bluuebunny/crossref_metadata_2025 huggingface dataset:
The natural regulation of numbers and growth in contrasting populations of brown trout, Salmo trutta, in two Lake District streams
Authors: ELLIOIT J. M.
Published: May 2006

SUMMARY. 1. This short review summarizes a long‐term investigation of brown trout in two populations that probably represent opposite extremes of life histories in this polymorphic species; Bhick Brows Beck serves as a nursery for the progeny of migratory trout (mixture of sea and estuarine trout) and Wilfin Beck is populated by resident trout.

2. Population density in Black Brows Beck was always much higher than that in Wilfin Beck, and was regulated by density‐dependent survival in the early stages of the life cycle. There was no evidence for similar density‐dependent regulation in Wilfin Beck; simple proportionate survival occurred with fairly constant loss‐rates. Survival was reduced in both populations by summer droughts and also by spates in Wilfin Beck.

3. Black Brows trout were always larger than Wilfin Beck trout of similar age; fry size at the start of the growth period was chiefly responsible for these differences. Variations in water temperature were chiefly responsible for differences in growth rates between year‐classes within each population. Food intake was not a limiting factor, except in the first winter of the life cycle and for adults over 3 years old in Wilfin Beck. Variation in individual size was inversely density‐dependent in Black Brows Beck and decreased with age in Wilfin Beck, these changes being due to natural (stabilizing) selection.

4. There is strong evidence for genotypic differences between the populations. The implications of this are discussed, especially the need to conserve different populations that may contain unique genetic material, and the importance of restocking with fish reared from the indigenous population that should always contain the optimum genotypes for a particular habitat. Restocking with juveniles should be done with caution because it could lead to a decrease in both numbers and size variation when the population is regulated by density‐dependent mechanisms.

5. One major objective of future work should be the development and improvement of mathematical models that can be used to predict the optimum density for trout in different populations, the maximum attainable growth rate in different habitats, and the effects on trout populations of environmental changes due to natural causes (e.g. droughts and spates) or human activities.
The ecology of brown trout Salmo trutta in English chalk streams
Authors: MANN R. H. K. , BLACKBURN J. H. , BEAUMONT W. R. C.
Published: May 2006

SUMMARY. .1. Chalkstream trout are fast‐growing, short‐lived with a stable age structure that is a consequence of the lack of extremes in the abiotic environment, especially of water temperature and flow.

2. Levels of secondary (invertebrate) production arc high and there is no evidence that interspecific or intraspecific competition for food resources limits growth.

3. Dietary studies show a broad similarity between trout and other species, but indicate differences that reflect variations in the micro‐habitat distributions between fish species.

4. Trout numbers appear to be limited initially by the availability of gravel spawning areas, and then by areas suitable for newly‐emerged fry. Reduction in stream discharge in the spring, either naturally or by man, can lower the number of 0+ trout that survive.

5. Eels are not important predators on trout eggs or fry. but a reduction in pike numbers can lead to a decrease in the mean weight of pike. Small pike do not pose a serious threat to stocked yearling trout.
Lake restoration by reducing external phosphorus loading: the influence of sediment phosphorus release
Authors: MARSDEN MARTIN W.
Published: May 2006

SUMMARY. 1. This review considers the factors which determine the recovery of eutrophic lakes following a reduction in the external phosphorus loading.

2 The mean phosphorus content of a lake should decrease roughly in proportion to the reduction in phosphorus input. Where the lake phosphorus concentration does not decrease as predicted, then the release of phosphorus from the sediment is implicated.

3. The current understanding of the processes by which sediment phosphorus is mobilized and transported into the photic zone is described. The extent to which phosphorus release can maintain lake phosphorus concentrations following the reduction in external loading is influenced by: lake morphometry, flushing rate, sediment type, trophic state and history of enrichment.

4. A reduction in the phytoplankton biomass of a lake is dependent upon the size of the decrease in lake phosphorus concentration and the degree to which phosphorus limits primary production. The importance of phosphorus in limiting phytoplankton production tends to decrease with increasing lake trophic status.

5. Improvements in the condition of highly eutrophic lakes require very large reductions in external phosphorus loading, whereas in mildly enriched lakes moderate changes in the supply of phosphorus have noticeable effects on phytoplankton biomass.
Culture techniques for studies on the growth, development and reproduction of copepods and cladocerans under laboratory and in situ conditions: a review
Authors: VIJVERBERG J.
Published: May 2006

SUMMARY. This review deals with culture techniques in use to estimate individual growth, development and reproduction of copepods and cladocerans in cultures. The conceptual aspects of growth, reproduction and feeding behaviour are briefly summarized. Marine copepods are included, because the techniques employed for the cultivation of these animals are often more advanced than those used for freshwater crustaceans. Most of the studies reviewed here were carried out under defined laboratory conditions, but a few were under field conditions, generally in small in situ enclosures. The culture methods described in this review are based on 272 studies published between 1910 and 1987. A large number of different culture systems are critically discussed in relation to culture conditions and culture techniques and the taxa used. Particular attention is given to the effect of food quality, and the problem of how to apply laboratory measurements to field populations so as to limit errors to the minimum. A more detailed summary is given in the section on ‘Recommendations’ at the end of the review.
The abundance and temporal distribution of caddisflies (Insecta: Trichoptera) caught by light traps on the Austrian Danube from 1986 to 1987
Authors: WAR1NGER J. A.
Published: May 2006

SUMMARY. 1. Adult Trichoptera were caught for 1 year (May 1986 to June 1987) on the banks of the Danube at Altenwörth, Lower Austria, using a set of three Jermy‐type light traps. From a total of 62,693 specimens caught, the most abundant species were Brachycentrus subnubilus Curtis (Brachycentridae), the two hydropsychids Hydropsyche bulgaromanorum Mal. and Hydropsyche contubernalis McL., Tinodes waeneri L. (Psychomyidae) and the leptocerid Ceraclea dissimilis Steph.

