bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zooplankton feeding rates in relation to suspended sediment content: potential influences on community structure in a turbid reservoir
Authors: HART R. C. 
Published: May 2006

SUMMARY. 1. Changes in zoopiankton composition and abundance in Lake le Roux, a turbid subtropical reservoir on the Orange River in South Africa, were correlated with changes in water transparency (related to suspended sediment levels) during a 7 year field study. Results of radiotracer studies of the effect of mineral turbidity on zooplankton feeding rates which potentially influence competitive ability, and thus community structure, are reported here.2. Feeding rates of five zooplankters were very variable, but consistently declined with rising turbidity: rates of decline differed between species. A regression estimate of the critical turbidity threshold at which food intake matched the estimated respiratory need was derived for each species. This yielded the following “turbidity‐tolerance” ranking: Moina brachiata Jurine > Metadiaptomus meridianus (van Douwe) ×Daphnia gibba Methuen > D. barbata Weltner > D. longispina O. F. Muller. The consistency between this ranking and one based upon abundance‐transparency relationships in the field study suggests that community structure is related to differential feeding capabilities, although other influences are not excluded.3. Tests on D. gibba and M. meridianus failed to reveal any detectable feeding rate saturation (incipient limiting food level) below 1.2mg 1−1 C. The relative reduction in feeding rates at elevated turbidity was nearly 3 times greater for the daphnid than the copepod over a range of food concentrations, and considerably reduces the competitive ability of this (and other) daphnids. The turbidity tolerance disparity between Moina and the daphnids demonstrates a more complex situation than a simple copepod/cladoceran dichotomy. These findings and their implieations are discussed in relation to wider features of zooplankton ecology.
Relative vulnerability of six freshwater gastropods to the leech Nephelopsis obscura (Verrill)
Authors: BROWN KENNETH M. , STROUSE BRIAN H. 
Published: May 2006

SUMMARY. 1. The vulnerability of six species of freshwater snails to the leech Nephelopsis obscura was determined in laboratory predation experiments.2. Nephelopsis was unable to prey on prosobranch snails with an operculum, but did consume certain pulmonate species though predation rates were low, ranging from one to two snails per leech per night at 20°C. Apparently, Nephelopsis does not actively select prey, but merely consumes those species most easily handled.3. Among pulmonates, leeches captured species in the following order: Physa gyrina (Say), Helisoma anceps (Menke). Lymnaea emarginata (Say) and Helisoma trivolvis (Say). Susceptibihty of size classes varied among snail species.4. Neither environmental structure, such as cobble or macrophytes, nor gastropod escape behaviors, such as clamping to substrates or vertical migration away from bottom‐feeding leeches, lowered capture rates by Nephelopsis.5. In 2 years sampling, only one of seven lakes, however, had appreciable abundances of Nephelopsis. It is therefore suggested that the rarity, low feeding rates, and lack of strong gastropod preference limit the effect of Nephelopsis on field gastropod distributions.
The chemical ecology of some British freshwater gastropod molluses: behavioural responses to short chain carboxylic acids and maltose
Authors: DALDORPH P. W. G. , THOMAS J. D. 
Published: May 2006

SUMMARY.1. The behavioural responses of six species of British freshwater gastropods to chemical gradients of short chain carboxylic acids (C‐2 to C‐5, C‐8) and maltose were investigated by means of diffusion olfactometers.2. The species were ranked as follows on the basis of the number of significant behavioural responses to the test chemicals:Lymnaea peregra>Planorbis contortus > Physa fontinalis > Planorbis planorbis > Bithynia tentaculata > Planorbis vortex.These differences were not a result of differences in activity but reflect real differences in ehemoreception.3. Propanoate (C‐3) was a significant attractant or arrestant to five snail species, C‐4, C‐8 and maltose to four species and C‐5 to three species. Acetate (C‐2) was a significant attractant toL. peregraandP. fontinalisbut it was the only acid to act as a repellent, toP. planorbisandB. tentaculata.4.Lymnaea peregracontinued to respond to repeated butanoate application. Response levels could be enhanced by increasing concentration (minimum thresholds 10‐4M to 10−5M), pH (above 6) and food deprivation.5. The ecological relevance of the results are discussed with particular reference to the distributional patterns of the chemicals and snails and the feeding niches of the latter.
Effects of low pH and humus on the survivorship, growth and feeding of Gammarus pulex (L.) (Amphipoda)
Authors: HARGEBY A. , PETERSEN R. C. 
Published: May 2006

