bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐annual external annuli in the freshwater musselsAnodonta grandis grandisandLampsilis radiata siliquoidea*
Authors: DOWNING WILLIAM L. , SHOSTELL JOSEPH , DOWNING JOHN A.
Published: May 2006

1. Two species of freshwater mussels,Lampsilis radiata siliquoideaandAnodonta grandis grandiswere measured and permanently marked with pointed, plastic tape positioned at the postero‐lateral edge of the shell. Mussels were returned to original conditions at two sites in an oligotrophic lake, retrieved at yearly intervals, re‐measured, and external annuli that had been added since marking were counted.

2. External annuli were formed much less frequently than annually; the overall median number of annuli formed each year was 0.5. In one of the four populations studied, the rate of annulus formation was >1 in small animals and <1 in large ones. Many mussels showed no new external annuli at all, even several years after marking.

3. Ford‐Walford plots of shell annuli did not yield consistent indices of shell growth. Repeated measurement of mussels in successive years showed that estimates of growth based on shell annuli consistently overestimated real shell growth.
Ecology of invertebrate predators in a Coastal Plain stream
Authors: SMITH LANE C. , SMOCK LEONARD A.
Published: May 2006

1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand‐bottomed, headwater stream in Virginia, U.S.A.

2. Annual mean density and biomass of predators in debris dams were 3897 individuals m−2 and 2.5 g dry mass m−2, respectively, but only 711 individuals m−2 and 0.2 gm−2 on the sediment. Predator production was 8.36 gm−2yr−1 in debris dams compared to 1.52 gm−2yr−1 on the sediment. Annual predator production, weighted by habitat availability, was 1.73gm−2yr−1.

3. The predominant taxa in terms of production were the chironomids Thienemannimyia spp, complex, Ablabesmyia parajanta, Zavrelimyia sp., and the odonate Cordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild.

4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 gm−2yr−1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the channel surface of the stream.
Limiting nutrients for periphyton growth in sub‐alpine, forest, agricultural and urban streams
Authors: CHESSMAN BRUCE C. , HUTTON PRIMROSE E. , BURCH JOANNE M.
Published: May 2006

1. Nutrient‐diffusing artificial substrata were used in summer and autumn to assess limiting nutrients for periphytic algal growth in streams draining sub‐alpine, forested, agricultural and urban catchments in eastern Victoria, Australia.

2. Chlorophyll a density was primarily limited by nitrogen in most cases; often phosphorus was secondarily limiting. One sub‐alpine, one forest and one agricultural stream were primarily phosphorus limited in at least one season. Added trace elements and vitamins did not increase chlorophyll density.

3. The dominant filamentous algal genera did not differ greatly between various nutrient enrichments. However, the relative abundance of Stigeodanium spp. was sometimes increased on substrata containing the limiting nutrient.

4. The results suggest that nutrient limitation is a widespread phenomenon in Victorian streams, and that limiting nutrients can be inferred from stream‐water nitrogen to phosphorus ratios in many instances.
Susceptibilities of different‐sized ciliates to direct suppression by small and large cladocerans
Authors: JACK JEFFREY D. , GILBERT JOHN J.
Published: May 2006

Laboratory experiments compared the susceptibilities of six ciliates and the rotifer Keratella cochlearis to predation and interference from Daphnia pulex and Bosmina longirostris.

 Susceptibilities of the ciliates to D. pulex were similar to or less than that of the rotifer, and decreased with increasing ciliate size. Most ciliates were just as susceptible to

B. longirostris as to the much larger D. pulex. The jumping response of the oligotrich Strobilidium gyrans appeared to be an effective defence against B. longirostris.

 Clearance rates of B. longirostris and D. pulex on different ciliate species at a density of 1,3 ciliates ml−1 ranged from 1–30 to 5–24ml ind.−1 day−1, respectively. In natural plankton communities, cladocerans could impose high mortality rates on ciliates and shift the size structure of ciliate assemblages towards larger and less susceptible species.
Effects of a forest disturbance on shredder production in southern Appalachian headwater streams
Authors: STOUT BEN M. , BENFIELD E.F. , WEBSTER J.R.
Published: May 2006

The effects of a forest disturbance were investigated by comparing production of leaf‐shredding aquatic insects in three streams draining a mature hardwood forest and three streams draining an 11‐year‐old, cable‐logged clearcut.

 Reference streams contained significantly greater mean annual standing crop of leaf material and significantly more slow‐processing leaf material than disturbed streams. Disturbed streams had a significantly higher mean annual standing crop of fast‐processing leaf material than the reference streams.

 Leaf‐shredding cranefly (Tipula abdominalis), caddisfly (Pycnopsyche gentilis), and stonefly (Tallaperla maria) larvae comprised over 95% of shredder biomass in all streams. Total shredder production was significantly greater (P<0.05) in disturbed versus reference streams, but individual production rates were not significantly different between stream types.