2. The total catch included sixty‐five of the 278 Austrian species from thirteen families. Hydroptila pulchricornis Pictet and Oecetis notata Ramb. were new to the Austrian fauna.

3.Of the meteorological parameters tested, only air temperature seemed to influence flight activity.

4. Twenty‐four species were studied in detail; Halesus tesselatus Ramb. was the only autumn species, the remainder being summer species. In Tinodes waeneri, the flight period was divided into two well‐defined peaks.

5. Of the total, 49.9% were caught during the first third of the night, 39.1% in the second and 11.0% in the last third.

6. In seventeen species the sex ratio was significantly different from 1:1, and it changed during the night.

7. The indication of water quality by light trap catches of caddisflies is discussed.
Long‐term studies on the Windermere populations of perch (Perca fluviatilis), pike (Esox lucius) and Arctic charr (Salvelinus alpinus)
Authors: MILLS CHRIS A. , HURLEY MARGARET A.
Published: May 2006

SUMMARY. 1, Windermere is a glacial valley lake with two basins separated by shallows and a total area of 14.8 km2. Perch, pike and charr are the dominant fish species and have been studied on a continuous basis for over 45 years.

2. The initial slow‐growing stocks of numerous small perch and moderate numbers of large pike were subjected to a heavy initial fishing pressure that was subsequently relaxed for perch but not for larger (>550 mm) pike. The number of charr in the lake has increased 6–8‐fold during the study, probably due to the sustained reduction in the abundance of the larger pike that heavily predate the autumn spawning race of charr when it enters the shallow littoral areas to spawn.

3. The biomass of perch did not recover from the initial fishery until the late 1950s when strong year‐classes occurred in warm summers. However, it was now composed of larger and faster growing individuals. In 1976, disease killed over 98% of all adult perch in the lake and the subsequent recovery has again been slow.

4. Existing models have explained the variation in perch year‐class strength for the years 1959–74 in terms of adult perch biomass, pike cohort strength and temperature in the year of hatch. A new. more generally applicable model, incorporating a stock‐recruitment expression, gives a better fit to the earlier data, particularly from the North Basin, where there have been periods of extremely low adult biomass.

5. The importance of continuing to extend these long‐term data sets and the scope for future modelling work are discussed.
Convergence of insular dwarfism in damselflies (Euphaea) and dobsonflies (Protohermes)
Authors: HAYASHI FUMIO
Published: May 2006

SUMMARY. 1. The life history was compared between mainland and island congeners of Protohermes (Megaloptera: Corydalidae) and also between those of Euphaea (Odonata: Euphaeidae). Larvae of these genera coexisted in stream riffles, and prey availability for them was assessed to examine the effects on their body size at maturation.

2. Body size of P. costalis on the ‘mainland’. Taiwan, was larger than that of an insular congener, P. sp., on Iriomotc and Ishigaki Islands about 200 km east from Taiwan. Insular dwarfism also occurred between E. formosa on the mainland and E. yayeyamana on the islands. All species had an annual life cycle.

3. Prey availability was much lower in the island streams than in mainland streams throughout the year. Convergence of insular dwarfism in these phylogenetically distant but ecologically similar taxa (both predatory insects) suggested that prey availability is an important factor affecting their body size determination.

4. Seasonal changes in body size occurred within a population of Euphaea which lacked synchronous emergence. Adults emerging from larvae spending their late instars in the warm season were smaller than those in the cold season. However, the size differences between species always exceeded the range of such intraspecific variation.

5. Dwarfism in E. yayeyamana was probably achieved by decreasing the size of first‐instar larvae without changing the number of instars and with the size ratio at each moult constant. The mechanisms producing the dwarf form of Protohermes are also discussed.
Evidence of induced plant defences in a pondweed
Authors: JEFFRIES M.
Published: May 2006

SUMMARY. 1. Palatability changes, induced by herbivore damage, have received much attention in terrestrial plant‐insect research but negligible investigation in freshwater systems.

2. Potamogeton coloratus (Potamogetonaceae) and the folivorous caddis larva Triaenodes bicolor (Insecta: Trichoptera) were used to duplicate bioassay techniques common in terrestrial plant‐insect research.

3. Leaves of P. coloratus were artificially damaged. Grazing on damaged leaves, and undamaged leaves from damaged plants, was compared to that on control leaves from undamaged plants up to 10 days after initial damage.

4. The palatability of damaged and undamaged leaves from damaged plants declined compared to control leaves. The differences were significant at 5 days after damage, but had recovered to approximately equal palatability after 10 days.
Prey detection by the water miteUnionicola crassipes(Acari: Unionicolidae)
Authors: PROCTOR HEATHER C. , PRITCHARD GORDON
Published: May 2006

SUMMARY.1. The importance of different senses in prey detection by the common water miteUnionicola carssipeswas investigated.

