bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of temperature on advective loss of Atlantic cod (Gadus morhua) eggs from the inshore environment
Authors: Bradbury Ian R. , Snelgrove Paul V. R. , Fraser Sandra
Published: March 2003

We use a simple model of temperature‐dependent egg development and mortality to develop several hypotheses concerning the effect of temperature on the occurrence of eggs of Atlantic cod, Gadus morhua, in Placentia Bay, Newfoundland. Predictions from this exploratory model were tested through a series of synoptic ichthyoplankton surveys throughout spawning and postspawning periods during 1997 and 1998. Although several egg mortality relationships were explored through the simulation, a constant mortality rate best represented the pattern observed in the two years of data. Peaks in late stage egg densities occurred in August of both 1997 and 1998 and were apparently decoupled from egg production peaks in April. We observed a decrease in mortality and the distance dispersed during egg development with increases in water temperature. We suggest that the effects of predation are small relative to the advective effects within this system, and that the interaction between advection and temperature‐dependent vital rates of eggs may have dramatic consequences for coastal retention of propagules produced by inshore spawning events.
Congruent trends in long‐term zooplankton decline in the north‐east Atlantic and basking shark (Cetorhinus maximus) fishery catches off west Ireland
Authors: Sims David W. , Reid Philip C.
Published: March 2003

Trends in basking shark (Cetorhinus maximus) fishery catches off Achill Island, west Ireland between 1949 and 1975 were examined in relation to zooplankton (total copepod) abundance in four adjacent sea areas over a 27‐year period. The numbers of basking sharks caught and copepod abundance showed downward trends and were positively correlated (r‐value range, 0.44–0.74). A possible explanation for the downward trend in shark catches was that progressively fewer basking sharks occurred there between 1956 and 1975 because fewer copepods, their food resource, occurred near the surface off west Ireland over the same period. We suggest that the decline in basking sharks may have been due to a distributional shift of sharks to more productive areas, rather than a highly philopatric, localized stock that was over‐exploited.
Larval transport and retention of the spiny lobster, Panulirus argus, in the coastal zone of the Florida Keys, USA
Authors: Yeung Cynthia , Lee Thomas N.
Published: March 2003

The spiny lobster Panulirus argus is of ecological and commercial importance in the South Florida coast of the continental USA and throughout the Intra‐Americas Sea. Essential spiny lobster habitat in South Florida is primarily located in the Florida Keys coastal zone (including the Dry Tortugas), where the dynamic regional circulation coupled with the long planktonic larval duration (6–12 months) of P. argus raises questions of larval retention and recruitment. Locally spawned phyllosomata entrained in the Florida Current are likely to be expatriated out of the Straits of Florida, which implies that the local spiny lobster population is sustained by the transport of larval recruits from upstream locations. We examined the physical processes that may influence recruitment. Transport processes in the Keys coastal zone are spatially variable. Observed and modelled data suggest that the upper Keys is a point of onshore larval transport via the inshore meandering of the Florida Current, and the lower Keys to Dry Tortugas region apoint of retention through wind‐driven onshore/countercurrents and eddy recirculation. Eddies that propagate between the Dry Tortugas and the lower Keys facilitate the exchange of larvae between the Florida Current and the coastal zone. Northerly wind events associated with cold fronts can enhance recirculation of larvae in the upper Keys. The association of older larvae with the Florida Current front supports the hypothesis that spiny lobster larval recruits come from upstream sources in the Caribbean.
Seasonal dynamics of free and attached heterotrophic nanoflagellates in an oligomesotrophic lake
Authors: Carrias Jean‐François , Amblard Christian , Quiblier‐Lloberas Catherine , Bourdier Gilles
Published: March 2003

1. The seasonal development of heterotrophic nanoflagellates (HNF), bacteria, rotiferans and crustacean zooplankton was studied in the epilimnion of Lake Pavin, an oligomesotrophic lake in the Massif Central of France.

2. HNF abundance varied from 0.1 to 2.5 × 103 mL–1. Free‐living HNF reached their highest density in spring when the copepod Acanthodiaptomus denticornis dominated the metazooplankton. They were present in low numbers when rotifers and cladocerans were numerous.

3. Attached HNF, consisting of bicoecids and choanoflagellates, were fixed to large diatoms and to the colonial cyanobacterium Anabaena flos‐aquae. The abundance of attached HNF was significantly correlated to bacterial abundance, which fluctuated between 1.1 and 2.7 × 106 mL–1. Highest abundance of these epiphytic protists was recorded when free‐living heterotrophic nanoflagellates declined.

4. The comparison of the dynamics of heterotrophic nanoflagellates, bacteria, and the impact of zooplankton grazing suggested that prey abundance, the presence of suitable attachment sites and limited competition from the free‐living forms were the main factors controlling the development of the epiphytic flagellate protists. In contrast, the low abundance of free‐living forms during the period of rotiferan and cladoceran development suggests the prevalence of a top‐down control by predation of the metazoopankton.
The effect of two scales of habitat architecture on benthic grazing in a river
Authors: Robson Belinda J. , Barmuta Leon A.
Published: March 2003

1. This experiment studied the effects of differing levels of the complexity of substratum architecture at two spatial scales on the distribution and abundance of benthic algae and invertebrates, and the strength of the trophic interaction between invertebrate grazers and algae. Some estimates of the effects on invertebrate colonization rates were also made.