 Pycnopsyche gentilis larvae were present at higher densities and achieved significantly greater annual biomass in disturbed versus references streams, Biomass of P. gentilis was significantly correlated with the standing crop of fast‐processing, early successional leaf material in samples, whereas biomass of other shredders was correlated significantly with medium or slow‐processing leaf species characteristic of later stages of forest succession.
Exploration and rehabilitation of hydraulic habitats in streams using principles of fluvial behaviour
Authors: NEWBURY ROBERT , GABOURY MARC
Published: May 2006

The combination of elements from geomorphology, open‐channel hydraulics, and hydraulic habitat requirements of stream fish forms the basis for an ecologically sound ‘soft engineering’ of river channels.

 Interpreting and mapping the hydraulic geometry of streams and locally varied flow conditions can be accomplished with plane table surveys and customized field‐data sheets. This information can serve to manage hydraulic habitats preferred by fish.

 The use of fluvial characteristics to design preferred hydraulic habitats is illustrated in two examples: (i) a walleye (Stizostedion vitreum vitreum Mitchill) spawning rehabilitation project undertaken in a stream channelized as a lowland drainage canal, and (ii) a trout (Salvelinus fontinalis Mitchill and Oncorhynchus mykiss Walbaum) habitat‐enhancement project to create additional holding and resting areas for adult fish in a stream paved with glacially deposited boulders modified by a road crossing.

 In both examples the ‘soft engineering’ of the river channels enhanced the hydraulic fish habitat.
Riparian vegetated buffer strips in water‐quality restoration and stream management
Authors: OSBORNE LEWIS L. , KOVACIC DAVID A.
Published: May 2006

A review is presented of the literature on riparian vegetated buffer strips (VBS) for use in stream‐water‐quality restoration and limitations associated with their use are discussed. The results are also presented of recent investigations on the effectiveness of a forested and a grass vegetated buffer strip for reducing shallow subsurface inputs of nutrients from agriculture to a stream in central Illinois, U.S.A.

 Because riparian zones link the stream with its terrestrial catchment, they can modify, incorporate, dilute, or concentrate substances before they enter a lotic system. In small to mid‐size streams forested riparian zones can moderate temperatures, reduce sediment inputs, provide important sources of organic matter, and stabilize stream banks.

 Several questions on the utility and efficiency of vegetated buffer strips for stream restoration still remain unanswered, including: what types (grassvforest) are most efficient; do they become nutrient saturated; are they only temporary sinks; how does species composition influence effectiveness; and, what is the optimal width of buffer to facilitate nutrient reduction under different conditions?

 Water samples were collected (1989–90) from lysimeters located at three depths (60, 120, and > 120cm) in an upland area planted in conventional row crops (corn and soybean) and in three adjacent riparian buffer treatments, a 39m wide grass buffer. a 16 m wide mature forested buffer, and a buffer planted in row‐crops to the stream bank. Concentrations of dissolved and total phosphorus and nitrate‐N in each sample were determined following major precipitation events over a seventeen month period.

 Both the forested and grass VBS reduced nitrate‐N concentrations in shallow groundwater (up to 90% reduction). On an annual basis the forested VBS was more effective at reducing concentrations of nitrate‐N than was the grass VBS, but was less efficient at retaining total and dissolved P.

 During the dormant season, both grass and forested buffer strips released dissolved and total P to the groundwater. The VBS apparently acted as a nutrient sink for much of the year, but also released accumulated nutrients during the remaining portion of the year. Periodic harvesting of plant biomass may reduce the amount of P released during the dormant season.

 VBSs are not as effective in agriculture areas with tile drained fields. Alternative restoration practices such as discharging drain tiles into wetlands constructed parallel to the stream channel may prove to be a more effective means of controlling non‐point‐source agricultural inputs of nutrients in such areas.
Identification of predominant environmental factors structuring stream macroinvertebrate communities within a large agricultural catchment
Authors: RICHARDS CARL , HOST GEORGE E. , ARTHUR JOHN W.
Published: May 2006

Patterns of macroinvertebrate community composition were examined in streams within a 40000‐km2 catchment in central Michigan, U.S.A., to identify the major environmental gradients influencing community variation. Agriculture and associated clay and sandy soils predominated in much of the region.

 Eighty macroinvertebrate taxa were collected from stream surveys conducted during May and August 1990. Community composition varied primarily by the proportions of Plecoptera and Ephemeroptera. Benthic communities from the heaviest agricultural zones were most different from those at other sites.

 Chemical composition among the sites varied most in relation to nutrients (NH3, NO3, PO4). Other parameters were relatively similar. Physical characteristics of the sites were scored in six habitat categories: (i) substrate characteristics, (ii) instream cover, (iii) channel morphology, (iv) riparian zone and stream‐bank conditions, (v) riffle/run quality, (vi) pool quality. Most physical habitat scores were lowest in the intense agriculture zones.

 The relative importance of physical and chemical variables in explaining variation in macroinvertebrate communities was quantified using canonical correspondence analysis. Substrate characteristics were most important in both surveys. Significant correlations (P<0.05 and P<0.10) were observed between substrate quality and total numbers of Ephemeropteran, Plecopteran, and Trichopteran taxa. These relationships reflected correlations from sites in the clay soil‐type region (P<0.01 and P<0.10) which contrasted with non‐significant results from the less impacted, sandy soil‐type region.

