bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal allocation of energy to respiration, growth and reproduction in the freshwater clams, Pisidium variabile and P. compressum (Bivalvia: Pisidiidae)
Authors: WAY CARL M.
Published: May 2006

SUMMARY. 1. The ecological energetics of the pisidiid clams, Pisidium variabile and P. compressum, from permanent ponds in southwestern Ohio were studied from July 1978 to July 1980. Productivity (P; as g C m−2 yr −1) was 1.82 (0.80 and 1.02 for the spring and autumn generations) and 4.22 (2.69 and 1.53 for the spring and autumn generations) for P. variabile and P. compressum, respectively.

2. The average biomass (B; as g C m−2) of P. variabile was 0.54 (0.30 and 0.24 for the spring and autumn generations) and of P. compressum 1.09 (0.69 and 0.40 for the spring and autumn generations). P:B ratios for the spring and autumn generations of P. variabile were 2.7 and 4.2 and of P. compressum 3.9 and 3.8, which are below those reported for other iteroparous invertebrates.

3. Reproductive effort (Re:Px100) was 5.1 and 5.7 for the generations of P. variabile and 7.7 and 8.8 for the generations of P. compressum. These low values relative to other molluses can be attributed to a viviparous mode of reproduction and exposure to local environmental variability. In addition, the differences between the reproductive efforts of the spring and autumn generations of both species can be ascribed to season of birth and altometric constraints on reproductive capacity.

4. The data from this and related studies on pisidiid clams are used to generate several hypotheses concerning the evolution of life cycles in the family: (1) reproductive effort is limited by allometric constraints on clam size; (2) individuals of different ages can have different demographies and physiological rate functions; and (3) current one‐dimensional life history theories are largely inappropriate when dealing with an organism that has a wide range of phenotypic responses to environmental variability as well as complex age structure.
Population dynamics and morphometries of Gammarus pulex L.: evidence of seasonal food limitation in a freshwater detritivore
Authors: GEE JOHN H. R.
Published: May 2006

SUMMARY. 1. Seasonal changes in population size structure of Gammarus pulex L. in a Cotswold stream appeared to indicate a growth check in late summer.

2. The relationships between dry weight and body length, and between the number of primary flagellar segments on the first antenna and either dry weight or body length provided further evidence of a reduction in growth in mid and late summer.

3. Body fat content was minimal (4% of dry weight) at the end of summer, when large particulate organic detritus was scarce or of poor quality, and maximal in late winter (17.9% dry weight in females; 9.4% in males), after a period of high food availability. In a field experiment, the fat content of animals in summer was raised to levels typical of winter by providing high quality food.

4. Field and experimental evidence together strongly infer that this population of G. pulex was subject to severe food limitation from early summer until leaf fall in autumn.
Age, growth and reproduction of Aphanius iberus (Cuv. & Val., 1846) in the lower reaches of the Guadalquivir river (south‐west Spain)
Authors: FERNANDEZ‐DELGADO C. , HERNANDO J. A. , HERRERA M. , BELLIDO M.
Published: May 2006

SUMMARY. 1. Age, growth and reproduction in an Atlantic population of the small fish, Aphanius iberus (Cuv. & Val., 1846), from the estuary of the Guadalquivir river were studied.

2. The growth period was from April to September and the annulus on the scales was formed in April.

3. The life‐span was short with a winter age‐structure of 95.9% 0+ fish, 3.9% 1+ and 0.2% 2+.

4. The fecundity of this stock, before the beginning of reproduction, is represented by the formula: Fec=0.907 TL (cm)4.099. During the reproductive period 1+ females contained more, smaller eggs g−1 of gonad than 0+ fish.

5. Males matured before females, but females were larger than males. The overall sex ratio did not differ from 1:1 but males dominated significantly during most of the spawning period.

6. Aphanius iberus spawned intermittently during the reproductive period. From April to July, 1+ group specimens (7–12 months old) reproduced. Their offspring (0+ group; 3–4 months old) reproduced from July to September. Very few of the 1+ group specimens survived to spawn the following year.

7. Mean gonadosomatic indices were much higher in the 1+ group than in the 0+ group and in females compared to males.

8. The loss of condition and the disappearance of the 1 + group during spawning, may indicate the cost of a prolonged high level of reproductive effort.

9. In this productive environment, the life history of Aphanius iberus is similar to that of Gambusia affinis (Baird & Girard, 1853) and Fundulus heteroclitus (Linnaeus) found in the same area.
Grazing on filamentous algae by herbivorous zooplankton
Authors: FULTON ROLLAND S.
Published: May 2006

SUMMARY. 1. Feeding experiments were conducted to examine filtering rates and selectivity of a variety of zooplankton taxa (including cladocerans, copepods and a rotifer) for filamentous diatoms, green and blue‐green algae.

2. Most herbivores were capable of consuming some filamentous algae at rates similar to or higher than those on unicellular algae. Only feeding of Diaphanosoma brachyurum Liéven and Moina micrura Kurz seemed to be primarily limited by the filamentous morphology.

3. Filtering rates and selectivities of most herbivores were much higher for the diatom Melosira granulata angustissima Müller than for similarly sized blue‐green algal filaments, indicating that chemical factors strongly influence consumption of filamentous algae.

