bluuebunny/crossref_metadata_2025 huggingface dataset:
Resting eggs of lake‐ Daphnia I. Distribution, abundance and hatching of eggs collected from various depths in lake sediments
Authors: CARVALHO GARY R. , WOLF HANS GEORG
Published: May 2006

SUMMARY. 1. Resting eggs (ephippia) of Daphnia galeata, D. hyalina, D. cucullata and D. galeata X D. hyalina hybrids were collected from the upper 8 cm of sediments at various water depths from two glacial lakes in the Northern Federal Republic of Germany.

2. The horizontal distribution of ‘intact’ ephippia (i.e. those containing two apparently healthy eggs) was extremely patchy, with mean densities in the upper 8 cm ranging from 1325 to 113,907 m−2 (coefficient of variation, C=65.5%; Schöhsee, Holstein) and 25,343–159,143 m−2 (C=58.5%; Kel‐lersee. Holstein). Ephippial densities were greatest in sediments from deep waters. The highest densities of intact ephippia were in the upper 4 cm of sediment, with progressively fewer with increasing depth.

3. A proportion of eggs obtained from sediments during autumn (September‐November 1985) and spring (March‐May 1986) were exposed to continuous light (approximately 18 W m−2) at three temperatures (6, 12, 20°C), and the incidence of hatches recorded.

4. Hatching success was consistently low (maximum 14.4%), with most hatching occurring at 12°C. There was no significant difference between the hatching success of ephippia collected during autumn and spring. Decapsulation of ephippial eggs inhibited hatching. Hatching was highly synchronous within each treatment, and the pattern did not differ significantly with sediment depth, though hatching success was lower in deep sediments. A huge reservoir of ephippia is present in lake sediments, of which a proportion may remain viable for many years. Periodic recruitment of hatchlings to the pelagic population may provide an important mechanism for the maintenance of genetic diversity in Daphnia populations, as well as affecting rates of evolutionary change.
Resting eggs of lake‐Daphania II. In situ observations on the hatching of eggs and their contribution to population and community structure
Authors: WOLF HANS GEORG , CARVALHO GARY R.
Published: May 2006

SUMMARY. 1. To investigate the contribution of hatchlings from lake‐Daphnia resting eggs (ephippia) to population and community structure, hatching was monitored in situ from April to November 1986 in two north German lakes. Hatching traps were placed on the sediments and the incidence, genetic and species composition of ephippial hatchlings determined twice‐weekly.

2. Hatching began in April after the thawing of ice. and continued for 3–4 weeks until the lakes stratified. There was no obvious relationship between the onset and duration of hatching and the environmental variables recorded, namely Secchi depth, surface temperature, temperature and oxygen concentration at the sediment‐water interface.

3. Among the hatchlings were D. galeata, D. hyalina and their interspecific hybrid.

4. In the lake which contained overwintering animals the number of ephippial hatchlings was approximately one third of the total number of juveniles present in the lake.

5. In the second lake, no adults were recorded during winter and the population was probably founded by ephippial hatchlings alone. There was good agreement, in the short term, between the proportion of each species represented among hatchlings and the subsequent species composition in the lake.

6. The hatchlings were genetically diverse, and alleles were representative of those alleles present in contemporary populations.
Wild brown trout Salmo trutta: an important national and international resource
Authors: ELLIOTT J. M.
Published: May 2006

SUMMARY. 1. Brown trout were once given a variety of latin and common names, but are now regarded as belonging to only one polymorphic species, Salmo trutta L. A review of their geographical distribution shows that this species was originally native to Europe but has been successfully introduced in at least twenty‐four countries outside Europe.

2. Brown trout provide valuable commercial and sports fisheries, e.g. commercial and rod catches of sea‐trout in England and Wales averaged 110,547 fish per year from 1983 to 1986 and the minimum value of these fisheries is estimated to be £55M.

3. It is concluded from this brief review that the major objectives of scientific research on wild brown trout should be: (a) an assessment of the current status of stocks; (b) the maintenance of existing populations; (c) the development and improvement of mathematical models that can be used as tools for the conservation and management of this important national and international resource.
Conservation and management of brown trout, Salmo trutta, in Scotland: an historical review and the future
Authors: MILLS DEREK
Published: May 2006

SUMMARY. 1. Intensive research into the life history of brown trout started In 1948 when the Brown Trout Laboratory was opened in Pitlochry. Over the next 15 years significant contributions were made to the brown trout literature upon which the Laboratory based advice to landowners and anglers wanting to develop their fisheries.

2. Increasing pressure from the government for more work on Atlantic salmon tended to divert research funds and time away from brown trout investigations. The International Biological Programme's major study at Loch Leven from 1966 to 1972 ensured a continuing interest in trout in standing waters. Over this period little attention had been paid to trout in rivers. This changed when a number of investigations were started on the River Tweed by Edinburgh University.

3. A major constraint to brown trout conservation and management has been illegal fishing and lack of records on stocking activities and catches. The granting of Protection Orders under the Freshwater and Salmon Fisheries (Scotland) Act, 1976, has been a major incentive to increased interest in the improvement of trout fisheries.

4. Brown trout stocks have been reduced in certain areas due to the effects of afforestation, acidification, land drainage and farm wastes. Various remedial measures have been proposed and implemented.