 Effective stream restoration efforts in this region will require the alteration of local land‐use activities that influence the physical habitat. Further development of empirical relationships between catchment activities and substrate and channel characteristics within natural geomorphic regions is essential for the evaluation of restoration projects.
Reproduction in two submersed macrophytes declines progressively at low pH
Authors: TITUS JOHN E. , HOOVER DAVID T.
Published: May 2006

Greenhouse experiments tested the effect of pH 5 v pH 7.5 on reproductive success for the freshwater macrophytes Najas flexilis, an annual, and Vallisneria americana, which perennates as a tuber.

 Seed production by the small Najas plants grown at pH 5 averaged 0.25 seeds/plant, in contrast to 95.5 seeds/plant at pH 7.5. At low pH, Vallisneria grown from seeds produced no flowers and too few tubers to replace themselves, so that sexual reproduction failed nearly completely for both species.

  Vallisneria grown from tubers produced 97% less total tuber mass at pH 5 (0.4 v 14.9 g), the compounded result of producing, on average, 89% fewer and 82% smaller tubers. The smaller tubers developed at pH 5 were less likely to overwinter in the field, and those surviving tubers subsequently grew into smaller plants.

 These findings generated the hypothesis of a closing spiral: growth at low pH (and relatively low CO2 concentrations) results in small plants that produce a smaller number of progressively smaller tubers each autumn, which in turn develop into progressively smaller plants each summer. This hypothesis was supported by field transplant experiments in two acidic Adirondack Mountain (NY) lakes.
Spatial variation in the distribution of stream invertebrates: implications of patchiness for models of community organization
Authors: DOWNES BARBARA J. , LAKE P.S. , SCHREIBER E.S.G.
Published: May 2006

Variation in abundances of stream fauna across a range of spatial scales has been neglected, yet such variation can have important implications for experimental and descriptive work. We tested the hypothesis that the abundances of stream animals living on stones vary between sites within the same stream order, riffles within the same site and groups of stones within the same riffle. We also examined how epilithon and water depth and velocity varied over these spatial scales.

 Thirty stones were sampled from each of three sites in a fourth‐order section of the Taggerty and Steavenson Rivers, south‐eastern Australia. At each site, fifteen stones were taken from each of two riffles; within each riffle, the fifteen stones were collected as five groups of three stones within 0.5m of each other. For each stone, we measured water depth and velocity, took samples of epilithon to estimate chlorophyll a concentrations, organic biomass and bacterial and algal cell densities, and collected all macroinvertebrates.

 Hierarchical analyses of variance revealed that species richness did not vary over any of the spatial scales, but densities of individuals varied substantially between riffles and groups of stones. Of the thirty‐five most abundant taxa, three‐quarters (twenty‐seven) varied over one or more of the spatial scales, with variation between riffles being particularly common. DECORANA analyses confirmed that two of the three sites had riffle faunas that were dissimilar to each other, whereas the third site had riffle faunas that were very similar. Significant spatial variation was observed also in water velocities and depths and chlorophyll a and organic biomass concentrations.

 Overall, we have demonstrated that significant variation in faunal densities may occur over small spatial scales, such as those represented by groups of stones. Moreover, such variation was not consistent between taxonomically or functionally related species within the assemblage.

 The results emphasize the need for stream ecologists to be aware of the ramifications of such variation. Neglect of small‐scale variation has produced spatially confounded designs in both surveys and experimental studies. Additionally, the assumption that variation over small scales does not occur or is trivial seems to have been responsible for the virtual enshrinement of certain large‐scale models of community organization.
Macroinvertebrate communities in streams in the Himalaya, Nepal
Authors: RUNDLE SIMON D. , JENKINS ALAN , ORMEROD S.J.
Published: May 2006

Macroinvertebrates were sampled in the riffles of fifty‐eight streams from three regions of the Himalaya (Anapurna, Langtang and Everest) in Nepal. A semi‐quantitative method with identification to family level was used to describe communities on‐site.

 Stream physicochemistry was assessed and the community structure of macroinvertebrates was related to chemistry, physiography (substratum composition, altitude and size), geographical location and the dominant land use in each catchment (terraced agriculture, forest or scrub). Community data were analysed by ordination (DECORANA) and classification (TWINSPAN).

 The concentration of cations in stream water decreased significantly with altitude. Chemistry also differed between regions; sites from Anapurna had a higher pH and conductivity than those in the other two areas.

 Communities were dominated by aquatic insect larvae, with Ephemeroptera, in particular the Baetidae, most numerous across sites.

 There were, nevertheless, differences in community structure between sites, which were related closely to stream physicochemistry. Ordination scores were strongly correlated with altitude, magnesium concentration and substratum composition. Classification was also linked to altitude and chemistry, differentiating high‐altitude sites with low silica concentrations from others. Sites from the Anapurna and Everest regions, with their contrasting chemistry, were also separated.

 Community structure was also related to land use: streams draining catchments dominated by terraced agriculture had different communities from those in scrub or forest. This result was confounded, however, by the strong relationship between land use, altitude and chemistry; sites in terracing were at lower altitude, had higher concentrations of silica and a higher proportion of fine sediments than those in the other land‐use types.