4. The toxic blue‐green algal filament Anabaena flos‐aquae De Brébisson NRC 44–1 had a much strong inhibitory effect on zooplankton feeding than other filaments. The only herbivores that were not inhibited by this strain have been shown to be resistant to blue‐green algal toxins, or strongly avoided consuming the blue‐green alga. These results indicate that the inhibitory effect of filamentous algae is due more to toxic or noxious chemicals than to the filamentous morphology.

5. Selectivities of zooplankton for filamentous algae were largely independent of herbivore body size. The small‐bodied cladoceran Bosmina longirostris Müller had the highest selectivities for filamentous algae.
Digestive ability of the freshwater crayfish Paranephrops zealandicus (White) (Parastacidae) and the role of microbial enzymes
Authors: MUSGROVE RICHARD J.
Published: May 2006

SUMMARY. 1 Ingestion rate, assimilation efficiency and digestive enzyme activity were investigated in the New Zealand freshwater crayfish, Paranephrops zealandicus (White). Rates of ingestion of fresh and decaying Elodea canadensis Michx. were highly variable at 15°C and assimilation efficiency averaged 21%.

2.Hepatopancreas extracts showed enzyme activity towards each of nine substrates tested; microcrystalline cellulose (MCC), carboxymethyl cellulose (CMC), cellobiose, amylose, pectin, mannan, laminarin, chitin and‘Azocoll’ (a dye‐collagen complex).

3. Three genera of Enterobacteriacae were isolated from digestive juices and hepatopancreas samples and microbial activity was implicated in the breakdown of MCC, laminarin and protein. Host‐specific activity was not detected in the assays with MCC suggesting a solely microbial source for this enzyme.

4. Although cellulose cannot be broken down without some degree of prior conditioning, the polytrophic feeding strategy of P. zealandicus is indicated by the presence of host‐specific enzymes that hydrolyse storage and structural sugars of algae, fungi and higher plants as well as animal protein.
Distribution of planktonic ciliates in highly coloured subtropical lakes: comparison with clearwater ciliate communities and the contribution of myxotrophic taxa to total autotrophic biomass
Authors: BEAVER JOHN R. , CRISMAN THOMAS L. , BIENERT RAYMOND W.
Published: May 2006

SUMMARY 1. The planktonic ciliate communities of eleven organically coloured north and central Florida lakes representing a variety of trophic conditions were examined during 1979–80. The total abundance and biomass of ciliates were not significantly different from comparable clearwater lakes and only minor taxonomic replacements were noted at the order level.

2. Timing of population peaks of oligotrophic lakes was dissimilar to clearwater lakes of the same trophic state, but seasonality in meso‐trophic and eutrophic lakes resembled patterns described for comparable clearwater lakes.

3. Various ciliate components were strongly correlated with chlorophyll a concentrations, but only moderately correlated to dominant phytoplankton groups. No significant correlations were found between ciliate components and bacterial abundance.

4. Myxotrophic taxa numerically dominated oligotrophic systems, particularly during midsummer, and accounted for a large percentage of the total ciliate biomass. Estimates of the ciliate contribution to total autotrophic biomass indicate that these zoochlorellae‐bearing protozoa may account for much of the autotrophic biomass during midsummer periods in coloured lakes, and thus may lead to an overestimation of phytoplankton standing crops available to zooplankton grazers if chlorophyll a is used as a surrogate measure of algal biomass.
Habitat utilization by sympatric arctic charr Salvelinus alpinus L. and brown trout Salmo trutta L. in Lake Atnsjø, south‐east Norway
Authors: HEGGE OLA , DERVO BØRRE K. , SKURDAL JOSTEIN , HESSEN DAG O.
Published: May 2006

SUMMARY. 1. Habitat utilization, as well as inter‐ and intraspecific relations of different size groups of arctic charr (Salvelinus alpinus (L.)) and brown trout (Salmo trutta L.) in Lake Atnsjø, south‐east Norway, were investigated by analysing food and spatial niches from monthly benthic and pelagic gillnet catches during June‐October 1985.

2. Small individuals (150–230 mm) of both arctic charr and brown trout occurred in shallow benthic habitats. However, they were spatially segregated as arctic charr dominated at depths of 5–15 m and brown trout at depths of 0–5 m.

3. Larger (>230 mm) arctic charr and brown trout coexisted in the pelagic zone. Both species occurred mainly in the uppermost 2‐3 m of the pelagic, except in August, when arctic charr occurred at high densities throughout the 0–12 m depth interval. On this occasion, arctic charr were segregated in depth according to size, with significantly larger fish in the top 6 m. This was probably due to increased intraspecific competition for food.

4. The two species differed in food choice in both habitats, Arctic charr fed almost exclusively on zooplankton, whereas brown trout had a more variable diet, consisting of surface insects, zooplankton. aquatic insects and fish.