2. Mechanoreception is likely to be the most important mode of detection; mites preferentially attacked vibrating over non‐vibrating glass probes. The net‐stance, a characteristic posture in which the mite raises its first two sets of legs from the substrate and orients toward vibrations in the water column, is assumed byU. crassipeswhen hunting.

3. Chemoreception may have a role in area‐restricted search: mites exposed to prey‐conditioned water were more sedentary than those exposed to unconditioned water. For a sit‐and‐wait predator likeU. crassipes, remaining still in an area that contains prey will result in a greater predator/prey encounter rate. It is possible that contact chemoreception is used to determine the palatability of an already captured prey item, but mites did not attempt to capture prey they had touched unless the prey moved.

4. Vision is not necessary for prey capture; however, mites captured more prey in the light than in the dark. It is not clear whether this is because vision plays a part in prey detection or because prey behave differently in the two situations.
Structural, physical and chemical characteristics of Microcystis aeruginosa hyperscums from a hypertrophic lake
Authors: ZOHARY TAMAR , MADEIRA ARCANGELA M. PAIS
Published: May 2006

SUMMARY. 1. This paper examines the structural, physical and chemical characteristics of cyanobacterial hyperscums (floating scums of densely packed eyanobacteria. measuring decimetres in thickness, that are covered by a dry crust of photo‐oxidized cells) from hypertrophic Hartbeespoort Dam, South Africa.

2. The hyperscum community was a cyanobacterial‐baclcrial association, in which the cyanobacterium Microcystis aeruginosa comprised 98% of the biovolumc, with cell concentrations exceeding 109 ml−1.

3. The buoyancy mechanism of M. aeruginosa and evaporation at the surface led to increasing compaction of the colonies with declining distance from the surface, and the formation of three distinct, but continuous layers: a 1–2 mm dry surface crust (water content: 14%, chlorophyll a concentration: 3 g l−1), a 5–10 mm compact layer just below the crust (77% water, 1 g l−1 chlorophyll a), and a less compact layer (96% water, 200–500 mg l−1 chlorophyll a) from about 1 cm depth to the bottom, comprising the bulk of the hyperscum.

4. The crust attenuated all the incident light and reduced free gas exchange. Beneath it continuously dark anaerobic, highly reduced conditions prevailed. As the hyperscum aged over 3 months in 1984, at 10 cm depth the pH gradually declined from 6.6 to 5.9, interstitial water ammonia‐N concentrations increased from 0.45 to 119 mg l−1, soluble reactive phosphorus from 2.8 to 83.3 mg l−1, and dissolved organic carbon reached a maximum of 460 mg l−1. At any point in time these concentrations declined gradually with increasing depth within the hyperscum, and declined dramatically beneath the hyperscum. Similar patterns were recorded in another hyperscum in 1986.

5. The chemical and temperature depth profiles indicated that free water movement took place around and under the hyperscum, but within it water movement was restricted to diffusion.

6. Gas bubbles composed of 28% methane. 19% CO2, 53% N2, and traces of H2 trapped within the hyperscum, and the presence of volatile fatty acids in the interstitial water were indicative of anaerobic decomposition processes mediated by fermenting and methanogenic bacteria, and N:P ratios below 1.5 in the interstitial water suggested that nitrogen was lost as gas, possibly through denitrification.

7. We hypothesize that the major sites of decay of M. aeruginosa were the crust and the compact layer beneath it, while deeper within the hyperscum this cyanobacterium could survive prolonged periods of dark anaerobic conditions. This hypothesis requires confirmation.
Refuge availability: a key to understanding the summer disappearance of Daphnia
Authors: WRIGHT DAVID , SHAPIRO JOSEPH
Published: May 2006

SUMMARY. 1. The mid‐summer declines of Daphnia species in three small lakes were investigated to examine the relative roles of reduced natality and increased mortality. Reduced natality (assessed by quantifying clutch size, lipid index, and available food) could not account for the decline in daphnid abundance in any of the populations examined.

2. The role of increased mortality imposed by zooplanktivorous fish was assessed by estimating the sizes of the mid‐water refuge areas where daphnids could escape fish predation. The boundaries of the refuge areas were estimated from field measurements and literature values and were based on gradients of temperature, dissolved oxygen and light. Observed decreases in refuge thicknesses correlated well with the mid‐summer declines of large‐bodied Daphnia species in all three lakes. Intermediatesized daphnids were less affected as the refuges thinned and small‐bodied species increased in abundance.

3. The importance of refuge thickness in modifying zooplanktivore‐induced mortality was further tested in large enclosures where refuge thickness was experimentally modified. In the presence of zooplanktivorous fish, large‐bodied Daphnia, which used the refuge, persisted when the refuge was thick but disappeared when it thinned. Daphnia galeata mendotae, which did not occupy the refuge zone, was rapidly eliminated regardless of refuge thickness. We conclude that refuge availability plays a major role in Daphnia population dynamics.
Forests and the temperature of upland streams in Wales: a modelling exploration of the biological effects
Authors: WEATHERLEY N. S. , ORMEROD S. J.
Published: May 2006

SUMMARY. 1. Daily temperature data from six streams in upland Wales were used to explore the thermal effects of afforestation on stream ecology. The data were linked to published biological models to simulate fish and invertebrate development.