5. To meet the increasing demands for trout fishing, many loch and reservoir fisheries are now stocked with rainbow trout in preference to brown trout. Attention should be paid to the interaction of these two species in both standing and in running waters., where fish farm escapees and inadvisable releases go unrecorded.

7. Research into the genetic effects on wild stocks from the liberation of large numbers of hatchery‐reared brown trout has been lacking and probably many ‘pure’ indigenous stocks have been lost. More work in this field is essential.

8. Proposals are outlined for future brown trout research and recommendations are made for better management. Suggestions are also put forward for changes in the legislation to further protect Scottish brown trout stocks.
Changes in Na, K, Ca, Mg and Al content of submersed leaf litter, related to ingestion by the amphipod Gammarus pulex (L.)
Authors: CHAMIER ANNE‐CAROLE , SUTCLIFFE DAVID W. , LISHMAN JEAN P.
Published: May 2006

SUMMARY. 1. Changes in the amounts of Na, K, Ca, Mg and Al in fallen leaves of oak, alder and mat grass were measured during 13 weeks of submersion in seven streams differing in pH and ionic content.

2. In the first 2 weeks, Na, K and Mg leached from the leaves, but in the following weeks there was a net increase of Al, K and Mg and, in some instances, Na and Ca. Increases of K and Mg were relatively larger in circumneutral streams whereas the greatest increases of Al occurred in acid streams. Net gains are attributed to absorption of cations from water by saprophytic micro‐organisms degrading the leaves, direct adsorption of Al on to leaf tissues ‐ especially in acid streams ‐ and capture of small particles of magnesium and aluminium silicates (clays).

3. Daily ingestion of elements was calculated as a percentage of whole body contents in Gammarus pulex (L.) and compared with daily loss rates. Leaf litter may be an important source of some major elements for ionic balance in juvenile G. pulex and a major source for uptake of potentially toxic aluminium in acidic, soft waters.
Patterns of benthic invertebrate assemblages in rivers of northwestern North America
Authors: CORKUM LYNDA D.
Published: May 2006

SUMMARY. 1. Biogeographical and on‐site. hydrological variables were evaluated to determine spatial distribution of benthic invertebrate assemblages at 100 river sites in northwestern North America.

2. Results of cluster analysis suggested that the river sites comprised sixgroups (A‐F), each supporting a characteristic invertebrate assemblage.Distinct groups were best represented by abundant Tricorythidae (C), Amphipoda (F), Rhyacophilidae and Systellognatha (E), and Elmidae and Hydroptilidae (A). Brachycentridae (B) and Oligochaeta (D) were widespread throughout the study area.

2. Both biogeographical and hydrological features contributed to the correct classification of site groupings characterized by distinctive fauna. However, biogeographical features were more useful than variables measured at the river site in discriminating among the site groupings.Groups C and F were most prevalent within the Hudson Bay drainage.Groups A, C and F were typically located within plains; group E sites were in mountainous regions.

4. The hydrological variables most useful in delineating site groupings were mean current velocity and mean depth. Slow, deep waters characterized amphipod sites; shallow, fast flowing waters occurred at Rhyacophilidae Sysellognatha sites.

5. Results substantiate previous views of a strong association between benthic invertebrates in small rivers and the terrestrial biome through which the river flows.
The causes of change in the diversity and stability of phytoplankton communities in small lakes
Authors: ELBER FREDY , SCHANZ FERDINAND
Published: May 2006

SUMMARY. 1. A study of the diversity and stability of phytoplankton communities during one vegetation period (February‐October 1984) was carried out in four small lakes in the Pfynwald region of Canton Valais, Switzerland: Kaminsee I, Kaminsee II, Grossee and Rosensee. The diversity was calculated according to Shannon & Weaver (1949). The change in diversity ΔH; and SIMI (similarity index according to Stander. 1970) were used as measures of stability.

2. On average, the diversity was highest in the oligotrophic Rosensee (annual mean 3.19) and least in the hypereutrophic Kaminsee I (annual mean 1.34). In Kaminsee I and Grossee, the diversity corresponded in the main to the relative frequency of Cryptomonas erosa Ehrenberg: i.e. the diversity was low when the relative frequency of C. erosa was high and vice versa (Kaminsee I: max. diversity 2.74; min. 0.13. Grossee: max. 3.62; min. 0.28; annual mean 2.21). Kaminsee II and Rosensee exhibited only slight variations in their phytoplankton community structure (Kaminsee II: max. diversity 2.83; min. 1.26; annual mean 2.10. Rosensee: max. 3.79; min. 2.81). High values of diversity, or increases in diversity, were a result of low nutrient availability and grazing pressure. Lower diversity values. or decreases in diversity, were a result of a plentiful nutrient supply, low grazing pressure and grazer selectivity with respect to food organisms.

3. Because values of the diversity index vary by different amounts during the course of a year depending on the water body, the characterization of a phytoplankton community on the basis of one value alone is unsatisfactory. It is suggested that the mean and either standard deviation or range of the diversity be cited in order to overcome this drawback at least partially.

4. No generally accepted measure exists for the calculation of stability. According to the measure of stability employed, a community may appear to be more or less stable. A statement concerning the stability of a community without mentioning the measure employed is therefore worthless. The factors determining the stability of a phytoplankton community do not have the same effect on all measures of stability.

