Finally, these results illustrate the insights which can be achieved by combining data on movement of pelagic animals with concurrent remotely sensed environmental data.
Ecophysiological diversity of alpine populations of Gammarus lacustris in relation to environmental calcium
Authors: Meyran J. ‐C.
Published: March 2003

1. The contribution of environmental calcium to ecophysiological diversity among populations of Gammarus lacustris was investigated by comparing five alpine lakes in France.

2. Calcium concentrations in the water varied with substratum lithology, ranging from 6 mg L–1 in lakes on crystalline (igneous) rocks to 32.7 mg L–1 in lakes on limestone, and up to 248 mg L–1 in a lake with a gypsum environment.

3. The duration of the moult cycle and mortality rate were compared between populations by means of field and in situ laboratory and translocation experiments on adult males. Animals from water with low calcium concentrations showed a significantly longer moult cycle and higher mortality rate than those from water with high calcium concentrations. A significant increase in the duration of the moult cycle was observed in animals translocated to water of lower calcium concentration and vice versa.

4. These results suggest the existence of different physiological races of G. lacustris with an ecophysiological plasticity of calcium metabolism narrower than that of river‐dwelling gammarids such as G. fossarum. This may be a consequence of geographic isolation among lacustrine populations together with the relatively stable environmental parameters in lakes.
Seasonal changes in planktonic bacterial assemblages of two Ohio streams
Authors: Leff Laura G. , Leff Adam A. , Lemke Michael J.
Published: March 2003

1. Monthly water samples were collected from two Ohio streams (Bixon and Mahoning) for 14 months to assess the extent of seasonal changes in the bacterial assemblage and in a population within the assemblage. At the assemblage level, abundances of total bacteria and colony forming units (CFUs) were measured. Populations of Burkholderia (Pseudomonas) cepacia were quantified by colony hybridization using a species‐specific rDNA probe.

2. Total bacterial numbers were highest in early winter and were lowest during summer and when the streams were covered with ice. Changes in the number of CFUs were more variable than changes in total number, but did not exhibit a clear seasonal pattern.

3. B. cepacia was not detected during summer, but up to 8000 ml–1 were present in November. Seasonal changes in assemblage‐level measurements were dissimilar to population‐level changes in B. cepacia abundance.

4. The temporal changes observed in this study suggest that populations of stream bacteria, such as B. cepacia, exhibit seasonal blooms that are undetected by assemblage level measurements.
An application of the plaster dissolution method for quantifying water velocity in the shallow hyporheic zone of an Appalachian stream system
Authors: Angradi Ted , Hood Robert
Published: March 2003

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.
Aquatic insects in an estuarine environment: densities, distribution and salinity tolerance
Authors: Williams D. Dudley , Williams Nancy E.
Published: March 2003

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.
Application of an index of biological integrity (IBI) to fish assemblages of the rivers Khan and Kshipra (Madhya Pradesh), India
Authors: Ganasan V. , Hughes Robert M.
Published: March 2003

1. A multimetric index of fish assemblage integrity was developed and similarity analyses were conducted on fish species in two central Indian rivers and the effects of distance from municipal and industrial effluents on those indices then evaluated.

2. Five metrics from Karr et al. (1986
, Illinois Natural History Survey Special Publication 5, Urbana, IL) were adopted: intolerant species richness, % omnivorous individuals, % top carnivore individuals, total number of individuals and % individuals with anomalies. Seven new metrics (native species richness, native family richness, benthic species richness, water column species richness, % non‐native individuals, % tolerant individuals and % herbivorous individuals) were added.

3. Non‐native individuals represented 1–55% of the assemblages at sampled sites which held fish.

4. Fish were present at eleven sites and not collected at two sites, despite heavy metal concentrations exceeding U.S. Environmental Protection Agency acute criteria at all sites.

5. Two types of metric scoring were examined. The traditional 5–3–1 method showed the same pattern as continuous scoring from 0 to 10, but produced a higher integrity class at one site.

6. Scores on our modified index of fish assemblage integrity increased with distance downstream from a major effluent source in each river. Jaccard similarity scores between the least disturbed downstream site and all other sites decreased with increasing distance and disturbance.

7. It was concluded that Karr’s original index and its theoretical foundations are easily adaptable, even to an ichthyofauna containing no species, and only two families (Cyprinidae, Poeciliidae), in common with the midwestern United States.
Migratory drift of larval freshwater shrimps in two tropical streams, Puerto Rico
Authors: March J. G. , Benstead J. P. , Pringle C. M. , Scatena F. N.
Published: March 2003

1. Migratory shrimps are often major biotic components of tropical stream communities, yet spatial and temporal patterns of their migration have yet to be described. This information is of increasing importance given the continued fragmentation of tropical streams by damming and water abstraction/diversion, which can disrupt migratory life cycles.