2. Mean daily temperatures in forest streams were lower than those of moorland streams in spring and summer, and higher in winter. These spatial comparisons were supported by the results of experimental bank‐side clearance at a forest site, where there was evidence that stream temperatures fell in winter and rose in spring following treatment.

3. Simulations indicated that brown trout (Salmo trutta) could weigh over 30% more by the end of their second growing season in a moorland compared with a forest stream. Several species of insects showed slower simulated egg development at forest sites. For two ephemeropteran species simulated nymphal growth was also retarded, suggesting significant alterations to the life cycle. Two plecopteran species were affected only slightly by the different temperature regimes.

4. Overall, the simulations suggested that afforestation, by reducing summer temperatures, could lead to marked reductions in rates of development of some invertebrates and fish.
The turbulent boundary between water science and water management
Authors: CULLEN PETER
Published: May 2006

SUMMARY. 1. It is common to observe friction between limnologists and the managers of water resources. This is often a result of misunderstandings about the cultures within which each works.

2. There are a number of ways that science can contribute to effective management of water resources, but limnologists must appreciate that there are value questions which are not the sole prerogative of science to answer.

3. Managers often misunderstand science and expect it to deliver a truth that is non‐arguable. They fail to understand the very process of science demands no such truths, so that assumptions, methods and conclusions can always be challenged.

4. One way to bridge this boundary is to develop the scientific broking role. Another is to do better and more relevant science. Ways of doing both are discussed.
Toxicity of a soluble peptide from Microcystis sp. to zooplankton and fish
Authors: PEÑALOZA R. , ROJAS M. , VILA I. , ZAMBRANO F.
Published: May 2006

SUMMARY.

 A soluble cell fraction lethal to Daphnia magna was isolated by the disruption of net phytoplankton from eutrophic Aculeo Lake. The phytoplankton of this lake is dominated by Microcystis sp.

 The soluble fraction was also lethal to common native zooplankton, including the rotifers Keratella sp., Trichocerca similis, the copepod Boeckella sp., and the cladoceran Chydorus sphaericus. In addition, a partially purified soluble component of the lethal fraction caused the death of the fish Gambusia affinis.

 The specific toxicity of the soluble fraction from phytoptankton varied four‐ to six‐fold seasonally with peaks during periods of warm temperature.

 Our results suggest that releases of a toxic peptide from Microcystis sp. may be the cause of massive fish kills at the study site, Aculeo Lake.
Species distributions and shell characteristics of Pisidium (Mollusca: Bivalvia) in the Colorado Front Range: the role of abiotic factors
Authors: SAUNDERS JAMES F. , RUNG GEORGE W.
Published: May 2006

SUMMARY.

 Forty lakes in the Colorado Front Range were sampled to examine the relationship between water chemistry and the distributions and shell characteristics of Pisidium species. Alkalinity, pH, and dissolved organic carbon contributed most to the classification of lakes according to the dominant Pisidium species. Alkalinity was also strongly correlated with mean clam weight for populations of P. casertanum, the most common of the five species collected.

 Historical evidence shows a reduction in the number of lakes occupied by clams and a constriction in the distributions of certain species. These changes have occurred mainly in lakes that now have low alkalinity.

 A role for acidification is suggested because the recorded changes in distributions have occurred during the last 20 years, coincident with a general decline in alkalinity in waters of the Front Range.
A quantitative study of mortality at emergence in the damselfly Pyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae)
Authors: GRIBBIN SIMON D. , THOMPSON DAVJD J.
Published: May 2006

SUMMARY.

 Emergence of the damselfly Pyrrhosoma nymphula was studied over three seasons in two ponds in northern England.

 Numbers emerging were significantly negatively correlated with temperature and atmospheric pressure.

 Overall mortality at emergence was 28%. of which predators (largely birds, ants and spiders) accounted for 22% and climatic factors 6%.

 Daily mortality estimates were significantly positively correlated with precipitation.

 There was no evidence of density dependent mortality at emergence.
The food and daily food consumption of lacustrine 0+ perch, Perca fluviatilis L.
Authors: TREASURER JAMES W.
Published: May 2006

SUMMARY.

 The diet and daily food consumption (Ct) of 0+ perch were investigated in two shallow Scottish lakes.

 The first food comprised the rotifer Keratella sp., Volvox sp., copepod nauplii and stage I copepodites of Cyclops strenuus abyssorum Sars. Larger copepodites and adults of C. s. abyssorum and Diaptomus gracilis Sars were consumed as larvae grew and cladocerans were also eaten by larvae >11 mm. The diet of juveniles included a wider range of cladocerans and benthic invertebrates. Cannibalism was not observed among 0+ perch.

 The range of food items taken by larvae increased with length, and the size of food particles ingested was governed by jaw gape which was linearly related to fish length.

 Larvae fed during daylight hours with feeding maxima in midmorning and the evening.