 Overall, our data indicate that natural features of the relief and geology in the Himalaya create strong gradients in their invertebrate faunas, but that activities of man may have an effect on stream structure and ecology through catchment management.
The effect of temperature on morphology, life history and growth rate of Filinia terminalis (Plate) and Filinia cf. pejleri Hutchinson in culture
Authors: SANOAMUANG LA‐ORSRI
Published: May 2006

Experiments on the influence of temperature (5–25°C) on morphology, life history and growth rate of Filinia terminalis and F. cf. pejleri were performed in replicated individual cultures with Oocystis sp. as food.

 Some morphological characteristics previously used for the identification of both species were found to be affected by temperature and also by life cycle stage. However, numbers of unci teeth were not affected.

 Body and setal lengths, life spans, all stages of development, and growth rates of both species decreased with increasing temperature.

 Offspring number per female of both rotifers was highest at 20°C. Maximum growth rate of F. terminalis was at 25°C, whereas that of F. cf. pejleri was at 20°C.
Impact of larval Dorosoma predation on Daphnia parvula dynamics
Authors: SHAHADY THOMAS D.
Published: May 2006

In reservoirs of the south‐eastern United States, Daphnia typically decline in abundance during the summer months. Current understanding suggests that adult shad (Dorosoma spp.), the dominant planktivore in these reservoirs, plays a limited role in Daphnia midsummer declines. The impact of shad larvae is beginning to be documented.

 To examine the impact of larval shad on Daphnia seasonal dynamics, larval dynamics were studied over two seasons and stomach contents were analysed during one season.

 Initial Daphnia panwla declines correlated with abundance of shad larvae. During the decline, shad stomach contents consisted of 97—100%D. parvula. After D. parvula declined, Bosmina and Diaphanosoma accounted for up to 97% of larval diets. When shad diets included other cladocerans, D. parvula abundance increased in the reservoir.

 When this predation pattern was incorporated into a predictive model, larval shad predation accounted for an initial, temporary decline in D. parvula abundance. However, when other crustaceans were incorporated into the shad diet, D. parvula populations increased.

 These results suggest that larval shad have a temporary, strong influence on the structure and abundance of D. parvula populations in south‐eastern reservoirs of the United States.
Predation on ciliates by freshwater calanoid copepods: rates of predation and relative vulnerabilities of prey
Authors: BURNS CAROLYN W. , GILBERT JOHN J.
Published: May 2006

The susceptibility of ciliates in a mesotrophic lake to predation by Epischura lacustris, Diaptomus minutus and D. pygmaeus was assessed during summer. Oligotrichs, particularly Strobilidium velox (c. 43 μm), were removed efficiently by adult copepods and contributed substantially to the diet of female D. minutus. The presence of approximately 1,6 adult Epischura 1‐−1, or sixteen adult female Diaptomus 1‐−1, could halt the growth of S. vechx populations in summer.

 Factors affecting the rate at which copepods prey on ciliates were examined in experiments with D. pygmaeus and cultured ciliates. Rate of predation on S. velox, the preferred species, became saturated at 5 S. velox ml−1 (45ngCml−1) and did not change with a 10‐fold increase in alternative algal food.

 Behavioural differences among ciliates, and the presence of other ciliates, contributed to differences in ciliate susceptibility to predation and suggest reasons why rates of removal of ciliates are not related to ciliate size.

 By feeding selectively, at high rates, calanoids may suppress populations of some ciliates and thereby influence microzooplankton community structure.
Seasonal variation in pH and alkalinity and recruitment of sunfish populations
Authors: JARRETT J.N. , CUTLER M.B. , EBERSOLE J.P. , HAGAR W.G.
Published: May 2006

In a study of five ponds sensitive to acid precipitation, we document seasonal acidification profiles and assess the impact of short‐term acid pulses on the reproductive success of resident sunfish (Lepomis spp.).

 Three years of water sampling at 2–3 week intervals showed substantial seasonal variation in pH and alkalinity consistent with a carbonate buffering system. Though all ponds shared a common seasonal pattern in pH, ponds with relatively low pH and alkalinity showed the greatest variation in these parameters. Spring minima may dispose some of the ponds towards episodes of extreme acidity during heavy spring rains.

 Otolith analysis of young‐of‐the‐year sunfish revealed recruitment failures for eggs laid early in spring in ponds with relatively low alkalinity and pH, and, in the most extreme case, missing day classes at subsequent irregular intervals even though average pH and alkalinity were well above those demonstrated to affect centrarchid fishes.

 Age‐class distributions of sunfishes revealed gaps in adult age distributions which could be traced through 3 years of the study, but there was no clear‐cut relationship between pond acidification and the age structure of adult fish.

 Seasonal profiles of acidity may enable researchers to predict the time during which a pond or lake may be highly sensitive to acid inputs. Comparative otolith analysis of young‐of‐the‐year fishes and short‐term continuous monitoring of water chemistry may provide an early warning of biological effects of acidification in sensitive bodies of water.
Trophic coupling within the microbial food web: a study with fine temporal resolution in a eutrophic freshwater ecosystem
Authors: BERNINGER ULRIKE‐G. , WICKHAM STEPHEN A. , FINLAY BLAND J.
Published: May 2006

The major components of the microbial food web (dissolved organic carbon, bacteria, protozoa, rotifers and algae) of Priest Pot, a small freshwater pond, were investigated over a period of 5 months. Water samples were collected from the epilimnion every 1–3 days.