2. Four levels of microhabitat architectural complexity were created using artificial substrata (clay tiles) and placed in Mountain River, Tasmania, in two riffle types (bedrock and boulder‐cobble) of differing large‐scale substratum complexity. After a colonization period, invertebrate grazers were removed from half the tiles to measure the effects of grazing. Invertebrates on the tiles were also counted and identified. At the end of the experiment, algae were removed from the tiles and analysed for chlorophyll a.

3. Invertebrate grazers did not reduce algal biomass during the experiment, and microhabitat‐scale architecture influenced algal biomass more strongly than riffle‐scale architecture. Highly complex microhabitat architecture increased algal biomass by providing more surface area, but once standardized for surface area, algal biomass decreased as the complexity of microhabitat architecture increased.

4. Microhabitat‐scale architecture was also predominant in determining invertebrate density and the identity of the dominant grazer species. In contrast to algal biomass, invertebrate densities and species density increased with the complexity of microhabitat architecture, suggesting that refuges from flow (and possibly predation) were as important to river invertebrates as the distribution of their food source.

5. Riffle‐scale architecture had some effect on the colonization of two slow‐moving grazer taxa, but, overall, the colonization processes of slow‐moving grazers were determined mostly by the complexity of microhabitat‐scale architecture.
Long‐term recovery of a mountain stream from clear‐cut logging: the effects of forest succession on benthic invertebrate community structure
Authors: Stone Michael K. , Wallace J. Bruce
Published: March 2003

1. Changes in benthic invertebrate community structure following 16 years of forest succession after logging were examined by estimating benthic invertebrate abundance, biomass and secondary production in streams draining a forested reference and a recovering clear‐cut catchment. Benthic invertebrate abundance was three times higher, and invertebrate biomass and production were two times higher in the disturbed stream.

2. Comparison of invertebrate community abundance 1, 5 and 16 years after clear‐cutting indicated that the proportion of scrapers had decreased, whereas shredders had increased. Functional group percentage similarity indicated that the invertebrate community in the disturbed stream 16 years after clear‐cutting was more similar to the reference than to that found earlier in the disturbed stream.

3. The five indices calculated from data collected over the past 16 years, as well as the abundance, biomass and production data collected during this study, proved to be of differing value in assessing recovery of the disturbed stream from logging. Percent dominant taxon and EPT (Ephemeroptera, Plecoptera and Trichoptera) taxon richness failed to show any initial differences between reference and disturbed streams, indicating that these indices may not be useful for measuring recovery from logging. The percentage Baetis and shredder–scraper indices showed significant differences only during the 1977 study and suggest recovery (no difference between reference and disturbed) by 1982. The North Carolina Biotic Index showed continued differences during 1982 in the riffle and depositional habitats and recovery by 1993. Total macroinvertebrate abundance, biomass and production, as well as EPT abundance, indicated continued differences between the reference and disturbed streams in the 1993 study.
The effect of temperature on the response of Daphnia to toxic cyanobacteria
Authors: Claska Mary E. , Gilbert John J.
Published: March 2003

1. In a set of life‐table experiments, cohorts of neonate Daphnia pulex were exposed to a toxic strain of Anabaena affinis and A. flos‐aquae, and to a pure cyanobacterial toxin (anatoxin‐a), at 12 or 14, 19, and 25 °C. The fecundity and survival of individual animals were assessed at 1‐, 2‐ or 3‐day intervals, depending on the temperature, through to the fifth brood of the control cohort. The sensitivity of D. pulex to the cyanobacteria and the toxin at each temperature was measured by determining its finite population growth rate (λ) in an experimental treatment as a fraction of that in a control treatment. Tests with three concentrations of cyanobacteria (1.0, 2.5 and 5.0 μg mL–1) and one concentration of anatoxin‐a (1 μg mL–1), and with two clones of D. pulex, showed a consistent and statistically significant pattern of increasing sensitivity at higher temperatures.

2. Anabaena affinis affected both survivorship and fecundity, while A. flos‐aquae and its toxin, anatoxin‐a, primarily affected fecundity. Presence of cyanobacteria affected brood size, brood number, time to first reproduction and interclutch interval. Temperature affected time to first reproduction and interclutch interval at all concentrations of cyanobacteria. Brood number and brood size were little affected by temperature except at the highest concentrations of cyanobacteria. Increasing the concentration of A. flos‐aquae affected demographic parameters, especially at the lower temperatures, while increasing the concentration of A. affinis had less effect.