 The arithmetic (constant) rate of evacuation R of the digestive tract of larvae was 0.59—1.16% of body weight h−1 and exponential R was 0.21–0.33% h−1. Daily Ct calculated using an arithmetic model was 14.2–23.4% body weight at water temperatures of 12.5–18.2°C, and 23.9–40.3% utilizing an exponential method. For larvae of 9 mm. this was 46 μg dry weight day−1 and 148 by an exponential model. Food conversion efficiency was 37–72% (arithmetic model) and 21–45% (exponential model).
Macroinvertebrate size‐distributions of two contrasting freshwater macrophyte communities
Authors: HANSON JOHN MARK
Published: May 2006

SUMMARY.

 Macroinvertebrates (>0.1 mg, fresh weight) were collected every 2 weeks for 18 weeks from weedbeds dominated by either the macroalga Chara or rooted plants (mostly Isoetes sp., Potamogeton filiformis, Nuphar variegatum and Myriophyllum exalbescens) in Narrow Lake, Alberta, Canada. Significant differences in total biomass, taxonomic composition, and size‐structure of the macroinvertebrate community were found between the two weedbed types.

 Total biomass of macroinvertebrates in the Chara beds (seasonal mean 26.4 g m−2) was consistently higher than in the rooted‐plant weedbeds (seasonal mean 7.6 g m−2).

 The macroinvertebrate community of the Chara beds was dominated by chironomids, anisopterans, gastropods and sphaerid clams whereas amphipods dominated the community in the rooted‐plant weedbeds.

 On average, the proportion of total biomass in the various size‐classes (biomass size‐spectrum) of the macroinvertebrate community in Chara beds varied very little between 1 and 512 mg. In rooted plant weedbeds, the spectrum showed a strong peak in the 4–8 mg size‐class, a weak peak in the 32–64 mg size‐class, and proportionately low biomass in the 128–256 mg and 256–512 mg size‐classes. The slope of the normalized size‐spectrum for the macroinvertebrate community of the Chara beds (‐0.89) was significantly different from that of the rooted plant community (‐1.11). The biomass of large organisms (>64 mg) was 10 times greater in the Chara beds than in the rooted‐plant weedbeds.

 The species composition of aquatic macrophyte beds can greatly influence the abundance, taxonomic composition, and size‐structure of the littoral zone macroinvertebrate community. Therefore, any changes in plant species composition of weedbeds, through introduction of exotic plant species or introduction (or loss) of an efficient grazer (e.g. crayfish), have the potential to alter greatly the structure of the macroinvertebrate community in a lake, with unknown consequences to fish and waterfowl dependent upon these prey.
Indirect effects of fish predation on calcite supersaturation, precipitation and turbidity in a shallow prairie lake
Authors: HANSON MARK A. , BUTLER M. G. , RICHARDSON J. L. , ARNDT J. L.
Published: May 2006

SUMMARY.

 We tracked calcite saturation and seston composition during 1987 and 1988 in a shallow, hardwater prairie lake, 1 year before and 1 year after a lake‐wide fish removal. We also measured the contribution of calcite to turbidity during 1988.

 In both years calcite saturation increased rapidly after all ice had thawed and peaked during mid‐late summer with the mineral saturation index of calcite (SI) sometimes exceeding 30.

 Removal of calcite from lake seston by gentle acidification of unfiltered water samples showed suspended calcite to be an important source of lurbidity in this lake.

 The lake‐wide fish removal produced detectable changes in the annual cycle of calcite saturation and precipitation. Increased grazing by Daphnia galeata and Daphnia pulex apparently reduced calcite saturation during early summer by suppressing the phytoplankton, and lowering the demand for CO2.

 Lower calcite precipitation, as well as direct removal of calcite by Daphnia grazing, probably contributed to the improvement in water transparency observed after the fish kill.
Transported material in a small river with multiple impoundments
Authors: PALMER ROBERT , O'KEEFFE JAY
Published: May 2006

SUMMARY.

 The transport of particulate material in a multiply‐impounded southern African river was studied from source to mouth over a period of 2 years during base flow conditions.

 More than 95% of the dissolved and particulate material in transport was ultra fine (<80 μm). We conclude that too much emphasis has been placed on coarse material (>1 mm) in theories of river ecosystem functioning.

 The ratio of CPOM:FPOM (1000–4000:250–1000 μm) in transport decreased with increasing stream order as a result of inputs of FPOM from pollution sources and from plankton blooms discharged from reservoirs.

 The downstream effects of impoundment depended largely on the type of release and the quality of the inflowing water: surface‐releasing reservoirs in the clean, upper reaches of the river had the least effect on transported material. A polluted surface‐release impoundment in the mid‐reaches of the river converted the particle size spectrum of the river from small (<80 μm) to large (250–1000 μm). Bottom‐released water carried high concentrations (36–190 g m3) of small (<5 μm) and largely inorganic (86–93%) material.

 The distance required for zooplankton densities to reduce by 95% was between 4 and 8 km downstream of an impoundment, except below a polluted impoundment where zooplankton densities took 32–35 km to reduce by 95%.

 Most of the downstream changes in transported organic matter in the Buffalo River are due to inflows of agricultural and urban effluent. These disturbances to the river cause greater perturbations than do the impoundments.
Density—body size allometry does not exist in a chironomid community on Myriophyllum
Authors: TOKESHI MUTSUNORI
Published: May 2006

SUMMARY.

 It has been proposed that population density is allometrically related to body size for a wide range of animal species. An interesting question is whether this applies to species within a specific community or trophic guild, thus constituting a ‘pattern’ of community structure.