 Time series analysis helped identify the trophic relationships within the planktonic community. There were strong predator—prey relationships between both ciliates and large rotifers and the total nanoplankton, between rotifers and small ciliates and between the total microzooplankton community and phytoplankton. Small rotifers and small ciliates probably share the same food resources. The major bacterivores in the system could not be identified with our methods. However, our previous results point to a dominating role of nanoplanktonic (2–20 μm) heterotrophic protists as the main grazers of bacteria.

 Rotifers are the major type of metazoan zooplankton in Priest Pot; crustacean zooplankton are absent from the community. Bacterial production probably reaches rotifers via a variety of pathways: there may be a three‐step link from bacteria to bacterivorous nanoplankton, to ciliates and then to rotifers. Furthermore, a strong correlation between the nanoplankton and rotifers suggests a direct link between these components, implying a much shorter pathway. Some of the rotifers in the pond can graze directly on bacteria, and many of the larger planktonic organisms (large ciliates and rotifers) are algivores. The latter two predator—prey relationships suggest an efficient transfer of bacterial and primary production to higher trophic levels.
The limnology of Lac ďIfni (High Atlas Mountains, Morocco), an unusually productive mountain lake
Authors: GEE JOHN H.R. , DUIGAN CATHERINE A.
Published: May 2006

Lac ďIfni (surface area 30 ha, zmax 60 m, altitude 2300 m) lies in a catchment comprised of Precambrian igneous rocks in the High Atlas Mountains of Morocco. Previously described as a typical ohgotrophic lake, it was also reported to have a warm layer at the base of the hypolimnion which was ascribed to phreatic water supply and drainage.

 Visits to the lake made in May/June and September 1990 showed strong thermal stratification but no hypolimnial warm layer. Drainage from the lake is subterranean, through a natural rubble dam, and the water level dropped by at least 7m through the summer. The flushing rate is about 0.6 year−1.

 The upper part of the metalimnion and the lower epilimnion were strongly supersaturated with oxygen in June, and there was a pH gradient from 7 to 10.5 between the hypolimnion and the epilimnion. These features were less marked in September when planktonic gross primary productivity was estimated to be about 145mgCm−2 h−1. In September the hypolimnion was 38% saturated with oxygen; the areal hypolimnetic oxygen deficit between June and September was 0.073mg O2 cm−2 day−1. Total dissolved phosphate concentrations were 7–14 μgl−1.

 The open water faunal assemblage consisted of Brachionus calyciflorus and Filinia lotigiseta (Rotifera), Cyclops abyssorum (Copepoda), and stunted Salmo trutta (Pisces). Trout diets were comprised principally of adult copepods and copepodites, which showed diurnal vertical migration, and of algal material apparently scraped from rock surfaces. The dry biomass density of Cyclops was at least 2gm−2 in June and at least 4.1 gm −2 in September.

 Tubifex tubifex (Oligochaeta) dominated the benthos below depths of 40m. Mean dry biomass density was 2.8gm−2, but ranged from 0.6–8.1 gm−2 between samples. About 50% of the lake bottom is below 40m depth.

 The persistent oxygen supersaruration of the euphoric zone, the field estimate of primary productivity, the hypolimnetic oxygen deficit, the biomass of zooplankton and the benthic biomass together indicate that Lac ďIfni is an unusually productive mountain lake. This high level of productivity may be sustained by nutrient addition through contamination by dust originating outside the catchment, aided by efficient nutrient recycling in the euphoric zone.
Response to Frutiger & Schib (1993) ‘Limitations of FST hemispheres in lotic benthos research’
Authors: STATZNER B.
Published: May 2006

This response to the paper of Frutiger & Schib (1993) focuses on substantial errors that are relevant to the interpretation of results and deficiencies in their study design. I include some reanalysis of the original data of Schib (1991), which formed the basis of Frutiger & Schib's paper.

 The paper of Frutiger & Schib (1993) is flawed because of their sampling strategy (sequence of measurements, depth stratification, and the long duration of the study in relation to temporal changes in the insect populations), the selection of study sites (one lake outlet, one river disturbed by bathers), the mixing of single‐species and multiple‐species units in the analysis, the pooling of data and its analysis, the omission of essential information given by Schib (1991), and the generation of doubtful arguments. Their approach and interpretation places FST hemispheres at an unreasonable disadvantage in a debate about the relative utility of hemispheres and propeller‐type current meters and consistently discriminates against the general role hydraulics play in the micro‐distribution of the eight insect taxa that were studied.

 Despite the deficiencies of their study, my reanalysis of the original data of Schib (1991) provides significant models of insect abundance in relation to hemisphere density for six of the eight insect taxa, with r2 values between 0.62 and 0.86 for five of them.
Influence of nymphal size, sex and morphotype on microdistribution of Deleatidium (Ephemeroptera: Leptophlebiidae) in a New Zealand river
Authors: COLLIER KEVIN
Published: May 2006

The interaction of water depth and velocity with size, sex and morphotype of nymphs belonging to the leptophlebiid mayfly genus Deleatidium was investigated in a New Zealand river.