5. The data suggest that the uppermost pelagic was the more favourable habitat for both species. Large individuals having high social position occupied this habitat, whereas small individuals lived in benthic habitat where they were less vulnerable to agonistic behaviour from larger individuals and less exposed to predators. The more aggressive and dominant brown trout occupied the more rewarding part of the benthic habitat.
Microhabitat availability in Welsh moorland and forest streams as a determinant of macroinvertebrate distribution
Authors: RUTT G. P. , WEATHERLEY N. S. , ORMEROD S. J.
Published: May 2006

SUMMARY. 1 Eighteen streams in mid‐Wales were sampled for macro‐invertebrates in both riffles and margins in April 1985–87. Stream macro‐flora, substrata and marginal habitats were surveyed in May 1988.

2. TWINSPAN classification of the macroinvertebrate data indicated three major stream groups. One was distinguished by circumneutral pH and had a flora and fauna typical of such conditions. The other two groups consisted of acidic streams with moorland and conifer afforested catchments respectively. The forest streams were the more acidic but the two groups also differed significantly in the composition of their marginal habitats.

3 The acidic moorland streams had more vegetation (‘soft’ features) in the margins and supported several invertebrate taxa which were relative more abundant there than in the riffles. These taxa may be excluded from forest streams because the margins are ‘hard’ due to greater erosiveness and shading.

4. In view of the increasing cover by conifer afforestation in Britain, it is clearly necessary to elucidate all its effects on stream ecosystems, which include changes to the physical environment.
Genetic evidence of variation in the contributions of sexual and asexual reproduction to populations of the freshwater ostracod Candonocypris novaezelandiae
Authors: CHAPLIN JENNIE A. , AYRE DAVID J.
Published: May 2006

SUMMARY. 1 Genetic (electrophoretic) and sex ratio data were used to assess the contributions of sexual and asexual reproduction to recruitment to populations of the freshwater ostracod Candonocypris novaezelandiae in temporary and permanent water bodies of varying size.

2. Two distinct types of population structure were found. Populations from eight permanent ponds, a reservoir and a temporary pond, apparently comprised only females and were dominated by a few highly replicated genotypes. Significant departures from Hardy‐Weinberg equilibria were observed for at least one locus in all populations, and multi‐locus genotypic diversity ranged between 16% and 48% of that expected in a population with the same underlying gene frequencies reproducing solely by sexual means. These results were consistent with the predicted consequences of predominantly asexually derived recruitment.

3. In contrast, sexual reproduction was probably most important in a population inhabiting a large temporary swamp. This population displayed 79% of the genotypic diversity expected for a sexually reproducing population, and contained both males and females.

4. Most theoretical models predict that sexually reproducing individuals should have a selective advantage in unstable environments. The results of this study do not provide a perfect association of sexually derived recruitment with unstable habitats.
Hydrolytic extracellular enzyme activity in heterotrophic biofilms from two contrasting streams
Authors: JONES SUSAN E. , LOCK MAURICE A.
Published: May 2006

SUMMARY. 1. Extracellular hydrolytic enzyme activities and cell densities were monitored during undisrupted biofilm formation on pristine surfaces in two contrasting river sites in North Wales: an oligotrophic mountain stream (Nant Waen) and a mildly eutrophic river (River Clywedog).

2. Bacterial densities generally increased at both sites over a 33‐day monitoring period. Densities in the eutrophic site were approximately 14 times greater than in the mountain stream.

3. Using fluorescent substrate analogues, biofilms from Nant Waen produced low, variable xylosidase and β‐glucosidase activities. Biofilms from the more eutrophic River Clywedog produced higher xylosidase and β‐glucosidase activities and detectable endopeptidase, though these activities also fluctuated during the colonization period.

4. Unlike the other activities measured, esterase activities in the River Clywedog were correlated with cell densities (P<0.05). When extracellular esterase activities per cell were calculated, the oligotrophic biofilm was found to contain about twice as much extracellular esterase activity as the more eutrophic River Clywedog biofilm.
Effects of copper on species composition of benthic insects in a Sierra Nevada, California, stream
Authors: LELAND HARRY V. , FEND STEVEN V. , DUDLEY THOMAS L. , CARTER JAMES L.
Published: May 2006

SUMMARY. 1. Effects of copper on species composition and production of benthic insects in an oligotrophic stream dosed at low concentrations (2.5‐15 μg 1‐1 Cur; approximately 12‐75 ng 1‐1 Cu2+) were determined. Dosing was initially in autumn‐early winter when peak densities of many species occur. It was resumed the following summer near the time of egg hatch of most species and continued through the remaining aquatic stages of univoltine and multivoltine taxa.
Fish predation and reduction in body size in a Cladoceran population: palaeoecological evidence
Authors: SALO JUKKA , WALLS MARI , RAJASILTA MARJUT , SARVALA JOUKO , RÄSÄNEN MATTI , SALONEN VELI‐PEKKA
Published: May 2006

SUMMARY. 1 We studied the recent history (1852‐1982) of Lake Pyhä‐järvi, south‐west Finland, using both cladoceran microfossils and independent historical data. The objective of the study was to assess the impact of introduced planktivorous whitefish Coregonus lavaretus s.1. on zooplankton, especially on the main prey species Bosmina coregoni Baird s.str.

2. A size‐frequency analysis of carapace remains preserved in the sediments clearly shows a size shift in a Bosmina coregoni population. The carapace length of B. coregoni decreased by 11.0% after the introduction of the size‐selective planktivorous whitefish, indicating a parallel body‐size reduction.