 Density‐body size allometry can be translated into the relationship between population biomass (B) and population density (N). If the regression coefficient b in log B = a + b log N approximates 1, there is no allometric relation between density and body size.

 Data from an epiphytic chironomid community show b∼1, thus indicating that no density‐body size allometry exists in this community.

 Biomass is less equitably distributed than numbers among species in this and many other communities.

 There is some difficulty in extending the logic of the density‐body size allometry to many invertebrate communities, where body size is a strongly time‐dependent, variable trait.
Cellulose digestion and metabolism in the freshwater amphipod Gammarus pseudolimnaeus Bousfield
Authors: CHAMIER ANNE‐CAROLE
Published: May 2006

SUMMARY.
1. Weight‐specific respiration and feeding rates of Gammarus pseudolimnaeus were inversely related to body weight at 12°C, the temperature of the stream from which they were collected.

2. At this temperature animals could digest about a third of ingested, purified 14C‐cellulose. In animals greater than 20 mg live weight, about 38% of ingested cellulose was metabolized; animals smaller than 20 mg metabolized about 28%.

3. Respired CO2 from cellulose metabolism was 33–47% of measured uptake of C2 in animals greater than 20 mg live weight and approximately 25% in smaller animals.

4. Ability to digest cellulose would be of nutritional benefit to Gammarus feeding on any plant material, but would be of particular advantage in the spring/summer period when fine detritus is the main foodstuff.
Tolerance and resistance to thermal stress in juvenile Atlantic salmon, Salmo salar
Authors: ELLIOTT J. M.
Published: May 2006

SUMMARY.
1. The chief objective was to construct a thermal tolerance polygon for juvenile Atlantic salmon, Salmo salar L., using fish from four groups and two populations: two age groups from one population (0+, 1+ parr from River Leven), two size groups from the other population (slow and Fast growing 1+ parr from River Lune).

2. Fish were acclimated to constant temperatures of 5, 10, 15, 20, 25 and 27°C; then the temperature was raised or lowered at 1°C h−1 to determine the upper and lower limits for feeding and survival over 10 min, 100 min, 1000 min and 7 days. As they were not significantly different between the four groups of fish, values at each acclimation temperature were pooled to provide arithmetic means (with SE) for the thermal tolerance polygon.

3. Incipient lethal levels (survival over 7 days) defined a tolerance zone within which salmon lived for a considerable time; upper mean incipient values increased with increasing acclimation temperature to reach a maximum of 27.8±0.2°C, lower mean incipient values were below 0°C and were therefore undetermined at acclimation temperatures <20°C but increased at higher acclimation temperatures to 2.2±0.4°C. Resistance to thermal stress outside the tolerance zone was a function of time; the ultimate lethal level (survival for 10 min) increased with acclimation temperature to a maximum of 33°C whilst the minimum value remained close to 0°C. Temperature limits for feeding increased slightly with acclimation temperature to upper and lower mean values of 22.5±0.3°C and 7.0±0.3°C.

4. In spite of different methodologies, values in the present investigation are similar to those obtained in previous, less comprehensive studies in the laboratory. They also agree with field observations on the temperature limits for feeding and survival. Thermal tolerance polygons are now available for eight species of salmonids and show that the highest temperature limits for feeding and survival are those recorded for juvenile Atlantic salmon.
Lethal and sub‐lethal effects of acid, aluminium and lime onGammarus pulexduring repeated simulated episodes in a Welsh stream
Authors: McCAHON C. PETER , POULTON MADELINE J.
Published: May 2006

SUMMARY.1. A soft‐water stream in upland mid‐Wales was dosed with sulphuric acid, aluminium sulphate and limestone slurry to produce a zone of aluminium at low pH. and one of aluminium, low pH and added lime.

2. Three episodes of 24‐h duration were induced, each separated by a 12‐h inter‐dosing period, and the responses of the crustaceanGammarus pulexmonitored throughout.

3.G. pulexparasitized by the acanthocephalanPomphorhynchus laeviswere significantly more sensitive than unparasitized individuals.

4. Liming significantly reduced mortality during dosing but postexposure deaths were greatest for animals which had been exposed in the time zone.

5. The disruption of precopulalory behaviour inG. pulexwas rapid and liming did not mitigate this response.
Rates of gastric evacuation in piscivorous brown trout, Salmo trutta
Authors: ELLIOTT J. M.
Published: May 2006

SUMMARY.
1. The dry weight of food remaining in the stomachs of piscivorous trout decreased exponentially with time. Gastric evacuation rates increased exponentially with increasing temperature but were unaffected by predator size, meal size or type of fish prey.

2. Mathematical models were developed to estimate both the rate and time for the gastric evacuation of different meal sizes (expressed as dry weight), and were applicable to piscivorous trout of different sizes (length range 10–32 cm) feeding on trout fry or sticklebacks at different temperatures (range 5–18°C).

3. The wet weight of food in the stomachs also decreased exponentially with time, but evacuation rates both increased with temperature and decreased with increasing meal size; the latter relationship occurred because relative rates of water loss from a meal also decreased with increasing meal size. Use of wet or dry weights can therefore lead to different conclusions about the effect of meal size on evacuation rates.