3. The study suggests that increasing water temperatures in natural systems should exacerbate the inhibitory effect of toxic cyanobacteria on daphniid population growth rates.
The increasing divide between First and Third Worlds: science, collaboration and conservation of Third World aquatic ecosystems
Authors: Wishart  , Davies
Published: March 2003

1. Ten of the leading journals in the field of freshwater ecology were identified using the Science Citation Index’s Journal Citation Reports. These journals were surveyed to assess the levels and patterns of collaboration in research initiatives in regions of the Third World. Membership demographics of five professional societies in this field were also examined to elucidate distribution patterns of practitioners in the field.

2. In total, 8960 papers were surveyed, of which only forty were published in a language other than English. Senior authors came from 114 of the 130 different countries listed among authors’ addresses. Of these, forty‐five were from Third World countries and sixty‐nine from the First World. Five countries were responsible for 60.64% of the papers submitted; the United States = 25.65%; Canada = 11.55%; Australia = 10.15%; the United Kingdom = 6.73%; New Zealand = 6.56%. Multi‐authored papers accounted for 73.05% of all papers.

3. Papers by authors from Third World countries accounted for only 10.93% of single‐author papers and less than 10% of multi‐authored papers. Collaboration was found in 73.05% of the papers surveyed, the vast majority of which (87.39%) was between authors from First World countries. Only 825 (9.21%) of the papers surveyed involved authors from different countries. Most of this collaboration (72.36%) was between authors from different First World countries.

4. Some 1038 papers surveyed included research undertaken in, or included authors from, Third World countries. The majority of these papers (69.08%) were submitted by authors from Third World countries, involving either multiple or single authorship. The third most common publication relating to research in Third World regions (17.4%) came from single‐author papers in which the authors were from a First World country. Only four of the papers surveyed were submitted by single authors from Third World countries working in First World countries.

5. There is a disproportionate representation of taxonomic (20.3%) and marine (10.5%) papers from the Third World regions in comparison to both lentic (8.0%) and lotic (7.4%) papers.

6. Membership demographics of the professional societies surveyed continue to reflect the historical origins of freshwater ecology. More than 80% of members in the three largest societies examined are registered in Europe and North America, while membership of the remaining societies remains largely regional.

7. It is argued that present levels of collaboration and technology transfer from the First World to the Third World are inadequate and that, given the widening gulf in terms of personnel and resources, the future of essential research on inland waters in the Third World does not bode well unless in situ capacity building within Third World countries becomes a target of First World research and funding agencies.
In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers
Authors: Thorp James H. , Delong Michael D. , Casper And Andrew F.
Published: March 2003

1.
In situ exclosure experiments in the Mississippi and Ohio Rivers determined the importance of fish predation in regulating zebra mussels (Dreissena polymorpha), an increasingly important constituent of the benthic invertebrate assemblages in both rivers.

2. We evaluated the effects of predatory fish on the density, biomass and size distribution of zebra mussels in a floodplain reach of the upper Mississippi River and in a naturally constrained reach of the Ohio River. Fifty, six‐sided, predator‐exclusion cages and fifty ‘partial’ cages (mesh at the upstream end only) were deployed, with half the cages containing willow snags and half clay tiles suspended 12–16 cm above the bottom. A single snag or tile sample unit was removed from each cage at approximately monthly intervals from July to October 1994. Types and relative abundances of molluscivorous fish were evaluated by electrofishing near the cages in both rivers. Actual and potential recruitment of young zebra mussels on to the substrata were measured using benthic samples in both rivers and estimated (Ohio River only) from counts of planktonic veligers.

3. Zebra mussels were consumed by at least three fish species in the upper Mississippi River (mostly carp, Cyprinus carpio, and redhorse suckers, Moxostoma sp.) and five species in the Ohio River (primarily smallmouth buffalo, Ictiobus bubalus, and channel catfish, Ictalurus punctatus), but potential recruitment seemed adequate to replace consumed mussels, at least in the Ohio River. The number of juvenile benthic mussels showed no apparent link with the density of veligers soon after initiation of reproduction. Recruitment of juveniles on snags and tiles was not affected by cage type (thus eliminating a potentially confounding ‘cage effect’).

4. Fish significantly influenced mussel populations, but the impact was often greatest among low density populations in the upper Mississippi. Density and biomass differed in both rivers for cage type (higher inside cages), substratum (greater on tiles), and date (increased over time). Presumed size‐selective predation was present in the Mississippi (greater on larger size classes) but was not evident in the Ohio. We hypothesize that fish in the Mississippi can more easily select larger prey from the low density populations; whereas size‐selective predation on tightly packed zebra mussels in the Ohio would be difficult.

5. Although fish can reduce numbers of Dreissena polymorpha in the two rivers, current levels of fish predation seem insufficient to regulate zebra mussel densities because of its great reproductive capacity. The recent invasion of zebra mussels, however, could lead to larger fish populations while promoting greater carbon retention and overall ecosystem secondary production.
Phytoplankton responses to experimental enhancement of grazing pressure and nutrient recycling in a small Andean lake
Authors: Queimaliños Claudia P. , Modenutti Beatriz E. , Balseiro Esteban G.
Published: March 2003

1. Three series of field experiments with different zooplankton species composition and biomass were performed in a small lake in the south Andes. We attempted to measure the responses of phytoplankton species resulting from grazing mortality and stimulation of growth by nutrient recycling.