3.During the study period no changes could be found in the carapace length of Chydorus sphaericus O. F. Müller, which was not preyed upon.
Classification and ordination of profundal macroinvertebrate communities in nutrient poor, oligo‐mesohumic lakes in relation to environmental data
Authors: JOHNSON RICHARD K. , WIEDERHOLM TORGNY
Published: May 2006

SUMMARY. 1. Profundal macroinvertebrates and water chemistry of sixty‐eight nutrient poor, poorly buffered lakes were sampled in 1983 or 1986. Assemblages of profundal zoobenthos were classified using two‐way indicator species analysis (TWINSPAN), ordinated by canonical correspondence analysis (CCA), and related to physico‐chemical factors using CCA. discriminant analysis, and regression.

2. 90% of zoobenthos (TWINSPAN) groups were classified correctly using discriminant analysis. Depth (Function 1), soluble reactive Si(OH)4 and HCO3, ‐(2), and phytoplankton biovolume and pH (3) were the strongest correlates with the three discriminant functions.

3. Regression analysis showed that depth, KmnO4, consumption, and phytoplankton biovolume were the best estimators of zoobenthos biomass in the profundal.

4. Multivariate analyses showed species assemblages amongst the profundal zoobenthos to be good indicators of lake type, particularly depth, pH, and phytoplankton biovolume.
Oxygen concentration profiles and exchange in sediment cores with circulated overlying water
Authors: SWEERTS JEAN‐PIERRE R. A. , LOUIS VINCE ST , CAPPENBERG THOMAS E.
Published: May 2006

SUMMARY. 1. The overlying water of intact sediment cores was constantly stirred with an impeller at a rate sufficient to mix turbulently the water column and maintain the diffusive boundary layer at a determined thickness. The system allowed standardization of water circulation in laboratory sediment core experiments.

2. Both oxygen concentration and oxygen penetration depth in the sediments decreased, the former by 70% and the latter from 4.2 mm to 2.0 mm, when the overlying water was not stirred for 24 h, as measured with oxygen microelectrodes in a lake sediment core.

3. Oxygen profiles measured in sediment cores in the laboratory were similar to those measured in situ when the overlying water was stirred with an impeller at such a rate that a similar thickness of the diffusive boundary layer at the sediment‐water interface developed in the laboratory as that in situ.

4. Sediment oxygen consumption was calculated from: (1) measured oxygen profiles in the diffusive boundary layer and the molecular diffusion coefficient for oxygen in water; (2) the measured oxygen decrease in the top of the sediments and the estimated diffusion coefficient in the sediment; and (3) by oxygen differences in the overlying water after incubation of sediment cores.
The influence of copper exposure on predator‐prey interactions in aquatic insect communities
Authors: CLEMENTS WILLIAM H. , CHERRY DONALD S. , JR CAIRNS JOHN
Published: May 2006

SUMMARY. 1. Vulnerability of two species of net‐spinning caddisflies (Chimarra sp. and Hydropsyche morosa) to predation by the stonefly, Paragnetina media, was significantly greater in experimental streams dosed with copper (target concentration=6 μg 1‐1) than in control streams.

2. Results of stomach analyses showed that Hydropsychidae was the major component of stonefly diets in experimental streams and that the number of Hydropsychidae per stonefly gut was significantly greater in dosed streams than controls.

3. Since these results could not be predicted using single species bioassays, we suggest that such simple tests be supplemented with more environmentally realistic procedures that account for species interactions.
Changes in phytoplankton over various time scales in a shallow, eutrophic: the Loch Leven experience with special reference to the influence of flushing rate
Authors: BAILEY‐WATTS A. E. , KIRIKA A. , MAY L. , JONES D. H.
Published: May 2006

SUMMARY. 1. The pattern of fluctuations in the total biomass and species composition of phytoplankton in the shallow, eutrophic Loch Leven exhibits considerable inter‐annual and within‐year variability. Nevertheless, studies over the 18‐year period reviewed here (1968–85) show that many of the observed changes can be explained in ‐terms of light regimes and the concentrations and fluxes of nutrients. On occasion, the incidence of fungal parasitism and of protozoan, rotiferan and crustacean grazing is also important.

2. Changes in annual mean algal biomass from very high levels in the late 1960s and early 1970s to somewhat lower levels in the late 1970s, followed by occasional high peaks in the present decade, are attributed to shifts in phosphorus loading‐particularly from a P‐rich industrial source.

3. In spite of complex and erratic sequences of algal species, seasonal patterns in the size distribution of the phytoplankton assemblage have been identified. However, these also changed. During the 4 years prior to 1971, Daphnia hyalina was not recorded in the plankton, and small algae have been abundant only in late winter or early spring.

4. The potential importance of the weather is highlighted as one of the possible causes of the irregular appearance of algal species. The effect of the characteristically variable, oceanicclimate of Northern Britain on this large (13.3 km2), shallow (z̄= 3.9 m) loch is thought to be of particular importance.