4. When piscivorous trout were fed three consecutive meals of varying size, the models predicted the total dry weight of food left in the stomach, but not the weight remaining for each individual meal. Interactions between meals led to an increase in evacuation rates for meals consumed early in the series and a decrease in evacuation rates for later meals.

5. Evacuation rates for piscivorous trout were compared with those for trout feeding on invertebrates in an earlier study, and were close to those for caddis larvae as prey, higher than those for mealworms and lower than those for a variety of invertebrate prey. Although a great deal is now known about the daily food intake and growth rates of trout feeding on invertebrates, there is little comparable information for piscivorous trout.
Longitudinal variation in recolonization rates of macroinvertebrates along an upland river in south‐eastern Australia
Authors: MARCHANT R , LAKE P.S. , DOEG T.J.
Published: May 2006

SUMMARY.
1. Recolonization rates of benthic invertebrates were estimated at five sites in the catchment of the Acheron River, in spring (October) and in summer (January), The sites ranged from those that experience short floods and high shear stress at the streambed (upstream sites) to those that experience prolonged floods and low shear stress (downstream sites). We hypothesized that these differences should affect recolonization rate.

2. In October, absolute rates of recolonization of taxa (number of taxa 0.05 m−2 d−1) onto 1‐m2 patches of substratum, which had been raked to remove fauna, did not vary between the three sites studied, nor did the relative rates of recolonization of taxa (absolute rate/mean number of taxa in control samples, which were taken from adjacent undisturbed patches of substratum). Absolute rates of recolonization of individuals (number of individuals 0.05 m−2 d−1) were proportional to the mean number of individuals in control samples; relative rates of recolonization of individuals (absolute rate/mean number of individuals in control samples) did not vary between sites.

3. In January, absolute rates of recolonization either of taxa or individuals were positively correlated with the mean densities of taxa or individuals in control samples; relative rates did not vary between the four sites studied.

4. We conclude that the benthic invertebrate communities at the various sites do not adapt to variations in flooding regime by altering relative recolonization rates. Absolute recolonization rates are directly proportional to the prevailing number of taxa or individuals at a site.
Changes in structure and composition of an assemblage of Hydroporus species (Coleoptera: Dytiscidae) along a pH gradient
Authors: JULIANO STEVEN A.
Published: May 2006

SUMMARY.
1. Patterns of total abundance and species relative abundances in an assemblage of predatory dytiscid beetles of the genus Hydroporus were examined along a pH gradient within a ditch in north‐cast England.

2. During spring, total abundance of adult Hydroporus was greatest at the less acidic (pH 5.6–6.2) upstream sites, whereas total abundance of larval Hydroporus was greatest at the more acidic (pH 4.5) downstream sites. Both adults and larvae were more abundant in samples from the edge than from the middle of the ditch.

3. Species number and evenness did not differ along the pH gradient.

4. Species relative abundance patterns varied along the pH gradient, with particular species dominating at different sites. However, relative abundances of species changed discontinuously along the pH gradient.

5. Comparison of species abundance patterns along this pH gradient with published patterns of presence/absence among bodies of water with different pH revealed that species relationships with pH are often not consistent. Possible sources of this inconsistency are: geographic variation in species' pH preferences; complex responses of individual species to many factors in addition to pH; or random variation among sites due to colonization and extinction history.

6. The overall results suggest that pH is not the only, or even the most important, factor influencing Hydroporus populations and assemblage organization.
Influence of food quality on growth and reproduction in Daphnia
Authors: GROEGER ALAN W. , SCHRAM MARK D. , MARZOLF G. RICHARD
Published: May 2006

SUMMARY.
1. Growth and reproduction were measured for Daphnia pulex (Leydig) fed Scenedesmus obliquus (Turp.) Kutz. grown with nitrogen‐sufficient and nitrogen‐deficient media. The incorporation of carbon into the body of D. pulex was traced using 14C‐labelled algae and biochemical fractionation.

2. Scenedesmus cultured on N‐defkient media allocated more carbon to lipid and less to protein than when cultured on N‐sufficient media.

3. In a short‐term feeding experiment, Daphnia accumulated more lipid when fed N‐deficient algal cells high in lipid content than when fed algae grown on N‐sufficient media that were lower in lipid.

4. Animals grew faster and produced larger broods when fed algae grown on an N‐sufficient medium over an 8‐day period. Daphnids fed N‐deficient algae had higher quantities of body lipid, suggesting it was not a lack of energy which limited their growth and reproduction.

5. Daphnia fed algae grown on N‐deficient media allocated more lipid to eggs, and their offspring lived longer under starvation conditions.
An experimental study of the breakdown of submerged leaves by hyphomycetes and invertebrates in Morocco
Authors: CHERGUI HASSAN , PATTEE ERIC
Published: May 2006

SUMMARY.
1. Mechanisms of the breakdown of submerged leaves under the warm and dry Moroccan climate, including the interaction between hyphomycetes and invertebrates, were investigated.

2. Laboratory experiments were performed on dried leaves of Salix sp. and Nerium oleander.

3. During the first month under the experimental conditions, Melanopsis praemorsa, Physa acula (Gastropoda) and Hydropsyche maroccana (Trichoptera), respectively, were responsible for a loss of weight of 38, 21 and 13% in willow leaves, and 40, 15 and 8% in oleander leaves.