2. Nanoflagellates contributed substantially to total phytoplankton cell abundance. Chrysochromulina parva represented 93.4%, 92.2% and 95.9% of total phytoplankton density in December, January and February, respectively. This fraction was reduced in all treatments with increasing zooplankton biomass.

3. A negative relationship was obtained between C. parva cell numbers and increase in dissolved P. On the other hand, a significant positive relationship between the abundance of the diatom Aulacoseira granulata and P concentration was observed. These results indicate that the ungrazed diatom was able to capitalise on the increase in nutrient availability.

4. As a net result of the increase or decrease of algal species we observed a change in the nano:net phytoplankton relationship. The outcome of three‐day incubations with increased zooplankton biomass was an increasing importance of net phytoplankton.

5. The results indicate the importance of the indirect effects of zooplankton (through nutrient recycling) in the increase in diatoms, and the role of grazing as a growth‐limiting factor for the flagellate C. parva.
Effects of woody debris on the habitat of juvenile masu salmon (Oncorhynchus masou) in northern Japanese streams
Authors: Inoue Mikio , Nakano Shigeru
Published: March 2003

1. The effects of woody debris on stream habitat of juvenile masu salmon (Oncorhynchus masou) were examined at two spatial scales, stream reach and channel unit, for first‐ to third‐order tributaries of the Teshio River in northern Hokkaido, Japan. The forty‐eight study reaches were classified into three distinct types: coarse‐substrate step‐pool (CSP), coarse‐substrate pool–riffle (CPR) and fine‐substrate pool–riffle (FPR) reaches. Each reach type included reaches with different riparian settings, broadly classified as forest (relatively undisturbed forest and secondary forest after fires) or grassland (bamboo bushland and pasture).

2. The reach‐scale analyses showed that neither total pool volume nor pool‐to‐pool spacing was correlated with woody debris abundance in any of the three reach types. Masu salmon density was positively correlated with both woody‐debris cover area and total cover area, but not with total pool volume in the reaches.

3. Channel‐unit‐scale analyses revealed that woody debris reduced non‐pool velocity, increased pool depth and retained fine sediment in pools in FPR reaches, where the size of woody debris was very large relative to the substrate material size. However, woody debris did not influence any of the hydraulic variables (depth, velocity, substrate) in either non‐pools or pools of CSP and CPR reaches. Habitat use by masu salmon in non‐pools or pools was affected by woody‐debris cover area or total cover area rather than by hydraulic variables in any of the reach types.

4. The effects of woody debris on habitat at the reach‐ and channel‐unit scales in the study area were less than those indicated by previous work in the Pacific Northwest, North America, owing to the relatively small size of the riparian trees. However, the overall results suggested that woody debris in the study area contributed to masu salmon habitat by providing cover at the smaller, microhabitat scale.
Production potential of aquatic plants in systems mixing floating and submerged macrophytes
Authors: Forchhammer Nina Cedergreen
Published: March 2003

1. To investigate whether the areal production of aquatic plant systems can be increased by growing floating and submerged plants together, the floating fern Azolla filiculoides was grown at six densities and two nutrient availabilities in the presence and absence of the submerged macrophyte Elodea canadensis.

2. High nutrient availability did not affect the total areal biomass production, but raised the internal N concentration of Azolla and Elodea by 34% and 152%, respectively, and the internal P concentration by 50% and 378%.

3. High Azolla density reduced Elodea production, whereas Elodea did not affect the production of Azolla. A maximal total production of 4.0 g DW m−2 day−1 was obtained at an Azolla density at and above full surface cover, when Elodea contribute with less than 10% to the total. This contribution did not raise the combined production of Azolla and Elodea significantly above the production of Azolla grown alone. Thus, maximum production was not enhanced by growing floating and submerged macrophytes together.
Associations between stream fish and benthos across environmental gradients in southern Ontario, Canada
Authors: Kilgour Bruce W. , Barton David R.
Published: March 2003

1. The relationship between fish and benthic invertebrate communities in wadeable streams in southern Ontario, Canada, was examined using three independent and spatially distinct data sets.

2. Associations between fish and benthos were always significant when benthos were identified to family and often at the level of phylum. Identification to genus improved the strength of the fish–benthos association in one case. In contrast, identification to species did not improve the strength of the fish–benthos association. Associations between benthos and fish were weaker for one study utilizing a ‘rapid’ bio‐assessment protocol involving field sorting and identification, and a second study which utilized winter benthic collections.

3. In two surveys, stream temperatures were important to the distributions of both fish and benthos, while in a third survey, fish and benthos were primarily influenced by stream size. In all three studies, fish and benthos were associated with similar suites of environmental variables, suggesting that the fish–benthos associations in these streams was driven by corresponding environmental tolerances.