2. Larval amphidromous shrimps are released by adult females in freshwater streams. They then drift passively to an estuarine habitat where they metamorphose before migrating back upstream. Drift of larval shrimps was sampled over two to five 24‐h periods at each of three sites along two rivers that drain the Luquillo Experimental Forest in Puerto Rico: the Espíritu Santo (10, 135 and 335 m a.s.l.) and the Mameyes (10, 90 and 290 m a.s.l.). A total of seventeen diel samplings were conducted.

3. Shrimp drift increased in the downstream direction in both catchments, and had a significant positive exponential relationship with length of stream channel above each site. There was no significant difference between catchments with respect to mean daily drift rate per km of stream channel. Maximum observed larval shrimp density was 69 102 larvae 100 m–3 (1.7 g dry mass 100 m–3), which is high relative to published invertebrate drift studies.

4. The pattern of shrimp drift agreed with the ’risk of predation hypothesis‘. In stream reaches with predatory fish, drift of larval shrimps occurred at night and was slight during the day. A nocturnal peak in drift occurred between 19.00 and 22.00 h. At a high‐altitude site, where predatory fish were absent, no diel pattern was discernible.

5. The present study provides information on the timing of migratory drift of larval shrimps, which can minimize the adverse effects of water abstraction from streams draining the Luquillo Experimental Forest. Elimination of water withdrawal during peak larval drift after dark will significantly reduce shrimp mortality.
The impact of flash floods on microbial distribution and biogeochemistry in the parafluvial zone of a desert stream
Authors: Holmes Robert M. , Fisher Stuart G. , Grimm Nancy B. , Harper Bryan J.
Published: March 2003

1. The impact of flash flooding on microbial distribution and biogeochemistry was investigated in the parafluvial zone (the part of the active channel lateral to the surface stream) of Sycamore Creek, a Sonoran Desert stream in central Arizona.

2. It was hypothesized that subsurface bacteria were dependent on the import of algal‐derived organic matter from the surface stream, and it was therefore predicted that microbial numbers and rates of microbially mediated processes would be highest at locations of surface to subsurface hydrologic exchange and at times when algal biomass was high.

3. Prior to a flash flood on 19 July 1994, chlorophyll a was high (≈ 400 mg m–2) in the surface stream and microbial numbers were highest at the stream–parafluvial interface and declined along parafluvial flowpaths, supporting the hypothesized algal–bacterial linkage. Immediately following the flash flood, chlorophyll a was low (≈ 7 mg m–2), and microbial numbers were reduced at the stream–parafluvial interface.

4. Counter to expectations, parafluvial functioning (in terms of nitrate production and dissolved oxygen decline along flowpaths) re‐established immediately after the flood receded. Therefore, material other than algal exudates supported parafluvial metabolism immediately postflood, and terrestrially derived dissolved organic matter is the likely source.

5. Algae in the surface stream recovered quickly following flooding, but recovery of parafluvial bacteria lagged somewhat behind. These results highlight the importance of surface–subsurface interaction to stream ecosystem functioning and show that the nature of these interactions changes substantially in successional time.
Estimating the effective clearance rate and refiltration by zebra mussels, Dreissena polymorpha, in a stratified reservoir
Authors: Yu Neng , Culver David A.
Published: March 2003

1. The grazing impact of zebra mussels, Dreissena polymorpha Pallas, is often evaluated by applying the individual filtration rate measured in the laboratory to the field abundance and then by comparing the total volume of water filtered with the whole lake volume. Since this approach overlooks refiltration, it overestimates the grazing impact of zebra mussels. To deal with this problem, the present authors developed an in situ method for collecting faeces and pseudofaeces to measure the actual volume of water that is cleared of suspended particles by Dreissena in a unit time under a given set of environmental conditions. This is termed the effective clearance rate (ECR).

2. The experiment was conducted in Hargus Lake, OH, U.S.A., a small thermally stratified reservoir, to test the effects of spatial aggregation, mussel density and the concentration of particulate inorganic matter (PIM) on the effective clearance rate of Dreissena.