SUMMARY. 1. The toxicity to the freshwater amphipod Gammarus pulex (L.) of soft water (pH6.0) with three concentrations of XAD‐extracted aquatic humus was treated in the laboratory.2. Exposure to pH6.0 water without humus added resulted in 92% mortality after 3 weeks. Humus, added at concentrations of 7 and 20 g Cm 3, decreased the mortality to 80% and 64% in the same period.3. Surviving animals kept at pH6.0 had a lower growth rate, lower food conversion efficiency and higher body water content than animals kept at pH 7.3.4. Humus had no significant effects on growth, food conversion or body composition of G. pulex kept at pH 6.0. However, there was a tendency for growth and food conversion to increase, and for body water content to decrease with increased humus concentration. The effects of humus on growth and food conversion of G. pulex observed in this study do not support the contention that humus acts as a free coupler to lower metabolic efficiency. On the contrary, humus tended to benefit food conversion.5. It is suggested that low concentrations of humus can be directly beneficial to organisms in acidified water in ways other than by complexing toxic metals.
The relative importance of algae and bacteria as food for Daphnia longispina (Cladocera) in a polyhumic lake
Authors: KANKAALA PAULA 
Published: May 2006

SUMMARY. 1. Grazing on algae and bacteria by the planktonic cladoceran, Daphnia longispina, was studied in a small polyhumic lake with low phytoplankton primary production in southern Finland.2. D. longispina filtered algae at average rates of 0.09‐0.82 ml ind−1 h−1. The filtering rates on bacteria were 26‐92% of those on algae in parallel experiments.3. From June to August algae, including mixotrophic and heterotrophic forms, comprised 56‐93% of the food ingested by D. longispina. In mid‐September and early October, when the Daphnia population was declining and the algal biomass was low, bacteria comprised 73% and 55% respectively of the food of Daphnia.4. For D. longispina, an energy pathway via bacteria and bactivorous flagellates is probably a more important link to allochthonous organic matter than direct utilization of epilimnetic bacteria.
Dissolved organic matter in Cumbrian lakes and streams
Authors: TIPPING E. , HILTON J. , JAMES B. 
Published: May 2006

SUMMARY. 1. A survey of dissolved organic carbon concentration [DOC] and optical absorbance at 340 nm (A340) was carried out for thirteen lakes and twenty‐three streams in Cumbria over the period May 1986 to April 1987.2. Values of [DOC] were in the range 0‐6.2 mg 1‐1‐1, no water having a mean [DOC] greater than 3.6mgI‐1. Streamwaters showed no gross seasonal dependence in [DOC], but there was a peak in [DOC] associated with the first major rain event of autumn 1986. Summer values of [DOC] in lakes were greater than winter values, probably because of the production of DOC by phytoplankton.3. In streams, [DOC] was weakly positively correlated (r2 <0.3) with discharge (as estimated from rainfall); A340 was more strongly correlated (0.4 < r2 < 0.6). Linear regression of mean A340 against mean [DOC] for streams gave a slope consistent with the absorptivities of aquatic humic substances, and a positive intercept on the abscissa that suggests the presence of, on average 0.6 mg 1‐1 of DOC that does not absorb at 340 nm. Lake samples taken in winter gave a similar A.340/[DOC] relationship to that for streams, but in summer A340/[DOC] ratios were lower, suggesting that phytoplankton‐derived [DOC] absorbs weakly or not at all at 340nm.
Competition for space by predators in streams: field experiments on a net‐spinning caddisfly
Authors: LANCASTER JILL , HILDREW ALAN G. , TOWNSEND COLIN R. 
Published: May 2006

SUMMARY. 1. Field experiments in a fishless stream were carried out on an abundant caddisfly with a predatory, net‐spinning larva, Plectrocnemia conspersa (Curtis), to assess whether net site availability affects their microdistribution.2. Net sites were supplemented by adding nought, one or four artificial structures to replicated patches on the stream bed. In each of three experiments at different seasons (summer, autumn and late winter), caddis densities increased significantly in patches with extra net sites.3. The response of caddis to supplemented net sites could be affected by the subsidiary effects of food and offish. These potential interactions were assessed in each experiment by varying net site density in two additional treatment stretches in which (1) prey abundance was increased by releasing Daphnia, and (2) brown trout (Salmo trutta L.) were enclosed. The responses of caddis in these two treatments were compared to that in the reference stretch, where only net site density varied.4. Increased food abundance enhanced the response of caddis to net site supplementation in winter, when natural prey was least abundant, but not in summer or autumn. We suggest that extra food affects the mechanism determining net building only when prey availability is below some threshold.5. The presence of fish precluded any effect of extra net sites in summer, but had no effect in autumn (the winter fish treatment was lost). We suggest fish predation reduced the densities of caddis in summer, so that net sites no longer limited local densities. In autumn, fallen leaves provided refugia from fish, which consequently were less effective predators of P. conspersa.
Beluga whale ecology: a concern of freshwater biologists?
Authors: WATTS P. D. , DRAPER B. A. 
Published: May 2006