4. Although there was significant variation in the strength of the fish–benthos association which could be attributed to differences in sampling methodologies, the findings from the present study confirm that stream fish and benthos are significantly associated. Therefore, surveys of benthos can be used to make inferences on the condition of fish community composition.
Large‐scale assessments of river health using an Index of Biotic Integrity with low‐diversity fish communities
Authors: Harris J. H. , Silveira R.
Published: March 2003

1. Effective tools are needed to measure the ‘health’ of rivers at scales large enough to be useful for management. Indicators for assessing the complex of variables that constitutes river health need to be ecologically based, efficient, rapid and consistently applicable in different ecological regions.

2. A large‐scale survey of rivers in New South Wales, Australia provided data to test the Index of Biotic Integrity (IBI). The IBI employs the fish‐community attributes, identified using regional and river‐size data, expected for a river reach of excellent environmental quality. It uses metrics based on species richness, abundance, community structure and the health of individual fish. IBI metrics were established to suit a relatively low‐diversity and unspecialized freshwater fish fauna in south‐eastern Australia, totalling 55 species.

3. The IBI was able to discriminate between relative levels of environmental quality within a diverse set of stream systems and four presumptive ecological regions. The index was validated by testing the repeatability of scores, and by comparison of IBI scores at eighty sites with an independent measure of potential catchment condition, the River Disturbance Index.

4. Assessments of metric performance showed that eleven of the twelve metrics contributed satisfactorily. One metric based on trophic guild performed poorly and should be deleted from the index. Six other recommendations are made to enhance the performance of the IBI.

5. Results show that, while all large rivers have been disturbed, rivers in the Murray region and those in many coastal montane areas are particularly degraded.

6. The IBI results presented here demonstrate a validated method for large‐scale monitoring of river health based on a fish fauna of limited diversity, in the absence of suitable reference sites.
Aerial survey of waterbirds on wetlands as a measure of river and floodplain health
Authors: Kingsford R. T.
Published: March 2003

1. This study highlights the use of waterbird communities as potential measures of river and floodplain health at a landscape scale.

2. The abundance and diversity of a waterbird community (54 species) was measured over 15 trips with four aerial and three ground counts per trip on a 300‐ha lake in arid Australia.

3. Aerial survey estimates of individual species were significantly less precise (SE/mean) than ground counts across two (11–100 and > 1000) out of four abundance classes of waterbirds: 0–10, 11–100, 101–1000 and > 1000. Standard error/mean as a percentage decreased with increasing abundance from about 60% for the lowest abundance class to 18% for the largest abundance class.

4. Aerial survey estimates were negatively biased for species in numbers of less than 10 and greater than 5000 but unbiased compared to ground counts for other abundance classes. Aerial surveys underestimated numbers of waterbirds by 50% when there were 40 000 waterbirds. Three ground counts found about seven more waterbird species than four aerial surveys. One ground count took about 150 times longer than two aerial surveys and cost 14 times more.

5. Regression models were derived, comparing aerial survey estimates to ground counts for 31 of 36 species for which there were sufficient data. Aerial survey estimates were unbiased for most of these species (67%), negatively biased for six species and positively biased for one species. Estimates were negatively biased in species that occurred in small numbers or that dived in response to the aircraft.

6. River system health encompasses the state of floodplain wetlands. Waterbirds on an entire wetland or floodplain may be estimated by aerial survey of waterbirds; this is a coarse but effective measure of waterbird abundance. Aerial survey is considerably less costly than ground survey and potentially provides a method for measuring river and floodplain health over long periods of time at the same scale as river management.
Continuing dispersal of freshwater triclads (Platyhelminthes; Turbellaria) in Britain with particular reference to lakes
Authors: Young J. O. , Reynoldson T. B.
Published: March 2003

1. A survey of lakes in Anglesey and Snowdonia, Wales, in the summer of 1997 recorded changes in the triclad fauna which had occurred since earlier studies in the 1950s and in 1973. Two native species, Polycelis tenuis and Dugesia polychroa, and two immigrants, Planaria torva and especially Dugesia tigrina, have increased their range. The triclad fauna has remained unchanged with time in eleven out of sixteen lakes in Snowdonia, in contrast to only one out of fourteen lakes on Anglesey. This supports the hypothesis produced in the 1950s, that the triclad fauna of the ion‐poor, unproductive lakes in Snowdonia would change little with time, being maintained by ecological interactions, whereas the ion‐rich, productive lakes on Anglesey, from which native Dugesia spp. and Dendrocoelum lacteum are historically absent, would increase in triclad diversity.

2. An examination of national records for the distribution of D. tigrina and Pl. torva indicated their continuing dispersal in both still and running waters in mainland Britain, with the former species having the greater frequency of occurrence.

3. The reasons for this may be that D. tigrina is (a) more easily dispersed, (b) a more opportunistic, catholic feeder, (c) a more vigorous competitor, (d) able to reproduce asexually and (e) able to prey to some extent on other triclad species, as shown in the laboratory but not yet confirmed in the field. The absence of D. tigrina and Pl. torva from unproductive lakes may be explained in terms of low temperature and feeding mode, and a low standing crop of gastropods, respectively.