5. The change in diversity ΔH’was influenced in the main by alterations
An ecologically useful classification of mean and near‐bed flows in streams and rivers
Authors: DAVIS J. A. , BARMUTA L. A.
Published: May 2006

SUMMARY. 1. Mean motion and near‐bed flows in streams and rivers can be described using a classification derived from fairly simple field measurements. Our proposed classification is ecologically useful because it incorporates the combined effects of velocity, depth and substrate roughness to provide a means of quantifying the flow regimes occurring within the microhabitats of stream benthos.

2. Mean motion is characterized by the Reynolds number and the Froude number. Both are easily calculated, and because they are dimensionless they provide a means of comparing flows at different sites.

3. Five categories of near‐bed flows (i.e. the flow microenvironments of stream benthos) are recognized. Flow may be hydraulically smooth or hydraulically rough and the latter category is subdivided further into: chaotic flow, wake interference flow, isolated roughness flow and skimming flow. Hydraulically smooth flows occur in sections of a river bed with fine sediments (e.g. sands, muds and clays). over flat sheets of bedrock, or in association with the flat blades of submerged macrophytes. Hydraulically rough flows occur where the substrate elements are larger (e. g. pebbles, cobbles and boulders) and are a function of substrate roughness and the depth of flow relative to the height of the roughness elements. Chaotic flows and wake interference flows predominate in riffles whilst isolated roughness flows and skimming flows are more likely to be a feature of runs.

4. Conventional stream sampling methods (e.g. the Surber and box or cylinder samplers) may collect across several different flow microhabitats. Our classification should enable different flow microenvironments to be recognized and so sampled more appropriately which, in turn, may reduce apparent clumping and the wide confidence intervals of benthic population estimates. Because our classification identifies ‘patches’ within the flow regime associated with the stream bed it enables stream ecologists to generate testable hypotheses regarding the distribution and abundance of benthic species in response to flow.

5. Our classification identifies spatial patterns in the flow regimes associated with the stream bed. Temporal patterns have not been identified: however, predictable changes in spatial patterns will resuh from temporal changes in stream discharge.
Resistance of a cased caddis larva to accidental entry into the drift: the contribution of active and passive elements
Authors: WAR1NGER J. A.
Published: May 2006

SUMMARY. . 1. The resistance to passive entry into the drift of first to fifth instar larvae of Allogamus auricollis (Pictet, 1834), a case‐bearing caddis‐fly, was investigated in the laboratory using an artifical stream channel.

2. Dead larvae in their cases were exposed to different current speeds. When the heads of the larvae were directed towards the water flow (frontal position), the current necessary to wash larvae away ranged from 3 cm s‐l (first instars) to 21 cm s‐1 for fifth instars. When the larvae were at right angles to the current (lateral position), these speeds were 2 and 9cm s‐1, respectively. In terms of force (Newtons), this passive resistance to drift ranged from 0.3x10‐6 N (first instar, frontal position) to 307.0x10‐6 N (fifth instar, frontal position). The data obtained in the experiments were in good agreement with values calculated from hydrodynamic equations, using biometric parameters of the larvae.

3. Total resistance to drift was studied by exposing living larvae to different current speeds. The speed just sufficient to wash larvae away ranged from 13 cm s‐1 in the first instar to 27.9 cm s‐1 in the fifth instar (frontal position). In terms of force, the total resistance to drift varied between 5.3x10‐6 N (first instar) and 547.5x10‐6 N (last instar).

4. The difference between total and passive resistance to drift was defined as‘active resistance to drift', and is due to the effectiveness of a larva's attachment to the substrate. It ranged from 3.5x10‐6 N (first instar) to 222.8X 10‐6 N (last instar).
Parasitic regulation in a population of Boeckella hamata Brehm (Copepoda: Calanoida)
Authors: BURNS* CAROLYN W.
Published: May 2006

SUMMARY. 1. The impact of parasitism by a fungus Aphanomyces sp. (Phycomycetes: Saprotegniaceae) on a population of Boeckella hamata in Lake Mahinerangi in New Zealand was studied over 20 months. The incidence of infection among adult female copepods exceeded 12% throughout winter (May‐October) and was highest in autumn (46%) when population birth rates were depressed by 48.8%. During most of the study, parasitism lowered the rates of population recruitment and growth by more than 10%. These effects on the B. hamata population exceeded those of Aphanomyces on Boeckella dilatata Sars in another study.

2. It is hypothesized that the high incidence of parasitism by Aphanomyces and its importance at times in regulating populations of Boeckella in New Zealand lakes may be an ecological consequence of life in predator‐poor ecosystems.
Effects of small‐scale sedimentary patchiness on the distribution of tubificid and lumbriculid worms in Lake Geneva
Authors: LANG CLAUDE
Published: May 2006

SUMMARY. 1. The sediment consists of pillow‐like formations (0.7 m wide) separated by trenches, 0.2 m wide and 0.1 m deep, over large areas of Lake Geneva (Switzerland).

2. Biomass and total abundance of tubificid and lumbriculid worms were higher on the pillows than in the trenches. Potamothrix vejdovskyi, P. hammoniensis, P. heuscheri and Tubifex tubifex were more abundant on pillows whereas Peloscolex velutinus and Stylodrilus heringianus were relatively more abundant in the trenches.