5. The influence of the weather on phytoplankton sequences is explored by comparing records of monthly flushing rate values with time‐series data on aspects of the aquatic environment and plankton populations. The preliminary assessment suggests that variation in flushing rate (p) has a considerable effect on temperature regimes and the supplies and in‐loch dynamics of nutrients; through such changes, p controls major features of phytoplankton succession such as the temporal abundance of diatoms, as well as detailed sequences of events relating to the development and collapse of particular algal species ‐ and. as a consequence, in some cases, of the animals preying on them.

6. Concluding remarks emphasize how little would have been understood about the functioning of shallow lakes, had the long‐term commitment to Loch Leven research been abandoned. The view is also expressed that the findings are of considerably greater relevance to research on ‘classic’ stratifying lake systems, than the focus on the shallow waterbody might hitherto have suggested.
Enzymic and chemical analysis of particulate organic matter from a boreal river
Authors: SINSABAUGH ROBERT L. , LINKINS ARTHUR E.
Published: May 2006

SUMMARY. 1. Benthic particulate organic matter (POM) was collected from a shallow pool of a fourth order boreal stream and sorted into seven size fractions ranging from 63 to >4000μm. Each size fraction was analysed for fibre, total phosphorus, and total Kjeldahl nitrogen. Microbial activity was measured by oxygen consumption and characterized by assaying for eleven classes of exoenzymes including cellulase, phenol oxidase, peroxidase, phosphatase and sulphatase.

2. Indices of detritus quality such as C/N, C/P, percent lignin, and microbial respiration showed improvement with decreasing particle size. Three covarying exoenzyme groups were identified: a carbohydrase‐phosphatase group that included eight enzymes, a phenol oxidase‐peroxidase group, and sulphatase. The activity of the carbohydrase‐phosphatase group, was significantly correlated with microbial respiration and the carbohydrate content of the POM. Phenol oxidase‐peroxidase activity was correlated with lignin content for POM greater than 250 μm, but activity increased markedly in the two smallest size fractions even though the lignin content of the POM continued to decline, Sulphatase activity was inversely related to particle size over the entire range.

3. The changes in microbial activity with particle size were attributed to the increasing surface area to volume ratio of smaller particles and to an ecological succession in the microbial community.
Phosphorus transformations in the epilimnion of humic lakes: biological uptake of phosphate
Authors: JONES R. I.
Published: May 2006

SUMMARY. 1. The hypothesis that dissolved humic material (DHM) stimulates bacterial involvement in phosphorus transformations and may thus lead to decreased accessibility of phosphorus to algae was investigated by studying three small forest lakes in southern Finland representing a wide range of concentrations of DHM.

2. Other chemical differences between the three lakes were slight, although the most humic lake exhibited higher concentrations of total phosphorus and of molybdate‐reactive phosphorus. Bacterial biomass did not differ significantly between the lakes, but algal biomass was significantly lower at higher DHM concentrations. Consequently the ratio of algal biomass to bacterial biomass was significantly lower in the most humic lake.

3. Uptake of phosphorus from added 33PO4 was partitioned between algal and bacterial size fractions by differential filtration. No significant variation between lakes was found in the proportion of particulate 33P recovered from the algal fraction.

4. Turnover times for phosphate were significantly longer in the most humic lake and also showed lower variability. In general turnover times were long in comparison with values reported from many other lakes. Only briefly in mid summmer did turnover times in two of the lakes shorten to values which would indicate that demand for phosphate was outstripping supply.

5. Short‐term storage of samples from the most humic lake stimulated biological incorporation of 33P, but additions of nitrogen and iron had little effect on phosphate uptake.

6. In these small forest lakes it is probable that no single nutrient consistently limits plankton development. Since no evidence was found that DHM shifts the balance of plankton phosphate uptake away from algae towards bacteria, the influence of DHM on phosphorus transformations may rather be through chemical regulation of free phosphate availability.
Phosphatase activity in relation to phytoplankton composition and pH in Swedish lakes
Authors: OLSSON HÅKAN
Published: May 2006

SUMMARY. 1. Potential phosphatase activity and phytoplankton from several lakes of different character were compared in order to evaluate the importance of lake water pH and phytoplankton composition for the activity and pH optimum of lake water phosphatases.

2. In oligotrophic lakes, in which phytoplankton biomass was most often dominated by Ochromonadaceae spp., optimum phosphate activity was found at pH values <6. In eutrophic lakes, where species of Cyanophyceae and Bacillariophyceae dominated the phytoplankton biomass, optimum phosphatase activity was found at pH 7.5 or 8.5.

3. The pH optimum of phosphatase activity often differed from the corresponding lake water pH.

4. Experimental variation in phosphorus availability resulted in predictable changes in phosphatase activity. However, specific phosphatase activity, calculated per biomass of phytoplankton, was dependent on plankton species composition.
Mayfly locomotory responses to endoparasitic infection and predator presence: the effects on predator encounter rate
Authors: BENTON MICHAEL J. , PRITCHARD GORDON
Published: May 2006

SUMMARY. 1. The effects of predaceous stoneflies and endoparasilism by mermithid nematodes on the locomotory behaviour of individual mayflies were studied in the laboratory. The effects of predator‐ and parasite‐induced changes in activity on predator encounter, attack and capture rates were also examined.