4. Seven surveys (1961–1997) of the triclad fauna (six species) of Colemere, England, revealed that D. tigrina was confined to one small area of the littoral zone until the mid‐1980s, after which it spread fairly rapidly to occupy the entire shore by 1997. Its expansion has been to the detriment of all the native species, particularly P. tenuis, except Dd. lacteum. The possible extinction of Pl. torva may be linked to a numerical reduction in snails, particularly Potamopyrgus jenkinsi.

5. Dugesia tigrina has an adverse effect on the native triclad fauna in lakes, particularly when only a few species are present. This has been explained in terms of the availability of a wider variety of food. The presence of a larger number of triclad species denies the immigrant food items, particularly crustaceans and snails, the food refuges of Dd. lacteum and Dugesia spp., respectively. However, the long‐term study of Colemere has shown that more diverse triclad faunas may also be vulnerable to this immigrant. The effect of Pl. torva on native triclads remains uncertain.
Influence of spring warming on the predation rate of underyearling fish on Daphnia– a deterministic simulation approach
Authors: Mehner Thomas
Published: March 2003

1. According to previous field studies in the biomanipulated Bautzen reservoir (Germany), a midsummer decline of the dominating zooplankter, Daphnia galeata, was suggested to be initiated by a simultaneous occurrence of low fecundity of the daphnids and a selective feeding of underyearling fish on mature daphnids. The timing of both processes was assumed to be triggered by spring water temperature. However, the field data were not appropriate for testing whether yearly differences in spring warming are strong enough to control the predation rate of underyearling fish on daphnids.  2. By combining field data on fish growth, feeding and population mortality, the daily uptake of Daphnia by a virtual population of underyearling perch (Perca fluviatilis) was simulated. In addition, the daily predatory mortality of mature daphnids was calculated independently. Scenarios with a warm and a cold spring were compared. Furthermore, the delayed warming of a pelagic zone of a lake versus a littoral one was simulated. Sensitivity of the simulation to changes in five parameters was tested.  3. In both the warm spring scenario and the littoral warming scenario, more daphnids in general and more mature daphnids in particular were eaten, compared with the cold spring and pelagic scenarios. The predatory mortality of mature daphnids was driven by the increasing gape size of growing fish such that in warmer years the fish reach earlier the size at which they can eat mature daphnids.  4. The simulation was most sensitive to changes in daily mortality rate of the fish and to the size at maturity of the daphnids. Since at least the fish mortality is also temperature‐dependent via the growth rates of fish, the predation rate of perch on D. galeata in Bautzen reservoir is substantially increased during a warm spring. This underlines the assumption that even a slight global warming may have a decisive influence on food web processes due to the fine‐scaled patterns of trophic interactions in lakes.
Effects of the benthic suspension feeder Dreissena polymorpha on zooplankton in a large river
Authors: Jack Jeffrey D. , Thorp James H.
Published: March 2003

1. We conducted a series of in situ enclosure experiments to assess the impact of zebra mussels (Dreissena polymorpha) on the plankton of the Ohio River. Adult mussels were suspended in pelagic enclosures (‘potamocorrals’) at three densities (0, 1000, 2500 mussels per corral) and incubated for 6 days with daily plankton and physiochemical sampling.  2. The presence of adult zebra mussels was correlated with a shift in composition of the phytoplankton community and a severe reduction in some rotifers. The effects of zebra mussels on the larger zooplankton were taxon‐dependent, but bacterial density showed no trend among treatments.  3. Zebra mussels may have significant negative impacts on zooplankton, which may in turn alter riverine food webs.
Macroinvertebrate community structure along gradients of hydraulic and sedimentary conditions in a large gravel‐bed river
Authors: Rempel Laura L. , Richardson John S. , Healey Michael C.
Published: March 2003

1. The spatial distribution of macroinvertebrate species was examined in relation to hydraulic and sedimentary conditions in a large gravel‐bed river, the Fraser River, Canada. Mean annual discharge in the Fraser River is 2900 m3 s−1 and annual flood discharge, due to snowmelt in May and June, averages 8760 m3 s−1.  2. Invertebrates were sampled from four water depths (0.2, 0.5, 1.5, 3.0 m) at various levels of discharge that together captured the spatial and temporal variability of the physical habitat. Several hydraulic (near‐bed shear velocity, Boundary Reynolds number, turbulence intensity, depth‐averaged velocity, Froude number, Reynolds number) and substratum variables (mean grain size, Trask's sorting coefficient, Nikuradse's roughness, percentage of fine sediment, and Shields entrainment function) were measured for each sample of macroinvertebrates. Concentrations of fine and coarse particulate organic matter were also assessed.  3. The physical habitat was characterized by a major gradient of hydraulic conditions that corresponded positively with increasing water depth and accounted for 52% of the total variation in the habitat data. Substratum conditions and the concentration of organic matter explained 24% of the total variation in the habitat data.  4. The distribution of invertebrates was correlated significantly with hydraulic variables and suggests that hydraulic conditions represent a major physical gradient along which the benthic community is organized. The distribution of organic matter and substratum texture were also important for some species. The spatial distribution of most species reflected morphological and trophic suitability to particular habitat conditions.  5. Hydraulic stress associated with foraging and maintaining position, as well as organic matter retention in coarse substrata, are probable mechanisms affecting the spatial distribution of macroinvertebrates.
Effects of aquatic plant management on stream metabolism and oxygen balance in streams
Authors: Kaenel Barbara R. , Buehrer Heinrich , Uehlinger Urs
Published: March 2003