3. These differences between worm communities suggested that organic sedimentation was higher on the pillows. Sedimentological analyses confirmed this interpretation.

4. Results of large‐scale surveys can be biased if sampling design is not adapted to such small‐scale patchiness.
Recent studies on long‐term changes in the sea
Authors: CUSHING D. H.
Published: May 2006

SUMMARY. 1. Long‐term changes in the sea have been described in fish stock records, the Californian Cooperative Fisheries program (Calcofi) and in the Continuous Plankton Recorder Program (CPR). Links between the recruitments to fish stocks have been established with temperature and they are coherent across broad areas and in time.

2. In the western North Sea between the fifties and seventies, phytoplankton and zooplankton declined by a factor of 5, to recover in the eighties. This event was linked to strong northerly winds and gales by which the time of onset of production in spring was delayed. Effects on fishes were shown in the oceanic tuna stocks, North Atlantic demersal stocks, Tasmanian lobsters and on the North Sea herring, all consequent on climatic changes.
Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams
Authors: COLLIER K. J. , WINTERBOURN M. J.
Published: May 2006

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies (Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.

2. Mean densities of larvae (range 234–2318 m−2) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m−2) was always highest at the stable, spring‐fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.

3. Annual production was high at the more stable, alkaline site (10.35 gLDW m−2) but much lower at the other sites (2.49–3.77 g m−2).

4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).

5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).

6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.
Interspecific differences in movement and hunting success in damselfly larvae (Zygoptera: Insecta): responses to prey availability and predation threat
Authors: JEFFRIES MICHAEL
Published: May 2006

SUMMARY. 1. Freshwater invertebrate predators can alter their hunting behaviour in response to prey availability and threat from their own enemies. Movement patterns and hunting success of the larvae of two species of damselfly (Zygoptera: Insecta), Enallagma cyathigerum (L.) and L. sponsa (Hansemann), were monitored in four combinations of prey availability and enemy threat. Aeshna juncea (L.) (Anisoptera: Insecta) larvae acted as predator and Daphnia magna Straus (Cladocera: Crustacea) as prey in the combinations: no predator/no prey; one Aeshna present/no prey; no predator/thirty Daphnia present; one Aeshna present/ thirty Daphnia present.

2. E. cyathigerum showed significantly reduced movement in the +Aeshna/no prey treatment but hunting success was not significantly affected. No other treatment effects were noted. L. sponsa movement patterns differed significantly across all four treatments and hunting success was significantly reduced in the presence of Aeshna.

Interspecifically, movement patterns of the two species differed markedly in all four treatments. L. sponsa larvae were much more active, and caught many more prey. Despite their activity L. sponsa larvae did not appear markedly more vulnerable than the immobile E. cyathigerum.

3. The interspecific differences between the two damselflies reflect predictions based on larval life‐history. Activity patterns and ability to capture adequate prey under varying levels of predation may be important in the ecology of damselfly species.
Short‐term productivity responses of algae and bacteria to zooplankton grazing in two freshwater lakes
Authors: SCHOENBERG STEVEN A.
Published: May 2006

SUMMARY. 1. The specific productivities of algae and bacteria were measured in short‐term (4 day) experiments consisting of enclosures with natural or reduced zooplankton biomass. Experiments were repeated five times over a season in each of two lakes that differed in the background concentration of dissolved organic carbon (DOC).

2. Algal biomass as estimated by chlorophyll a was suppressed in enclosures with ambient grazer levels in six of ten experiments and enhanced in one experiment. Distribution of chlorophyll among net and nanoplankton was not significantly affected by grazing.

3. Relative to enclosures with reduced zooplankton, normal grazer biomass (97–466μg 1−1 dry weight) enhanced specific algal productivity in only one of five experiments in the low DOC take and had no effect in all five experiments in the high DOC lake. The main effects of grazers on algae was through removal of biomass rather than through indirect changes in turnover rate.

4. Between experiments, bacterial density was either unaffected, or mildly enhanced (4–87%) in enclosures with ambient macrozooplankton compared to those with reduced levels. Bacterial productivity and turnover estimated by incorporation of [3H]thymidine into DNA showed different responses across experiments; increasing, declining or remaining the same with grazer minipulation. This variability was not related to differences in dissolved primary production or to background DOC between lakes or experiments. Comparison of bacterial productivities based on thymidine incorporation rates with changes in cell densities indicated that control of bacterial loss processes by macrozooplankton is more important than control of growth rates.
Simplified methods of estimating daily mean stream water temperature
Authors: CRISP D. T.
Published: May 2006

SUMMARY. 1. It was assumed that the average of twenty‐four hourly temperature readings is the‘true’daily mean. For a small stream in upper Tees‐dale, northern England, estimates of the daily mean were obtained from: (a) The mean of temperature readings taken at regular but less frequent intervals than hourly (twelve, six and three times per day), (b) The daily mid‐point (=1/2(maximum + minimum)). (c)Spot temperatures at the two times in the day when the daily temperature trace usually crosses the daily mean value. These estimates were then compared with the‘true’mean.