2. In response to predator presence non‐parasitized mayflies decreased activity, while parasitized mayflies increased activity, in comparison to a control group. As a result, the faster‐moving parasitized individuals encountered stonefly predators much more frequently. The frequency of attacks per encounter did not change.

3. In view of this and other studies, two predator‐avoidance strategies based on mayfly locomotory and defensive capabilities are proposed: (a) Mayflies that are able effectively to flee a predator's attack and those able to employ a behavioural defence may decrease their mean velocity when a predator is detected, thereby reducing the likelihood of an encounter while allowing foraging to continue; (b) Slower‐moving or otherwise defenceless mayflies may immediately move away from the area in which a predator is perceived in order to avoid an encounter.

4. In the absence of a predator, parasitized mayflies demonstrated greatly increased activity. This probably reflects increased foraging in response to the nutritional deficit imposed by the endoparasite. A decrease in upstream movement by parasitized mayflies may also indicate a parasite‐imposed energy stress.
The role of density in sex determination in Daphnia magna (Crustacea, Cladocera)
Authors: BARKER DAVID M. , HEBERT PAUL D. N.
Published: May 2006

SUMMARY. 1. Cladocerans are generally believed to exhibit environmental sex determination; however, the evidence for this assertion is equivocal. Particularly, no studies have been performed which isolate potential effects of the environment on the sex of offspring (and hence sex ratio) from effects on the induction of sex (with the necessary appearance of males). We report the findings of a study of Daphnia magna Straus which is able to make this distinction.

2. We examined the sexes of broods produced by asexually reproducing females collected from high and low densities of D. magna in naturally occurring populations. We looked for an effect of density, a factor frequently implicated in male induction, on offspring sex.

3. We could find no effect of density on brood sex. Our results may indicate a true absence of interaction or may arise from our sampling procedure obscuring an interaction. More detailed field observations are suggested as a means of further examining the role of density in sex determination in Cladocera.
OPINION Endless summer: internal loading processes dominate nutrient cycling in tropical lakes
Authors: KILHAM PETER , KILHAM SUSAN SOLTAU
Published: May 2006

SUMMARY. 1. Fossil diatom assemblages deposited in more than a dozen African lakes roughly 9500 years BP were dominated by a single planktonic species, Stephanodiscus astraea (Ehrcnb.) Grun. (although realistically this is likely to be a species complex). These diatoms flourished when lake‐levels were maximal. Data are included from many of (he large African lakes, and others extending from Lake Abhé0, Ethiopia, to Lake Cheshi, Zambia.

2. Because the ecological physiology of Stephanodiscus species is well known one can predict the nutrient regime that must have existed when Stephanodiscus bloomed. Owing to competition for resources Stephano‐discus species dominate when the supply ratio of silicon to phosphorus (in moles) in the epilimnion is relatively low (Si:P∼1). Consequently, lakes dominated by S. astraea are often hypereutrophic.

3. We propose a series of hypotheses to explain why tropical lakes have decreasing Si:P ratios as lake‐levels increase, primarily owing to internal P‐loading processes in the epilimnia. These observations appear to contradict present conceptions of the fundamental relationships governing nutrient loadings to and within lakes. Tropical lakes appear to have had increasing epilimnetic phosphorus loading as lake‐levels increased. In contrast, large, deep lakes in the temperate zone are usually oligotrophic, with high Si:P ratios.

4. Our major conclusion is that regeneration rates are greater than removal rates for phosphorus in tropical lakes as compared to temperate lakes, especially where epilimnelic mixing exceeds 50 m. Biological control of the elemental cycles dominate in tropical lakes, whereas nutrient cycles in temperate lakes are dominated by physical processes for a large part of the year. This results in major differences in the fundamental mechanisms of nutrient regeneration and their relationships to morphometric features of lakes in the two regions.
Comparative study of mathematical models for the relationship between water temperature and brood development time of Gammarus fossarum and G. roeseli (Crustacea: Amphipoda)
Authors: PÖCKL M. , TIMISCHL W.
Published: May 2006

SUMMARY. 1. The relationship between water temperature (T°C) and brood development time (d days for embryonic development time plus ‘post‐hatch time’) was investigated experimentally using animals from four populations of Gammarus fossarum (populations 1–4) and two populations of G. roeseli (populations 5 and 6) in Austrian streams.

2. Eleven mathematical models were examined as suitable functions to describe the relationship between d and T. The models were compared with respect to their goodness‐of‐fit and suitability for further quantitative, statistical analyses of intra‐ and interspecific differences between natural populations of G. fossarum and G. roeseli.

3. Statistical analyses were performed with logarithmically transformed values of d, in order to provide homogeneous variances between the different constant temperatures used. The following three‐parameter model was found to be the most suitable for the data:

image

This equation was fitted in its linear form:
image
Growth and reproduction in the freshwater crab, Potamon fluviatile (Decapoda, Brachyura)
Authors: MICHELI FIORENZA , GHERARDI FRANCESCA , VANNINI MARCO
Published: May 2006

SUMMARY. 1. The patterns of relative and absolute growth and the reproductive biology of the freshwater crab Potamon fluviatile were studied in a natural population inhabiting a hill stream close to Florence, Italy, over an annual cycle. Periodical inspections of a stretch of the stream were made and morphological and anatomical analysis carried out.