3. Over 40 measurements, the ECR values ranged from 15.3 to 68.6 mL ind−−1 h−−1. Much of the variation can be explained by colony form, mussel density and seston concentration. The effects of these variables were all statistically significant. The average ECR for isolated individuals was higher than that for those in clumps (40.4 versus 32.8 mL ind−−1 h−−1), which is attributed to increased refiltration in the cores of the clumps. The ECR decreased with increased zebra mussel density because of intensified competition for food particles within the group. The ECR increased with increased PIM concentration in the lake water, which may be interpreted as a result of enhanced water mixing which ultimately caused increases in both sediment resuspension and particle delivery to the mussels.

4. Taking the filtration rates for a 20‐mm mussel to be between 116 and 234 mL ind−−1 h−−1, based on data from the literature, the clumped mussels under the present experimental conditions would have a refiltration ratio between 3.4 and 6.9.

5. The present authors developed an areal clearance model which predicts that seston removal by the Dreissena population is limited by the particle delivery from the ambient water to the mussel bed and will reach a maximum value beyond which no further increase will occur with increased population density.

6. It is concluded that the direct grazing impact of zebra mussel on phytoplankton in thermally stratified lakes is much less effective than predicted from simple filtration rate estimation.
Pectoral fin size in a fish species with paternal care: a condition‐dependent sexual trait revealing infection status
Authors: Bakker Theo C. M. , Mundwiler Beat
Published: March 2003

1. The three‐spined stickleback, Gasterosteus aculeatus L., is a territorial fish with exclusive male parental care. Males oxygenate the eggs with fanning movements of their pectoral fins. The present authors investigated whether the apparent sexual differences in the functional demands of the pectoral fins have resulted in sexual differences in fin size. If males have relatively larger pectoral fins, females may use this as a signal to aid their mate choice for good fathers. Therefore, further objectives were to study the condition‐dependency of relative pectoral fin size in males and the relationship with male parasite load.

2. Reproductively active males possessed relatively larger pectoral fins than females in both wild‐caught and laboratory‐bred fish.

3. In the field, caring males with relatively large pectoral fins were in better physical condition and had more food in their stomachs.

4. Relatively small pectoral fins and poor body condition were associated with infection by the intestinal parasite Pomphorhynchus laevis (Acanthocephala), the prevalent parasite species in the study population.
Periphyton removal related to phosphorus and grazer biomass level
Authors: Anderson E. L. , Welch E. B. , Jacoby J. M. , Schimek G. M. , Horner R. R.
Published: March 2003

1. The proliferation of nuisance periphyton in enriched streams may be dependent on the biomass of the grazing macroinvertebrates present. In the present study, the effectiveness of grazer size and biomass in controlling periphyton and the extent to which grazing effectiveness was affected by enrichment level were determined.

2. Two sets of experiments with two caddisfly grazers were conducted in laboratory channels during spring and summer 1995 and 1996. The first set tested the combined effect of phosphorus enrichment and grazing, while the second set tested the effect of variable grazer biomass on periphyton biomass.

3. Grazing reduced periphyton biomass in excess of 80%, compared to ungrazed controls. Grazers were equally effective in controlling filamentous green algae, Stigeoclonium, diatoms and small colonial greens. Near complete removal of periphyton biomass by grazing occurred at even at the lowest grazer biomass level (750 mg m−−2, i.e. approximately one‐third of natural levels).

4. Grazing controlled periphyton biomass more than did enrichment with soluble reactive phosphorus (SRP).

5. Grazing rates in the phosphorus‐grazing interaction experiments averaged about 6 mg chl a g invertebrate−−1 day−−1, which was similar to past work in these channels and elsewhere, while rates were about five‐fold higher in the variable grazer biomass experiments.

6. Simulating effects of SRP and grazing with a calibrated model suggests that higher SRP levels would be necessary to exceed a nuisance periphyton biomass level if grazers were present. However, if grazer biomass was more than 1500 mg m−−2, a nuisance level would probably not be exceeded at any SRP.
Establishing the condition of lowland floodplain rivers: a palaeo‐ecological approach
Authors: Thoms M. C. , Ogden R. W. , Reid M. A.
Published: March 2003

1. Current approaches for determining river ‘health’ rely on the establishment of a ‘reference’ condition. This is often difficult to achieve for lowland floodplain river systems because of the lack of pristine or pre‐impacted sites and process models capable of predicting the effect of natural and human disturbances.

2. Using examples from the River Murray, Australia, this paper highlights the benefits of using palaeo‐ecological studies in deciding on benchmark or pre‐European settlement conditions for lowland floodplain river systems.