2. The accuracy of the estimate of daily mean decreased with reduced frequency of reading but, even at only three readings per day, was always within ±0.5°C of the true value. Consolidation of the daily estimates gave estimates of monthly and annual means within ±0.1°C of the true values.

3. Nearly 96% of estimates of the daily mean based on the daily midpoint were within ±0.5°C of the true value. The estimates showed a small but statistically significant positive bias.

4. Over 80% of estimates of the daily mean based on the‘first mean crossing’were within ±0.5°C of the true value and no bias could be shown.

5. Estimation of daily means from temperature at the time of the 'second mean crossing’was relatively complicated and gave less satisfactory results than did the first mean crossing.

6. The daily mid‐point and the temperature at the time of the first mean crossing both gave a good general indication of daily mean temperatures. When consolidated to monthly or annual means the estimates were within ±0.25°C and ±0.10°C, respectively, of the true values.
Population growth rates of two closely related rotifer species: effects of food quantity, particle size, and nutritional quality
Authors: ROTHHAUPT KARL O.
Published: May 2006

SUMMARY. 1. The relationship between population growth rates and the concentrations of several algal species was determined in laboratory experiments with the rotifers Brachionus rubens and B. calyciflorus.

2. The effects of food quantity were well described by a modified Monod model with a threshold for zero population growth. The model parameters depended on particle size and nutritional quality of the food algae. Differences between the rotifer species were significant and reflected their varying food‐size preferences.

3. For each rotifer species, thresholds were lowest for algae in the most readily ingested size range. The lowest thresholds were 0.07–0.09 mgC 1−1 with algae of about 5 μm equivalent spherical diameter (ESD) for B. rubens, and 0.19 mgC 1−1 with algae of about 10 μm ESD for B. calyciflorus.

4. Maximal growth rates (rmax) were slightly below 0.8 day−1 for both rotifers with most algal species. The highest rmax values for both rotifers were observed when Cyclotella meneghiniana was provided as food. With this alga, B. calyciflorus had a significantly higher rmax (1.02 day−1) than B. rubens (0.838 day−1).

5. From a comparison of the relationship between growth rates and ingestion rates, Chlamydomonas reinhardii appeared to be of low nutritional quality for B. rubens.

6. Egg ratios were related to growth rate and were not influenced by the algal food used. Egg development times and average mortality rates were estimated from the relationship between egg ratio and growth rate. B. calyciflorus appeared to have a high average mortality rate (0.383 day−1) compared to B. rubens (0.083 day−1).
The impact of the crayfish Orconectes virilis on aquatic macrophytes
Authors: CHAMBERS PATRICIA A. , HANSON JOHN MARK , BURKE JANICE M. , PREPAS ELLIE E.
Published: May 2006

SUMMARY. 1. The impact of crayfish on the biomass, density and shoot morphology of four submersed plant species was examined under semi‐natural conditions. Male or female crayfish (Orconectes virilis) were held for 5 weeks at biomasses of 0, 5, 10 or 18 g m−2 (live weight) in twelve plastic pools (4.67 m2, surface area) containing Potamogeton richardsonii, Myriophyllum exalbescens, Nuphar variegatum and Sparganium eurycarpum.

2. Crayfish significantly affected biomass, density and/or shoot morphology of all four macrophyte species. Differences in the effect of crayfish on macrophyte growth were related to plant species, crayfish sex and activity, and the abundance of alternative foods.

3. The effect of female crayfish on macrophyte growth was generally stimulatory. Myriophyllum and Potamogeton biomass, Potamogeton density and Myriophyllum length increased in the presence of female crayfish, possibly due to the reduction in herbivorous snails as a result of crayfish predation. In contrast, plant growth decreased in the presence of male crayfish: Myriophyllum, Nuphar and Potamogeton biomass, Myriophyllum and Sparganium density, and Sparganium and Poiamogeton length were reduced at male crayfish biomasses between 5 and 18 g m−2.

4. These results indicate that even relatively low densities of crayfish can greatly affect the growth of submersed aquatic plants. Because of their ability to modify aquatic macrophyte, macroinvertebrate and, ultimately, fish communities, the introduction of crayfish into lakes where they do not occur could have a major effect on the structure and composition of the littoral zone.
The realized food niches of three species of stream‐dwelling triclads (Turbellaria)
Authors: ARMITAGE M. J. , YOUNG J. O.
Published: May 2006

SUMMARY. 1. The diet of Phagocata vitta, Crenobia alpina and Polycelis felina in a Welsh stream was examined, using a serologicat technique, at monthly intervals over 18 months.

2. For each triclad species, dietary composition changed little with time or increasing body size, and overall feeding intensity was greatest in summer and least in winter.

3. Alt species fed most heavily on oligochaetes, chironomids and Gammarus. Phagocata vitta fed lightly on Plecoptera, Trichoptera and Ephemeroptera whilst the other two triclad species fed substantially on the first two of these prey categories.

4. Food niche breadth indices indicated a wide diet for all species with some specialization in some months. Electivity indices showed positive electivity for oligochaetes and chironomids by all species and for Plecoptera by C. alpina and P. felina.