 Velocity had a significant effect on distribution such that larger nymphs tended to be found more commonly in faster water. Depth also influenced size distribution, but in different ways at different sites.

 Water velocity or depth alone did not significantly influence the distribution of sexes (1.0 mm head width), but the combined effect of these two factors was significant. Final instar males appeared to be relatively more abundant in slower water than final instar females.

 Nymphs (1.0 mm head width) belonging to the informal lillii group (apically pointed gills) were present over a wide range of depth and velocity conditions, but those belonging to the myzobranchia group (round‐tipped gills) were largely restricted to fast water (>0.9ms−1).

 Several mechanisms thought to cause variations in microdistribution are discussed. These include differential effects of oxygen availability, food requirements and drag forces, nymphal behaviour, and selection of oviposition sites by adults.
Allozyme variation among natural populations of Holopedium gibberum (Crustacea; Cladocera)
Authors: THIER EDWARD
Published: May 2006

Holopedium gibberum, from twenty lakes in Rhode Island and Maine, were examined for allozyme variation at five loci to determine the pattern and degree of generic variation among sites and the genetic structure within individual lakes.

 There were significant differences in allele frequencies among sites. Most populations were fixed for a particular allele at each locus. Only five lakes had polymorphic populations.

 Polymorphic populations showed significant deviation from expected Hardy‐Weinberg genotype frequencies. In each case, there was an excess of homozygotes.

 Two lakes were examined for intra‐lake allele frequency differences. In one lake there were no differences. The other lake exhibited significant allele frequency differences between stations at the north and south ends of the lake.

 Populations were examined for the frequency distribution of composite genotypes over three loci. Most populations were dominated by one or two genotypes.

 The results suggest sporadic sexual recruitment and a high degree of genetic isolation among these populations of H. gibberum. In these respects they resemble the permanent pond populations of Daphnia magna examined by Hebert (1974a).
Nutritional suitability of some uni‐algal diets for freshwater calanoids: unexpected inadequacies of commonly used edible greens and others
Authors: HART ROB C. , SANTER BARBARA
Published: May 2006

Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Tropodiaptomus spectabilis) were measured on mono‐specific diets of comparably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas sp., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capricornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17°C) and food supply level (1 mgCl−1).

 All diets other than Scenedesmus and Selenastrum supported complete naupliar development at broadly comparable times within and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between diet types, and both Chlamydomonas and Cyclotella were inferior or inadequate for copepodid development.

 Both naupliar and copepodid stages ingested radiolabelled Scenedesmus and Selenastrum readily. Comparative incorporation rate measures of Selenastrum and Cryptomonas respectively exceeded estimated metabolic maintenance needs of stage 3/4 nauplii of T. spectabilis by some 56% and 790%. Scope for growth (‘surplus’ energy) was accordingly fourteen‐fold greater on Cryptomonas than on Selenastrum /Scenedesmus. The dietary inadequacy of these two green algae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.
Interactions between a stream caddisfly and the algae on its case: factors affecting algal quantity
Authors: BERGEY ELIZABETH A. , RESH VINCENT H.
Published: May 2006

1. Field experiments were conducted to examine interactions between larvae of the caddisfly Gumaga nigricula and the algae (primarily diatoms) located on their sand grain cases. Floating experimental enclosures were placed in sunlit pools of a California stream. Treatments applied to occupied cases, or to those from which caddisflies had been removed, included variations in grazer density, addition of nutrients, and modification of illumination using shade cloth.

2. Neither faecal‐enriched agar in empty cases nor injections of faecal material into plugged cases affected case chlorophyll a concentration; injected nutrients (N and P), however, did increase chlorophyll a concentration. Faecal material may be nutrient poor, or nutrients may not be readily released. In addition, the relatively impermeable case wall may reduce the likelihood that nutrients from caddisflies reach the algae on the outer case surface.

3. Although a Gumaga larva may graze algae from its own case, grazing by conspecifics and the caddisfly Helicopsyche borealis causes a greater reduction in the chlorophyll a content of cases.

4. Chlorophyll a content of empty cases was decreased by experimental reduction of light. Because of shading associated with burrowing, chlorophyll a content of cases occupied by Gumaga was low and was unaffected by experimental light reduction.

5. Removal of Gumaga from its case results in rapid accrual of algae. Thus, the net effect of larval presence is to diminish the algal content of its case.
The effect of sample duration on the quantification of stream drift
Authors: CULP JOSEPH M. , SCRIMGEOUR GARRY J. , BEERS CHRIS E.
Published: May 2006

1. We performed computer simulations and a field experiment to determine the effect that sample duration and, thus, sample volume had on estimates of drift density and sample variance.

2. In computer simulations, when the spatial arrangement of individuals in the water column approximated a random and a contagious‐random distribution, estimated mean drift density was not significantly affected by sample duration, but sample variance decreased curvilinearly as sample duration increased.