2. As in other decapods, the females are smaller than the males (they can however occasionally reach larger dimensions). This may be determined by a lengthening of the moulting interval in the females, by their higher energetic cost of reproduction (since reproduction occurs simultaneously with moulting, at least in this habitat) and/or by a higher mortality rate resulting from the risks associated with carrying eggs and vagility.

3. The analysis of relative growth in secondary sexual characters (abdomen width and major chela length) with respect to carapace length, shows that the pre‐puberty and puberty ecdysis occur at 15 and 35 mm carapace length respectively, which was also confirmed by the gonad weight, vas deferens in males, and the onset of vitellogencsis in females.

4. A delay between anatomical and functional (i.e. the ability to copulate successfully) maturity was observed in the males. Being larger may be an advantage in intra‐sexual competition for mating, but larger males, being more vagile, are also more likely to meet receptive females. The females may mate before their puberty moult and store sperms in their seminal receptacles for when they attain full maturity; this could be adaptive since opportunities of encountering males are few and far between in their adult phase, characterized by their vagile and amphibious habits.
Responses of zooplankton and zoobenthos to experimental acidification in a high‐elevation lake (Sierra Nevada, California, U.S.A.)
Authors: BARMUTA LEON A. , COOPER SCOTT D. , HAMILTON STEPHEN K. , KRATZ KIM W. , MELACK JOHN M.
Published: May 2006

SUMMARY. 1. During the summer of 1987 we conducted an acidification experiment using large enclosure at Emerald Lake, a dilute, high‐elevation lake in the Sierra Nevada, California, U.S.A. The experiment was designed to examine the effects of acidification on the zooplankton and zoobenthos assemblages of Sierran lakes.

2. Treatments consisted of a control (pH 6.3) and pH levels of 5.8, 5.4, 5.3, 5.0 and 4.7; each treatment was run in triplicate. The experiment lasted 35 days.

3. The zooplankton assemblage was sensitive to acidification. Daphnia rosea Sars emend. Richard and Diaptomns signicauda Lilljeborg decreased in abundance below pH 5.5–5.8, and virtually disappeared below pH 5.0. Bosmina longirostris (Müller) and Keratella taurocephala Ahlstrom became more abundant with decreasing pH. although B. longirostris was rare in the pH 4.7 treatment. These species might serve as reliable indicators of early acidification in lakes such as Emerald Lake.

4. The elimination of D. rosea in acidified treatments probably allowed the more acid‐tolerant taxa to increase in abundance because interspecific competition was reduced. Even slight acidification can therefore alter the structure of the zooplankton assemblage.

5. In contrast to the zooplankton, there was no evidence that the zoobenthos in the enclosures was affected by acidification.
Mineralization, pore water chemistry and phosphorus release from peaty sediments in the eutrophic Loosdrecht lakes, The Netherlands
Authors: SINKE ANJA J. C. , CORNELESE ADI A. , KEIZER PEER , VAN TONGEREN ONNO F. R. , CAPPENBERG THOMAS E.
Published: May 2006

SUMMARY. 1. Pore water chemistry in peaty sediment was monitored for a year at two representative locations of the eutrophic shallow Loosdrecht lakes. The Netherlands. Phosphorus fluxes over the sediment‐water interface were calculated using measured concentration gradients in the pore water and compared to fluxes measured under laboratory conditions. Results were analysed with Redundancy Analysis to detect patterns of variation in pore water chemistry and in measured and calculated fluxes, that could be ascribed to environmental variables.

2. It was demonstrated that phosphorus fluxes measured in long‐term laboratory incubations were not correlated to any of the pore water characteristics.

3. Initial phosphorus fluxes measured in sediment columns, which varied between −7.7 and 1330 μmol m−2: day−1, were correlated significantly to the calculated phosphorus flux over the sediment‐water interface.

4. The high correlation between calculated fluxes of ammonia, phosphorus and methane and measured initial flux of phosphorus, conclusively pointed to mineralization of organic matter as the driving force for phosphorus release from the sediment.

5. Redundancy Analysis demonstrated that the rates of mineralization and phosphorus release were only weakly related to temperature. They appeared to be especially stimulated by the autumnal decrease in temperature which was probably related to an extra input of organic matter.
Water temperature in a stream gravel bed and implications for salmonid incubation
Authors: CRISP D. T.
Published: May 2006

SUMMARY. 1. Water temperatures were recorded at hourly intervals in the gravel of a trout spawning area in a small stony stream at depths of 0–20 cm in 1985–86 and 0– 40 cm in 1987.

2. As depth within gravel increased, the size of the daily fluctuations reduced and their time of occurrence was delayed by about 12 min cm−1′ in 1985–86 and about 6 min cm−1 in 1987.

3. From October to February mean temperatures at 20 cm depth were, on average, 0.5°C higher than those at the gravel surface. This reflected elevated daily minima more than it reflected elevated daily maxima.