4. The weight lost by willow leaves inoculated with the fungi Alatospora acuminata, Anguillospora longissima, Lemonniera aquatica and Tetracladium marchalianum increased with time, but varied according to the fungal species. Loss of weight and increase in nitrate and phosphate content of the leaves were greatest with Lemonniera and smallest with Tetracladium.

5. When the leaves thus colonized by each of the four fungal species were exposed to each of the three invertebrates, the amount of material consumed increased with the time of fungal conditioning and varied according to the fungus and to the invertebrate. Greatest consumption was by Melanopsis feeding on leaves conditioned by Lemonniera, in which case assimilation percentage by the gastropod was as high as 75%.

6. Owing to their numbers in the field, and to the quantity of leaf material they ingest, gastropods appear as the main shredders in the streams considered, thus replacing the Crustacea that often play this part under temperate climates. Breakdown seems faster in Morocco than in France, mainly because of a shorter initial time lag in weight loss.
Influence of food density on the effects of a Chaoborus‐released chemical on Daphnia ambigua
Authors: HANAZATO TAKAYUKI
Published: May 2006

SUMMARY 1. Daphnia ambigua was reared individually at four different food levels in water conditioned by a predator, Chaoborus flavicans. Daphnia ambigua developed spike‐like helmets during the first four instars in each treatment with the Chaoborus‐conditioned water, but only during the first instar in untreated water. The helmet development at instars 2–4 was probably induced by a chemical released from the Chaoborus.

2. The helmets decreased in size with decreasing food levels, but never ceased to form, even at a very low food concentration.

3. Daphnids cultured in the Chaoboras‐conditioned water exhibited reduced growth, reproduction and survival rates at low food levels. These results might be induced by the energy loss associated with producing the helmets.

4. It is suggested that the predator releases a chemical, which reduces the tolerance of the cyclomorphic Daphnia to food deficiency, thus accentuating the summer decline in the Daphnia population caused by food shortage.
Laboratory studies of egg development and diapause in Isoperla obscura (Plecoptera) from a mountain stream in Norway
Authors: ØKLAND BØRN
Published: May 2006

SUMMARY 1. A laboratory study of egg development of the stonefly Isoperla obscura (Zetterstedt) collected from the stream Flybekken (southern Norway, 61°25'N, 8°48'E, 1373 m a.s.l.) showed a short diapause followed by a prolonged period of postdiapause quiescence.

2. Diapause occurred over a wide range of temperatures (−20°C to +8°C), but 0–1°C was the most favourable for fast diapause development and successful hatching. Diapause development required temperatures below 12°C, but sub‐zero diapause temperatures increased mortality during the postdiapause phase, as well as reducing hatching success.

3. The threshold for initiation of postdiapausal development was about 1–2°C. Development rate increased and variation in development time decreased at higher water temperatures. These may be important characteristics to ensure seasonal and geographical synchrony of development in individual populations. Low postdiapausal temperatures were unfavourable, despite a subsequent increase in water temperature. No response to postdiapausal photoperiod was detected.

4. The results agreed well with conditions noted in the natural environment, and with the abundance of this species at high altitudes and latitudes in Fennoscandia. Nevertheless, Isoperla obscura also occurs in streams in the maritime parts of western Norway. The results of the present study suggest that egg development in these populations will prove to be different.
The effect of the acanthocephalan parasite (Pomphorhynchus laevis) on the drift of its intermediate host (Gammarus pulex)
Authors: McCAHON C. P. , MAUND S. J. , POULTON M. J.
Published: May 2006

SUMMARY 1. The drift of Gammarus pulex in a population in which approximately 20% of adults are infected with the acanthocephalan parasite Pomphorhynchus laevis was monitored at margin and mid‐river sites in the River Teme, England over a 24‐h period in mid‐summer.

2. Drift densities showed a diurnal pattern with a large increase at night, independent of parasite burden.

3. There was no significant effect of site (margin or mid‐river) on the proportion of parasitized and unparasitized G. pulex found in the drift or the benthos.

4. The drift of parasitized G. pulex was significantly greater than unparasitized animals. Gammarids harbouring only one parasite were found in significantly higher proportions in the drift than those with two or more parasites.

5. At both sites (margin and mid‐river) the proportion of unparasitized adult G. pulex in the drift was significantly lower than that in the benthos. However, there was a significantly higher proportion of parasitized animals in the drift than in the benthos.
Spatial distribution of freshwater mussels: the role of host fish and metabolic rate
Authors: BAUER G. , HOCHWALD S. , SILKENAT W.
Published: May 2006

SUMMARY.
1. Three species of the superfamily Unionacea live in Bavarian trout streams: the freshwater pearl mussel Margaritifera margaritifera which usually occurs alone, and the unionids Unio crassus and Anodonta piscinalis which are frequently associated.

2. We found no evidence for competition between M. margaritifera and the unionids. Two types of habitat factors were analysed: (i) the occurrence of host fish, which does not explain the distributional relationships of mussels; and (ii) hydrochemical factors indicating a lower productivity in the rivers inhabited by M. margaritifera.

3. With respect to physiological differences, M. margaritifera is separated from the other two species by low growth constants and low metabolic rates. We conclude, therefore, that the metabolic rate is an important factor governing distribution of the species: M. margaritifera is able to grow in rivers with low food availability, whereas the higher metabolic rates of U. crassus and A. piscinalis presumably necessitate a richer food supply.