5. Diets overlapped and none had a food refuge: therefore the potential for interspecific competition for food exists.
The ecology of two intermittent streams in Victoria, Australia. I. Multivariate analyses of physicochemical features
Authors: BOULTON A. J. , LAKE P. S.
Published: May 2006

SUMMARY. 1. Amplitudes in physicochemical features in intermittent streams exceed those in nearby permanent streams and strongly influence macroinvertebrate community structure. Hitherto, seasonal variation in the physicochemistry of intermittent streams has been described only anecdotally; there has been no objective attempt to describe phases of flow that could subsequently be compared with patterns in biotic composition.

2. Multivariate techniques of ordination and classification were applied to environmental data collected from pools and riffles at four sites on two intermittent streams in central Victoria during a drought year followed by a wetter year. A cyclical sequence of How phases was usually evident in poo and riffle habitats at all sites over both years: pre‐flow, early flow, main flow, diminishing flow and post‐flow. Several spates that occurred during the sampling period only briefly distorted the cyclical pattern.

3. No single variable characterized these phases at each site; instead, the phases represented complex combinations of discharge, current velocity, dissolved oxygen, conductivity, water temperature and time‐related variables. This highlights the advantages of an integrative, multivariate approach to seek patterns in environmental data, especially since physicochemical features are often highly inter‐correlated.
Modelling black fly production dynamics in blackwater streams
Authors: BENKE ARTHUR C. , PARSONS KEITH A.
Published: May 2006

SUMMARY. 1. Two predictive models were employed along with intensive field sampling to estimate production of black flies (Simulium spp.) on snags (submerged wood) in three blackwater streams on the Georgia Coastal Plain of the southeastern U.S.A. One model predicts daily growth rate from temperature and hydrograph pattern; the other predicts habitat abundance (of snags) from river height.

2. In the sixth order Ogeechee River, annual production was twice as high in 1982 (7.1 g dry mass [=DM] m−2 of snag surface) as in 1983 (3.6 g DM m−2). When converted to production per m2 of river bottom, values were 35–40% of the snag surface estimates. Annual production was much lower in fourth order Black Creek (1982, 1.3 g DM m−2 of snag surface) and much higher in the sixth order Satilla River (1975, 15.6–40.0 g DM m−2).

3. There was a distinct bimodal pattern of black fly production in the Ogeechee River in both years, with peaks occurring in winter and summer. Similar bimodal patterns of production were found in Black Creek and in the Satilla River. Although there appears to be an intrinsic component to the bimodal pattern, production peaks (growth rate and biomass) appear to be associated with initial stages of flooding.

4. Annual production/biomass ratios (37–85) are the highest reported for black fly populations. The variation of annual P/B ratios among sites was more strongly dependent on the temporal distribution of standing stock biomass than on differences in growth rates. Variation in production among sites appears to be due to differences in current velocity, hydro‐graph variability, and abundance of coexisting consumers.
Stonefly predation along a hydraulic gradient: a field test of the harsh—benign hypothesis
Authors: PECKARSKY BARBARA L. , HORN STEVEN C. , STATZNER BERNHARD
Published: May 2006

SUMMARY. 1. Microhabitat preferences of predatory stoneflies and four prey taxa were assessed by taking benthic samples along a hydraulic gradient in a Black Forest stream in West Germany. Densities of predator and prey species were estimated at twenty‐one hydraulic regimes.

2. Enclosures containing the stonefly, Dinocras cephalotes, and control cages with no predators were placed in the substrate at hydraulic regimes favourable and unfavourable to predators. Cages received initial prey communities that were obtained from benthic samples taken at hydraulic regimes matching those intended for each cage.

3. Population densities of the two most numerically important prey taxa, the mayfly. Baetis rhodani, and the Chironomidae, were reduced in the presence of Dinocras, but only when enclosures were placed in the hydraulic regimes favourable to the predator. Thus, predation effects increased as the hydraulic regime became more benign to the predators.

4. Densities of two other prey species rare in the diets of Dinocras (Hydropsyche instabilis and Gammarus fossarum) were generally unaffected by predators regardless of the hydraulic regime.

5. These data provide support for the hypothesis that perception of the abiotic regime as harsh or benign to predators is a good predictor of predator impact on densities of preferred prey species. In harsher abiotic regimes, impact will be low, while impact will be high in benign abiotic regimes.
Photosynthate partitioning in Antarctic freshwater phytoplankton: in situ incubations
Authors: HAWES IAN
Published: May 2006

SUMMARY. 1. The distribution of 14C‐labelled photosynthate by phytoplankton in Sombre Lake, Antarctica, was measured during the spring/ summer period in 1987–88.

2. Protein was the principal product of low‐light photosynthesis, with the proportion of polysaccharide and lipid increasing at higher radiation fluxes. Storage polysaccharides were mobilized during darkness to fuel continued protein synthesis.

3. Maximum rates of protein synthesis and total photosynthesis were attained immediately prior to loss of ice cover, when algal biomass (as chlorophyll‐a) was decreasing. Minimum rale of protein synthesis was coincident with maximum biomass.

4. An increase in loss rates as the growing season progresses is postulated to explain the lack of coupling between biomass changes and photosynthesis.
Zooplankton distribution in relation to turbidity and related environmental gradients in a large subtropical reservoir: patterns and implications
Authors: HART R. C.
Published: May 2006

SUMMARY.