3. Physical, chemical and biological analyses of sediment obtained from shallow cores (< 2 m) extracted from a variety of floodplain sites on the River Murray and its tributaries reveal the extent and timing of catchment disturbances on this lowland river. Rates of sedimentation have increased by an order of magnitude since settlement; sediments now being deposited are finer, having implications for the nutrient status of the floodplain and the accumulation of heavy metals associated with these sediments. There has also been a sustained drop in the macrophyte cover of billabongs in the area, as inferred by chydorid cladoceran assemblages. The pre‐European settlement diatom assemblages do not resemble those presently accumulating in billabongs in the region.

4. Whilst initially developed for lentic studies, palaeo‐ecological studies are relevant to the establishment of benchmark conditions for lowland floodplain rivers. They are relatively straightforward, incorporate both historical and contemporary ecological information and can be applied to any lowland system.
Invasion of North American drainages by alien fish species
Authors: Gido Keith B. , Brown James H.
Published: March 2003

1. Data from the literature were used to document colonization patterns by introduced freshwater fishes in 125 drainages across temperate North America. We analysed this data set to quantify susceptibility to invasion, success of the invaders and changes in species richness.

2. Drainages with a high number of impoundments, large basin area and low native species diversity had the greatest number of introduced species. Those drainages containing few native fishes exhibited great variation in the number of invaders, while waters with a rich native fauna contained few introduced species. However, this pattern did not differ significantly from random simulations because the pool of potential invaders is greater for drainages with low species richness.

3. In most drainages, there were more introduced than imperilled or extirpated species, suggesting that invaders tend to increase overall species richness.

4. These patterns suggest that North American fish communities are not saturated with species, but instead, are capable of supporting higher levels of diversity if the pool of potential colonists and the rate of colonization from that pool is increased.
Crowding‐induced changes in growth, reproduction and morphology of Daphnia
Authors: Burns Carolyn W.
Published: March 2003

Daphnia may reach high population densities seasonally, or in patches, in lakes. To test the effects of chemicals released by high daphniid densities on their life‐history traits, nine species of Daphnia, D. magna, D. pulicaria, D. pulex, D. hyalina, D. galeata, D. laevis, D. lumholtzi, D. ambigua and D. cucullata, were grown in water from crowded Daphnia cultures in a flow‐through system in the presence of abundant food.

Water from Daphnia at 85 L‐1 depressed growth rate, and lowered body size and clutch at first reproduction of six species of small‐bodied Daphnia (adult body length < 1.8 mm), but had no significant effects on larger species. Two clones of D. pulex differed in their growth rate in response to crowding, indicating that response patterns may vary within species.

Chemicals released by crowded D. magna reduced tail spine length in D. lumholtzi and D. cucullata by 37% and 11%, respectively, and induced changes in carapace morphology in D. lumholtzi and D. ambigua.

Chemicals released by crowded conspecifics may provide an additional, density‐dependent mechanism of population regulation; when large species of Daphnia coexist at a high population density with small species, these chemicals may reinforce the competitive advantage of large species.
Minimal models of top‐down control of phytoplankton
Authors: Scheffer Marten , Rinaldi Sergio
Published: March 2003

1. A set of models describing the dynamics of top‐down control of phytoplankton by Daphnia in lakes is reviewed. The basis of these models is a simple and well‐known model that has been used, among other things, to demonstrate the paradox of enrichment.  2. We discuss minimal extensions that allow this model to mimic the effects of spatial heterogeneity, planktivory, seasonality and inedible algae.  3. These models generate hypotheses about mechanisms that may cause patterns observed in the field such as:

Spatial heterogeneity stabilizes plankton dynamics, and causes enrichment to result in a gradual increase of both zooplankton and algal biomass.

Daphnia populations can collapse at a threshold level of predation pressure from fish, rather than gradually become less abundant.

Absence of Daphnia in summer may typically be caused by the combination of food shortage followed by suppression by fish.

The spring clear‐water phase and various other aspects of the typical seasonal dynamics of Daphnia and algal biomass can simply be explained from the seasonal rise and fall of rates of biological processes and the reproduction cycle of fish.

Depending on the conditions, cyanobacterial dominance can be stimulated but also suppressed by Daphnia.

4. We discuss the way in which such very simple models may contribute to the building of theories about plankton dynamics in the field, and the caveats of interpreting wrongly the message from models.
Role of transported particulate organic matter in the macroinvertebrate colonization of litter bags in streams
Authors: Dangles Olivier , Guerold François , Usseglio‐Polatera Philippe
Published: March 2003

1. The exposure of mesh litter bags has been widely used to investigate the role of benthic macroinvertebrates in leaf processing in freshwaters. In this sense, several studies have related litter bag breakdown rates to the presence of colonizing invertebrates. A possible confounding factor in such experiments is that the litter bags trap suspended particulate organic matter that can itself attract invertebrate colonists, irrespective of the intended experimental treatment.