3. Similar results were obtained in field experiments in habitats of high and low water velocity.

4. Our findings from an Albertan stream indicate that the relationship between sample variance (i.e. coefficient of variation) and duration of drift samples is curvilinear. This relationship affected the number of samples required to achieve a specific level of precision (i.e. a standard error within 10% of the mean). For estimates in low and high current velocities, sample variation was halved by increasing the duration of sample collections from 10 to 20 min. The increased precision obtained with samples of 20 min duration reduced the amount of drift material that needed to be processed by approximately 50% compared with an equivalent 10% level of precision for samples of 10 min duration. This reduction in the number of samples required to obtain a given level of precision has important consequences to the cost of processing drift samples.

5. Thus to optimize studies of stream invertebrate drift, both in terms of sample precision and processing effort, researchers must consider the effect that sample volume has on the variance of drift density estimates. Because researchers generally use drift nets with similar‐sized apertures (>300cm2), the problem for specific field applications becomes one of optimizing sample duration relative to variance estimates for drift density.
Influence of phytoplankton on the response of bacterioplankton growth to nutrient enrichment
Authors: WANG LIZHU , PRISCU JOHN C.
Published: May 2006

1. Laboratory experiments were conducted to test the effect of nutrient enrichment on bacterioplankton growth in the presence and absence of phytoplankton.

2. In one series of experiments, bacterioplankton growth in terms of specific activity [3H‐thymidine incorporation (cell number)−1] was greater in whole lake water samples than in samples from which phytoplankton had been removed by filtration (1.0 μm), regardless of the nutrient enrichments (control, NH+4 plus PO3‐4 and mannitol). Organic C enhanced bacterioplankton growth in both whole and filtered lake water.

3. In another series of experiments (with the same nutrient enrichments as in the first experiment except that glucose replaced mannitol), bacterioplankton growth in whole lake water enriched with PO3‐4 plus NH+4 and incubated in the light was greater than in two treatments designed to inhibit photosynthetic activity (+DCMU and dark). Bacterioplankton response to nutrient addition was greatest in the PO3‐4 plus NH+4 enrichment under all three conditions (light +DCMU, and dark).

4. These results indicate that bacterioplankton growth could be directly limited by inorganic P and N when these elements are in short supply. Enhancement of bacterioplankton growth by phytoplankton occurs only under PO3‐4 and NH+4 replete environments.
Origins, structure, and trophic significance of amorphous seston in a blackwater river
Authors: CARLOUGH LESLIE A.
Published: May 2006

1. The role of suspended organic aggregates in aquatic systems has received much attention, but their origin and function vary between environments and conditions.

2. In the Ogeechee River (Georgia, U.S.A.) particles are constructed of clay, organic debris, and microorganisms in a matrix of mucopolysaccharide fibrils. Although these fibrils are probably of bacterial origin, microcosm studies suggest that synthesis of particles from dissolved substances can occur in the absence of microbial processing.

3. Processing of organic material and production of amorphous aggregates occurs through a series of microbial events and follows a well‐defined successional cycle that results in a high concentration of protists in sestonic particles.

4. Chemical analyses show that the relatively high protein and fat content of this amorphous material is a valuable food resource for filter‐feeding macroinvertebrates that are dense in this system.
Toxicity to Daphnia of a compound extracted from laboratory and natural Microcystis spp., and the role of microcystins
Authors: JUNGMANN DIRK , BENNDORF JÜRGEN
Published: May 2006

1. The microcystin content of a variety of Microcystis spp., from both laboratory strains and natural blooms, was analysed by HPLC. The microcystin content of laboratory strains ranged from 1.6 to 4.3μgmg−1 dry weight. Yearly and seasonal variation was detected in an analysis of bloom material collected from Bautzen Reservoir over a 3‐year period. The microcystin concentration in bloom material ranged from undetectable to 1.16 μg ml−1 dry weight.

2. Toxicity of laboratory and natural Microcystis to Daphnia pulicaria was determined using an established LC50 technique. Partially purified water extracts from different Microcystis samples exhibited a wide range of toxicity. The highest activity was found in natural Microcystis samples, with an LC50 of 36 μgm−1 dry weight of Microcystis, whereas one strain did not appear toxic at 1600 μg ml−1.

3. No correlation was found between the concentrations of microcystins of different laboratory and natural Microcystis strains and the toxicity of extracts to Daphnia pulicaria from the same strains. Therefore, we discriminated between hepatotoxic microcystins and the compound(s) that is toxic to Daphnia, here termed DTC (Daphnia‐toxic compound), which is independent of microcystins.
Body size and abundance of benthic animals in Mirror Lake, New Hampshire
Authors: STRAYER DAVID L.
Published: May 2006

1. There is a strong negative correlation between body mass and population density for 192 species from the zoobenthos of Mirror Lake, a small, oligotrophic lake. This correlation spans seven—nine orders of magnitude in body mass.

2. The slopes of both the regression and the upper bound on the distribution of data points are significantly shallower than ‐0.75, the slope that has been suggested to imply that metabolic constraints limit animal abundance.

3. The regressions for individual taxonomic groups (i.e. classes, phyla) do not conform closely to the overall regression line.