 A marked gradient in water transparency along the 75 km longitudinal axis of Lake le Roux, a fjord‐like reservoir on the Orange River, South Africa, was consistently evident over several years. On average, Secchi depth transparency doubled from approximately 18 cm at the turbid upper end (which is fed by sediment‐laden Orange River water discharged from Lake Verwoerd), to 33 cm near the dam wall. A variety of changes in abiotic limn logical attributes (temperature, light attenuation, suspended solids and nutrient levels, etc.), and in the abundance and composition of planktonic biota accompany, and may be imposed by, this turbidity gradient.

 On average, phytoplankton abundance (assessed as chlorophyll content), and total crustacean zooplankton biomass (per unit volume) were lowest at the very top of the lake, but reached maximal values within 15 km ‘downstream’, reflecting the rapid development of plankton. These variables subsequently declined downstream, in contrast to the apparent improvement in conditions for planktonic existence (increasing water transparency, longer water residence time, etc.).

 The composition of crustacean zooplankton varied along the length of the reservoir. Both seasonal and inter‐annual differences were evident. On average, however, cladocerans (Daphnia, Moina), despite their r‐selected attributes, were especially sparse in the more turbid, uppermost reaches, where advective effects of river inflows were most pronounced. The large predatory copepod Lovenula was surprisingly most abundant in this region, where potential planktonic curstacean prey was scarce. The attainment of maximal zooplankton standing slocks some 15 km downstream was attributable to the proliferation particularly of the herbivorous copepod Metadiaptomus, along with minor increases in several ctadoceran components. The latter continued to increase downstream, in line with declining turbidity, although Daphnia and Moina reached their respective abundance maxima in central and lower reaches of the reservoir, reflecting slight disparities in response to turbidity or related gradients. By contrast.
Quantifying the impact of periphytic algae on nutrient availability for phytoplankton
Authors: HANSSON LARS‐ANDERS
Published: May 2006

SUMMARY.

 Recent laboratory studies demonstrate that periphytic algae growing on the sediment surface reduce nutrient availability in the overlying water. Consequently, periphytic algae may competitively reduce growth of phytoplankton.

 The aim of this study was to quantify the competitive impact of sediment‐attached periphytic algae on phytoplankton in the presence of all other factors simultaneously affecting nutrient dynamics in natural systems.

 In enclosure experiments, performed in three lakes of different productivity, the periphytic algal biomass was manipulated. When compared to enclosures with high biomass of periphytic algae, those with reduced biomass showed an increase in total phosphorus concentration in the water of 32–44%. Extrapolation of the experimental results to whole lakes predicts an increase in original total phosphorus concentration of between 1.5% and 8.0%. According to existing regressions between total phosphorus and phytoplankton chlorophyll, the potential increase in original phytoplankton biomass will be between 2.5% and 12.6%.

 With respect to the shallow parts of lakes, my results support the conclusions revealed from laboratory studies that periphytic algae have a significant impact on the phosphorus concentration in the overlying water. However, when considering whole‐lake dynamics, the competitive impact of periphytic algae on phytoplankton biomass development is probably of minor importance.

 Rather, the main competitive advantage of growing on the sediment surface, compared to in the water, may be the exclusive access to nutrients in the sediment.
Successional changes in the soft‐water macrophyte vegetation of (sub)atlantic, sandy, lowland regions during this century
Authors: ARTS G. H. P. , VAN DER VELDE G. , ROELOFS J. G. M. , VAN SWAAY C. A. M.
Published: May 2006

SUMMARY.

 Considerable changes in macrophyte vegetation can be noticed in 146 originally soft waters, when data on the recent aquatic vegetation are compared with historical information from the period 1900–60. Changes in nutrient status (N, P and C) and accumulation of organic material can be regarded as the operative factors.

 The processes observed in soft waters are acidification, eutrophication and water hardening. Which process dominates depends on the type of soft water.

 Acidification as well as eutrophication of water bodies may ultimately result in the total disappearance of all aquatic macrophytes, with the exception of the floating‐leaved nymphaeids Nymphaea alba L. and Nuphar lutea (L.) Sm. Observed successional stages are described and summarized.
Spatial distribution, seston removal, and potential competitive interactions of the bivalves Corbicula fluminea and Elliptio complanata, in a coastal plain stream
Authors: LEFF LAURA G. , BURCH JARRETT L. , McARTHUR J. VAUN
Published: May 2006

SUMMARY.

 Within the past 10 years the introduced exotic bivalve, Corbicula fluminea, has spread from the Savannah River through a riverine swamp into a third‐order blackwater tributary on the Savannah River Site (SRS). We examined the effects of this invasion on a native bivalve, Elliptio cornplanata, and on seston concentration in the stream.

 Corbicula fluminea has not yet colonized the entire stream and its distribution limit is coincident with the occurrence of gravel beds.

 Corbicula fluminea appears to cause localized reduction of seston concentration and may rapidly clear the sediment boundary layer of food. There was no evidence of a negative impact on the distribution of the native bivalve in spite of high measured rates of water clearance by C. fluminea.
Secondary production of chironomid communities in insecticide‐treated and untreated headwater streams
Authors: LUGTHART GARRIT J. , WALLACE J. BRUCE , HURYN ALEXANDER D.
Published: May 2006

SUMMARY.