2. We attempted to quantify the accumulation of particulate organic matter (POM) within litter bags and to investigate its possible impact on macroinvertebrate density and richness. In seven headwater forested streams we exposed mesh bags filled either with beech leaves (Fagus sylvatica) or with plastic strips of an equal surface area.

3. Principal component analysis (PCA) showed that bag type and stream were the main explanatory variables for invertebrate colonization and POM accumulation within the bags. In contrast, there was little variation among sampling dates (6.4% of the total inertia).

4. The accumulated POM within the bags was substantial (up to 8.83 g ash‐free dry mass (AFDM)) but highly variable among sites (mean from 0.32 to 4.58 g AFDM). At each of the seven sites, both richness and abundance of invertebrates were positively correlated with the mass of accumulated POM in bags. Macroinvertebrate colonization (notably taxon richness) was directly linked with the quantity of POM accumulated.

5. Our findings provide evidence of a potential pitfall in linking invertebrates to litter processing in mesh bags, particularly when large amounts of POM, entrained in stream flow, accumulate within the bags. An evaluation of the POM mass trapped in litter bags could account for the erratic patterns sometimes observed in their colonization by invertebrates.
Response of bacterial extracellular enzymes to inundation of floodplain sediments
Authors: Burns A. , Ryder D. S.
Published: March 2003

1. Bacterial extracellular enzymes provide a measure of microbial response to organic matter supply, pivotal to the recovery of riverine food webs after disturbances such as floods.

2. We examined the effects of flood duration on extracellular enzyme response from riverbank and floodplain wetland sediments from the Murrumbidgee River, south‐east Australia.

3. There were strong temporal peaks in enzyme activity from both riverbank and billabong sites, peaking between 1 and 5 days following flooding and with a general decline by 21 days. A dominance of non‐glucosidase and xylosidase enzymes resulted in no significant differences between billabong and riverbank sediments. This supports the hypothesis that regulated Australian river systems are driven by autochthonous carbon sources.

4. The short response time of the glucosidase after flooding suggests that even short pulses (24 h) in high flows may stimulate bacterial activity, as dissolved organic carbon (DOC) loads also peak at this time. However, a longer wetting time may be needed to drive hydrolysis of the proteins, fatty acids and longer chain polysaccharides, whether in the littoral zone of the river or connection with the floodplain.
Spatio‐temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps
Authors: Robinson C. T. , Uehlinger U. , Hieber M.
Published: March 2003

1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity.

2. Nitrogen concentrations were high (nitrate‐N values were 130–274 μg L–1), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m–2 dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus.

3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m–2, although peaking as high as 9000 ind. m–2. Average annual biomass ranged from 102 to 721 mg m–2, and reached >2000 mg m–2 at one site in autumn.

4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina, and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer.
Mass loss and macroinvertebrate colonisation of Pacific salmon carcasses in south‐eastern Alaskan streams
Authors: Chaloner Dominic T. , Wipfli Mark S. , Caouette John P.
Published: March 2003

1. We examined the spatial and temporal dynamics of pink salmon (Oncorhynchus gorbuscha) carcass decomposition (mass loss and macroinvertebrate colonisation) in south‐eastern Alaskan streams. Dry mass and macroinvertebrate fauna of carcasses placed in streams were measured every two weeks over two months in six artificial streams and once after six weeks in four natural streams. We also surveyed the macroinvertebrate fauna and wet mass of naturally occurring salmon carcasses.

2. Carcass mass loss in artificial streams was initially rapid and then declined over time (k=–0.033 day–1), and no significant differences were found among natural streams.

3. Several macroinvertebrate taxa colonised carcasses, but chironomid midge (Diptera: Chironomidae) and Zapada (Plecoptera: Nemouridae) larvae were found consistently and were the most abundant (on average 95 and 2%, respectively, of the invertebrates found). Chironomid abundance and biomass increased over time, whereas Zapada abundance and biomass did not. Significant differences in abundance were found among natural streams for Baetis (Ephemeroptera: Baetidae) and Sweltsa (Plecoptera: Chloroperlidae) larvae, while no significant differences were found for chironomid and Zapada abundance or biomass.

4. Our results suggest that salmon carcasses initially undergo a high rate of mass loss that tapers off with time. Chironomid and Zapada larvae are likely to be important in mediating nutrient and energy transfer between salmon carcasses and other components of the freshwater‐riparian food web in south‐eastern Alaskan streams.