1. In unshaded, nutrient‐rich streams, prolific growth of stream macrophytes often results in flows that over‐top the banks and in high primary production and respiration that may result in extreme diel variations in dissolved oxygen. Consequently, water protection authorities commonly remove macrophytes periodically.  2. We investigated the effect of plant removal on stream metabolism and oxygen balance in two Swiss streams with a high macrophyte biomass. We monitored the concentration of dissolved oxygen before and after macrophytes were removed by cutting and dredging, and calculated rates of gross primary production and ecosystem respiration by means of diel oxygen curves.  3. The removal of plants, which had reached a dry biomass of 320–420 g m−2 immediately before plant removal, had a different impact on stream metabolism in the two streams. In the first (plants removed in May), neither primary production nor ecosystem respiration were significantly affected. In the second (plants removed in late July), gross primary production and ecosystem respiration were reduced by about 70%. In this latter stream gross primary production increased in the first 2 weeks after plant removal but never recovered to pre‐disturbance levels.  4. The removal of plants coincided with only a moderate increase in nocturnal oxygen concentration (+1 mg L−1). This, and the rapid partial recovery of stream metabolism in the second stream, suggests that an increase in the oxygen concentration after plant cutting is transient in unshaded, nutrient‐rich streams.
The impact of regional‐scale changes in the weather on the long‐term dynamics of Eudiaptomus and Daphnia in Esthwaite Water, Cumbria
Authors: George D. G.
Published: March 2003

1. Year‐to‐year changes in the weather have a profound effect on the seasonal dynamics of zooplankton in lakes. Here, I analyse some zooplankton data from Esthwaite Water in Cumbria and demonstrate that much of the recorded inter‐annual variation can be related to regional‐scale changes in the weather.  2. The first data set analysed shows the effect of changes in the water temperature on the winter abundance of the calanoid copepod Eudiaptomus gracilis. The highest numbers of Eudiaptomus were recorded when the winters were mild and the lowest when the winters were cold.  3. Winter temperatures in northern and western Europe are now known to be influenced by the atmospheric feature known as the North Atlantic Oscillation (NAO). Positive values of the NAO are associated with mild winters and westerly winds and there was a significant positive correlation between the winter abundance of Eudiaptomus in Esthwaite Water and this empirical index of change.  4. The second data set analysed shows the effect of wind‐induced mixing on the summer abundance of Daphnia. The highest numbers of Daphnia were recorded in years when the early summer thermocline was deep and the lowest number in years when the thermocline was shallow.  5. One of the most important factors influencing the depth of the early summer thermocline in the English lakes is the position of the north‐wall of the Gulf Stream. Southerly movements of the Gulf Stream are typically associated with higher winds, whilst northerly movements are associated with stable conditions. In Esthwaite Water, a significant positive correlation was recorded between the abundance of Daphnia and the depth of the early summer thermocline and significant negative correlations between the same variables and the position of the Gulf Stream.  6. A detailed analysis of the seasonal variations recorded in one calm and one windy year suggest that the main factor responsible for these correlations was the entrainment of nutrients which then stimulated the growth of edible algae. Daphnia numbers were low in 1968 (a ‘north’ Gulf Stream year which was relatively calm) and high in 1972 (a ‘south’ Gulf Stream year with intense wind‐mixing).
Refractory dissolved organic matter can influence the reproduction of Caenorhabditis elegans (Nematoda)
Authors: Höss Sebastian , Bergtold Matthias , Haitzer Markus , Traunspurger Walter , Steinberg Christian E.W.
Published: March 2003