 Production of chironomid communities of three first order, Appalachian Mountain streams was estimated and the effects of an insecticide‐induced disturbance on chironomid production was examined.

 Annual production of non‐Tanypodinae chironomids in the streams during the first study year (no treatment) ranged from 1366 to 3636 mg m−2, while production of Tanypodinae chironomids ranged from 48 to 116 mg m −2. Production/biomass ratios ranged between 19 and 23 for non‐Tanypodinae and from 6 to 7 for Tanypodinae chironomids.

 Insecticide applications resulted in significantly lower chironomid densities and biomass in the treated stream relative to the pretreatment year and reference stream. Annual production of non‐Tanypodinae (703 mg m−2) and Tanypodinae (32 mg m −2) chironomids in the treated stream decreased by 64% and 67%, respectively, compared with the pretreatment year. In contrast, production of non‐Tanypodinae (2084 mg m−2) increased by 34% and production of Tanypodinae (96 mg m−2) by 57% in the reference stream.
Effect of predatory fish presence on habitat use and diel movement of the stream amphipod, Gammarus minus
Authors: HOLOMUZKI JOSEPH R. , HOYLE JOHN D.
Published: May 2006

SUMMARY.

 We examined how the presence of predatory fish affected macro—and microhabitat use and movement patterns of the amphipod, Gammarus minus Say, in a second order stream.

 Among macrohabitats, amphipods were consistently more abundant in runs than in pools. Densities in pools were low regardless of fish presence, whereas low densities in runs were correlated with fish presence. Siltation and the lack of coarse substrate particles probably accounted for the scarcity of G. minus in pools. Among microhabitats, G. minus was more abundant in leaf litter and gravel than in silt/sand substrates. Fish presence did not affect microhabitat use in the field. Laboratory manipulations showed, however, that predation rates by green sunfish (Lepomis cyanellus Rafinesque) were significantly lower on amphipods in leaf litter than in other microhabitats.

 Most movement by G. minus in runs occurred at night and was directed downstream. In the laboratory, amphipods significantly reduced swimming activity at night in response to water conditioned with green sunfish. In the field, however, amphipods were only slightly less active in runs at night when exposed to chemical cues of confined green sunfish. The distribution of amphipods in streams is influenced by the presence of fish, but chemical cues alone may not be important in triggering predator avoidance behaviours in nature.
Effect of Anabaena flos‐aquae on the abilities of Daphnia and Keratella to feed and reproduce on unicellular algae
Authors: GILBERT JOHN J. , DURAND MARK W.
Published: May 2006

SUMMARY.

 This study tests the hypothesis that the filamentous cyanobacterium, Anabaena flos‐aquae, inhibits Daphnia's ability to feed and reproduce on unicellular algae more than it does Keratella's. Double‐label radiotracer experiments using whole and sonieally disrupted Anabaena filaments showed that even low concentrations of Anabaena (5 × 103 cells ml−1) inhibited the abilities of Daphnia pulex and D. galeata mendotae to feed on Chlamydomonas and that this inhibition was due to both mechanical interference with feeding and increased food availability. A single‐label radiotracer experiment showed that Anabaena (5 × 103 and 2 × 104 cells ml−l) reduced the abilities of neonate, juvenile, and adult D. pulex to feed on Chlamydomonas but had a much more pronounced effect on adults.

 Single‐label radiotracer experiments using screened (25 μm mesh) and unscreened suspensions of whole Anabaena filaments showed that only very high concentrations of Anabaena (105 cells ml−1) reduced the ability of Keratella cochlearis to feed on Cryptomonas and that this inhibition probably was due to mechanical interference with feeding, since Keratella ate Anabaena extremely inefficiently ‐ especially when single cells and short filaments were removed by screening.

 Experiments comparing the survivorship and fecundity of individuals fed Anabaena, Chlamydomonas, or no food showed that the Anabaena was not toxic to either Keratella or D. galeata mendotae, was not utilized by Keratella, and was utilized by Daphnia, although not as well as Chlamydomonas was.

 Anabaena (5 × 103 or 104 cells ml−1) did not affect, or slightly increased, the population growth rate (rm) of K. cochlearis on Cryptomonas, while it substantially increased that of D. pulex, Duphnia's ability to utilize Anabaena probably more than offset its reduced ability to feed on Cryptomonas. The presence of cyanobacterial filaments in natural plankton communities could adversely affect Daphnia and decrease its ability to competitively suppress Keratella and other rotifers if the filaments were of little nutritional value to the Daphnia, greatly interfered
Genetic variation and reproductive mode in populations of Simocephalus vetulus (Branchiopoda: Cladocera) from the East Midlands of England
Authors: WARD* ROBERT D. , TOLLIT ROSALIND M. , BICKERTON MELANIE A.
Published: May 2006

SUMMARY.
1. Five populations of the cladoceran Simocephalus vetulus (O. F. Muller) examined by enzyme electrophoresis at four to five loci revealed high levels of genetic variation.

2. The one intermittent population had genotype frequencies in Hardy Weinberg equilibrium, the three permanent populations showed deviations from equilibrium of varying magnitude. The fifth population was fixed for a single clone, and was possibly recently derived from a single ephippial hatchling.

3. Laboratory breeding experiments confirmed that this species is a cyclic parthenogen.