4. From March to July daily minima were lower and daily maxima were higher in the stream than in the gravel. Consequences were: (a) an appreciable increase in mean daily range at all depths in the gravel during the summer, (b) higher daily means (by an average of about 0.4°C) in the water than in the gravel in May to August.

5. Some implications for the early development of salmonid fish are considered.
OPINION Manipulating lake community structure: where do we go from here?
Authors: McQUEEN D. J.
Published: May 2006

SUMMARY. 1 More than 10 years experience with whole lake pelagic manipulation has suggested some general trends applicable to all freshwater pelagic communities and some specific trends related to lake depth.

2 Among the general trends is the observation that the trophic cascade is strongly damped. This means that changes in phytoplankton biomass can be assured only when the fish community is strongly manipulated.

3 Among the depth related trends is the observation that in shallow lakes, changes in fish community structure are more likely to have cascading impacts on phytoplankton than are changes in deep lakes.

4 In shallow lakes, fish removal frequently results in decreased turbidity which is associated with the development of dense macrophyte populations and significant reductions of algal standing stocks. The mechanisms involve: increased grazing by zooplankton, the removal of fish induced bioturbation and nutrient recycling, and direct and indirect macrophyte effects (shading, zooplankton refuges and competition for nutrients).

5 In shallow lakes, where planktivore biomass can be regulated and macrophyte development is acceptable, fish biomanipulalions are likely to result in reduced algal populations and improved water quality.

6 In deep lakes, where macrophytes are not as important, long‐term effects of fish manipulations are strongly dependent upon the probability of non‐grazable algal bloom development. This is determined by many factors (chemical, physical and grazer related) which modify the impact that grazers have on phytoplankton biomass.

7 In deep lakes, successful fish biomanipulations may only be effective when chemical and physical factors are altered to produce algal species compositions that permit strong top‐down control of prey by predators.
Suspension and settlement of particles in flowing water: comparison of the effects of varying water depth and velocity in circulating channels
Authors: REYNOLDS C. S. , WHITE M. L. , CLARKE R. T. , MARKER A. F
Published: May 2006

SUMMARY. 1. An experimental study is described, designed to test the hypothesis that the loss of particles from suspension in flowing water follows an exponential decay function, the exponent of which is influenced more by water depth than water velocity. Successive experiments employed suspensions of Lycopodium spores which were introduced into one of the FBA's circulating channels maintained at its Watcrston site, Dorset, under different combinations of water depth and pumping rate.

2. In each experiment, the concentration of introduced spores indeed declined exponentially through time. The bulked, transformed data‐set also conformed well to a single regression against a common time scale and which explained over 94% of the accumulated variances.

3. The variance unexplained by the regression was apportioned among components distinguishing between experiments, experimental differences in starting concentration, water depth and pumping rate (velocity). This analysis revealed that, after elimination of different initial concentrations, only water depth produced a significant effect, through its relation to the settling velocity of the Lycopodium. Thus, the hypothesis was not invalidated: water depth and not Row velocity proved to be the main controlling variable determining the rale of sinking loss in these experiments. Flow velocity is, nevertheless, an important component only in the sense that it influences the horizontal distance travelled by the residual spore suspension through the time period required for complete settlement.

4. The consequences of experimental findings are applied to the maintenance of planktonic diatoms in rivers: both the survival of a potential growth inoculum and its downstream dispersion are strongly time‐dependent and are enhanced by greater channel depths.
Dissolved organic carbon concentrations and fluxes along the Moisie River, Quebec
Authors: FORD T. E. , FORD S. A. , LOCK M. A. , NAIMAN R. J.
Published: May 2006

SUMMARY. 1. The main stream and tributaries of a 145 km reach of the Moisie River, Quebec, were examined for temperature, conductivity, pH, dissolved organic carbon (DOC),%DOC>100,000 nominal molecular weight (NMW), optical density (OD350), and the ratio of OD400 to OD600 (E4:E6).

2. Dissolved organic carbon concentrations correlated closely with OD350 (r2=0.92, P<0.001). However,%DOC>100,000 NMW did not correlate with the E4:E6 ratio.

3. Except for a slight increase in%DOC> 100,000 NMW (r2=0.37, P<0.05), no change in any characteristic occurred down the length of the Moisie River, despite consistently higher levels of DOC in the tributaries.

4. Results suggest that high concentrations of DOC in tributary waters are rapidly removed within the main river channel. These results are discussed in terms of both biotic and abiotic models of in‐strcam processing.
Home range of juvenile Atlantic salmon, Salmo salar, and brown trout, Salmo trutta, in a Norwegian stream
Authors: HESTHAGEN T.
Published: May 2006

SUMMARY. 1. The sizes of home ranges of juvenile Atlantic salmon (age 1 +) and brown trout (age 2+ to 9+) in a Norwegian coastal stream were estimated by local movements of batch‐marked fish from 12.5 and 25 m long sections. Only recoveries made in the release section and in up‐and downstream neighbouring sections were considered.

2. There was no significant difference in the average percentage of recaptures of salmon and trout between 12.5 and 25 m sections; a stream area of about 40–50 m2 defines the size of home range for stocks of both species.

3. The fraction of brown trout recaptured in release sections increased with increasing fish densities, indicating a smaller home range under these conditions.