4. It is suggested that metabolic constraints on community structure need not be expressed by a slope of ‐0.75 for regressions (or upper bounds) on body mass—abundance functions.
Relationships between macroinvertebrate communities and environmental variables in metal‐contaminated streams in south‐west England
Authors: GOWER A.M. , MYERS G. , KENT M. , FOULKES M.E.
Published: May 2006

1. Macroinvertebrate species and information on thirty‐nine variables were recorded at forty‐six sites on twelve Cornish streams affected to varying extents by past metalliferous mining.

2. Relationships between macroinvertebrate communities and environmental variables were examined using canonical correspondence analysis (CCA). Copper was the strongest correlate with Axis 1 of the analysis, suggesting that it may have a major role in determining community structure. There were also strong correlations between Axis 1 and aluminium, alkalinity, pH, dissolved organic matter and algal cover, and between Axis 2 and discharge.

3. CCA distinguished four site groupings. In spite of seasonal changes in position on the ordination, as revealed through CCA and detrended correspondence analysis (DCA), sites retained their group membership. There were differences in the proportions of the major taxa within the four CCA‐derived groups. In the group with the highest copper concentration, Ephemeroptera were absent, but triclads and chironomids were abundant, with Orthocladiinae the dominant group.

4. Changes in the occurrence of species along the metal gradient reflected changes in sensitivity. Tolerance' plots of selected species based on the CCA site ordination diagram were used to identify environmental thresholds.

5. As well as direct toxic effects of copper and aluminium on invertebrate communities, co‐precipitation of these two metals could be an important physical factor. Further modifying influences resulting from interactions between toxic metals and pH, alkalinity, hardness and dissolved organic matter contributed to the complexity of conditions affecting the faunal community in metal‐contaminated streams.

6. The most severely contaminated sites, with mean copper concentration exceeding 500 μgl−1, were all characterized by a reduced community dominated by the flatworm Phagocata vitta, the chironomids Chaetodadius melaleucus and Eukiefferiella claripennis and the net‐spinning caddis Plectrocnemia conspersa. The necessity for species identification is demonstrated in relation to variation in metal tolerance.
Long‐term effects of PO4 fertilization on the distribution of bryophytes in an arctic river
Authors: BOWDEN WILLIAM B. , FINLAY JACQUES C. , MALONEY PATRICIA E.
Published: May 2006

1. Each year since 1983, H3PO4 has been added continuously during the ice‐free season to a P‐limited tundra river (Kuparuk River, North Slope, Alaska). Effects on epilithic metabolism, invertebrate community structure and fish production developed quickly.

2. In 1990, 7 years after fertilization began, we noted extensive coverage by bryophytes within the fertilized reach of the river, where very little had been noted before. Bryophyte biomass from a limited set of quadrats taken in 1990 and 1991 yielded 17 ± 9 (SE) g dry mass m−2 in control reaches and 322 ± 96 g dry mass m−2 in fertilized reaches.

3. An initial survey of macroalgal and bryophyte cover in 1991 suggested that the moss Schistidium (Grimmia) agassizii was distributed in both control and fertilized reaches of the river. No clear difference in coverage by this species was found in either reach.

4. In contrast, two species of Hygrohypnum (H. alpestre and H. ochraceum) were found almost exclusively in the fertilized reach. An extensive point transect survey done in 1992, above, within and below the fertilized reach, indicated that increased cover and biomass of Hygrohypnum spp. were confined to the fertilized reach of the river. Detrended correspondence analysis clearly separated the macrophyte and macroalgal communities in the fertilized reach from those in the control and downstream reaches.

5. A fourth bryophyte species (Fontinalis neomexicana) also occurred almost exclusively in the fertilized reach, but was much less abundant than the Hygrohypnum species.

6. Analysis of total N and P in the tissues of the Hygrohypnum spp., and estimates of average coverage (∼15%) and biomass (∼150g dry weight m−2) over an 8km fertilized reach, suggest that these species alone may have removed two‐thirds of the P added in the fertilizer experiment. The bryophyte community in this river is likely to be the dominant sink for P in the fertilized reach.
Feeding ecology of the diving ducks pochard (Aythya ferina), tufted duck (A. fuligula), scaup (A. mania) and goldeneye (Bucephala clangula) overwintering on Lough Neagh, Northern Ireland
Authors: WINFIELD IAN J. , WINFIELD DEMISE K.
Published: May 2006

1. The diets of pochard (Aythya ferina), scaup (A. marila) and goldeneye (Bucephala clangula) overwintering on Lough Neagh are dominated by chironomid larvae, while molluscs are more important in that of tufted duck (A. fuligula).

2. Inshore areas of Lough Neagh offer poor feeding conditions for these diving ducks because chironomid larvae and molluscs are of small individual body size or low abundance. These factors lead to all four ducks foraging at least in part at depths greater than those usually exploited.

3. Due to their common consumption of molluscs, the diet of tufted duck shows a higher overlap with that of an introduced roach (Rutilus rutilus) population than with any other duck or fish species.

4. The feeding ecology of tufted duck and roach in Lough Neagh may form an example of distant competition and be at least partly responsible for recent fluctuations in the numbers of tufted duck.