1. We investigated the effect of refractory dissolved organic matter (refractory DOM: fulvic acids (FAs) and ultrafiltrates (UFs)), isolated from five different sources, on the reproduction of the bacterivorous nematode Caenorhabditis elegans. Nematodes were exposed to DOM (0.5–64 mg L−1 dissolved organic carbon) during a whole life cycle (72 h). At the end of the test, the number of offspring per worm was determined.  2. We also studied the effect of refractory DOM on abundance, cell size, and activity of the bacteria (Escherichia coli) that were used as a food source for the nematodes, to assess possible indirect effects of DOM via the food organisms.  3. The effects of DOM on the reproduction of C. elegans varied, depending on the origin and concentration of DOM. FAs isolated from a soil leachate and from the effluent of a waste water plant, as well as UFs from a humic lake and from a marsh, stimulated the reproduction of C. elegans. FAs from ground water had no effect, while FAs from a humic lake inhibited the reproduction of the nematodes. All effects occurred at ecologically relevant DOM concentrations and showed clear dose–response relationships.  4. Neither bacterial abundance nor cell size were influenced by refractory DOM. Bacterial activity was unaffected by four types of DOM. Only FAs from the humic lake caused a significant decrease in bacterial activity over 72 h.  5. The negative effect of FAs from the humic lake on nematode reproduction may be a consequence of a lower bacterial activity in this treatment. The positive effects of refractory DOM, however, could not be related to bacterial parameters. Therefore, we assume that the DOM directly influenced the reproduction of C. elegans. We speculate that refractory DOM can potentially be an additional carbon source or a source of trace nutrients influencing the reproduction of C. elegans. Adsorption of refractory DOM on bacterial cells, serving as food for the nematodes, may have been an important factor for the availability of DOM for C. elegans.
Historical changes in species composition and richness accompanying perturbation and eutrophication of Danish lowland streams over 100 years
Authors: Riis Tenna , Sand‐Jensen Kaj
Published: March 2003

1. European lowland streams have experienced increased perturbation and eutrophication during the past 100 years. We use archive information from 27 Danish stream sites around 1896 and new data from 208 stream sites in 1996 to evaluate the accompanying changes in stream vegetation. Among the stream sites, 13 were both studied in 1896 and 1996.  2. The species richness of submerged plants has declined profoundly over the 100‐year period, particularly among the large group of Potamogeton species. This is evident both from the direct comparison of the 13 stream reaches included in both studies, and from the general comparison of all stream reaches included in the two studies.  3. The Potamogeton vegetation has become less diverse, and is now dominated by species resistant to frequent disturbance through a high dispersal capacity. Potamogeton species, adapted to eutrophic conditions, have also increased relative to species more typical of oligotrophic conditions over this period. The dominant submerged species in the contemporary stream vegetation generally show a high capacity for dispersal and regrowth of detached shoots.  4. The decline of species richness in Danish streams can be partly explained by a decline in the species richness in lakes in the stream system. The rich vegetation observed downstream of lakes in the past has mostly disappeared due to loss of the vegetation in the now eutrophic lakes and increasing turbidity downstream.  5. The overall decline in richness, and the directional change in dominance patterns among stream species, can thus be explained by the loss of suitable habitats and the strong anthropogenic impacts, which have driven several European aquatic species close to extinction.
Effects of urbanization on streams of the Melbourne region, Victoria, Australia. II. Benthic diatom communities
Authors: Sonneman Jason A. , Walsh Christopher J. , Breen Peter F. , Sharpe Andrew K.
Published: March 2003

1. Epilithic and epiphytic diatom community composition were assessed in small streams of the Melbourne region to test the effects of (a) urban density (sub‐catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).

2. Communities separated into three groups: eastern hinterland, western hinterland and a metropolitan group. Separation of eastern and western hinterland groups, and of eastern and western sites within the metropolitan group were best explained by patterns of electrical conductivity, basalt geology and annual rainfall. Separation of metropolitan and hinterland groups, and patterns within the hinterland groups were best explained by nutrient gradients (phosphorus, ammonia and total nitrogen).

3. Nutrient concentrations were not only apparently influenced by urban density but also by effluents from small sewage treatment plants and agricultural activities at a few sites.

4. Species richness did not vary consistently between the metropolitan and hinterland groups but within the western hinterland, sites with low nutrient concentrations tended to be more species‐rich than mildly enriched sites.

5. Composition of both diatom and macroinvertebrate communities (assessed in a concurrent study) were sensitive indicators of urban‐derived impacts. However, diatoms were better indicators of nutrient enrichment, while macroinvertebrates were better integrative indicators of catchment disturbance.
The impact of an introduced bivalve (Corbicula fluminea) on the benthos of a sandy stream
Authors: Hakenkamp Christine C. , Ribblett Suzanna G. , Palmer Margaret A. , Swan Christopher M. , Reid Janet W. , Goodison Mike R.
Published: March 2003

1. The effect of an exotic, burrowing bivalve (Corbicula fluminea) on the benthic fauna of a sandy‐bottomed stream was assessed by field and laboratory experiments. Corbicula differs from other freshwater, non‐native bivalves in that it both filter‐ and pedal‐feeds and thus has the potential to influence the streambed community in different ways.

2. In the field, cages were used to vary the abundance of Corbicula in the streambed. Increasing abundance of Corbicula was negatively associated with the abundance of benthic bacteria and flagellates but had no apparent effect on other protists or meiofauna.

3. In the laboratory, we compared the effect of Corbicula on the benthic community when the bivalves were able both to filter‐ and pedal‐feed with that when they were able only to filter‐feed. Bivalves restricted to filter‐feeding were placed in sediment lacking benthic fauna and organic matter, then the benthos in nearby natural sediment was compared with the community present when Corbicula was able to move freely through the sediment and both to filter‐ and pedal‐feed. Corbicula able to pedal‐feed were again associated with a decreased abundance of benthic flagellates and bacteria, as well as diatoms.