SUMMARY.1. Churchill estuary beluga whales displayed their highest densities in freshwater habitat, suggesting preferential use.2. Whale densities in freshwater were as high as 350 animals km−2and represented over one tenth of the estimated Hudson Bay population.3. Future environmental assessments of hydroelectric development in northern Manitoba, Canada, must consider the effects on the beluga whales.
Very high secondary production at a lake outlet
Authors: WOTTON R. S. 
Published: May 2006

SUMMARY. 1. Larvae and pupae of Simulium noelleri Fried, coated the concrete of parts of an artificial lake outlet in southern England.2. In the first two (of three) summer generations, development was synchronous and this allowed the calculation of their secondary production by the instantaneous growth method. The production of the two summer generations was, respectively, 229.1 g C m−2 (7.4 g C m−2day−1) and 185.5 g C m−2 (8.8 g C m−2 day−1) The contribution of the third summer generation, and the overwintering generation, to annual production would be less than that of the first two summer generations. Nevertheless, annual production will have exceeded 500 g C m−2 at this site.3. Larvae are suspension feeders and they captured the rich supply of particulate and dissolved organic material which passed over them after export from the lake. As food is brought to the larvae they only require space for attachment and can thus build up very high population densities (which exceeded 1 × 106 m−2 on some occasions during the summer). The high population densities result in a high biomass and hence in the high levels of production.
The abundance of phytophilous invertebrates on different species of submerged macrophytes*
Authors: CYR HÉLÈNE , DOWNING JOHN A. 
Published: May 2006

SUMMARY. 1. We tested Krecker's model (1939) which states that the abundance of invertebrates per unit macrophyte biomass varies with plant species and is higher on plants with finely dissected leaves than on plants with broad leaves. The abundance of invertebrates was measured in thirteen lacustrine macrophyte beds in southern Québec, Canada. The model was tested for the total abundance of invertebrates and for the abundances of Chironomidae, Cladocera, Cyclopoida, Gastropoda, Hydracarina, Ostracoda and Trichoptera.2. More epiphytic invertebrates were found on the dissected Myriophyllum spp. than on the broad‐leaved Potamogeton amplifolius Tuckerm, P. robbinsii Oakes and Vallisneria americana Michx. (P<0.01). More invertebrates were also found on P. amplifolius than on P. robbinsii or V. americana (P<0.01). The total abundance of invertebrates was not systematically related to the degree of plant dissection.3. The abundances of Chironomidae, Cladocera, Cyclopoida, Gastropoda, Hydracarina, Ostracoda and Trichoptera varied on different plant species (P<0.01). Contrary to Krecker's hypothesis, however, macrophytes with finely dissected leaves (Ceratophyllum demersum and Myriophyllum spp.) did not in general support more invertebrates per unit plant biomass than plants with large leaves (Potamogeton amplifolius, P. robbinsii and Vallisneria americana).
Limnological imbalances: an antipodean viewpoint
Authors: WILLIAMS W. D. 
Published: May 2006

SUMMARY. 1. It is argued that modern limnology is excessively concerned with the study of fresh waters in the northern temperate region. Limnology has been and is unbalanced in its interests and emphases and, as a result, many widely held limnological concepts need revision.2. The genesis of the argument is outlined. It involved the initial assumption that Australia was limnologically distinctive. Later, it was realized that since most of the world is arid, semi‐arid, tropical or semi‐tropical, Australia was much less distinctive than originally thought.3. Other limnological assumptions considered in the paper concern saline lakes and salinization, the importance and nature of temporary bodies of standing fresh water, biological diversity in tropical fresh waters, the evolutionary importance of permanent freshwater lakes, and the global applicability of the River Continuum Concept. Consideration suggests that some widely‐held views on these matters are erroneous.4. Thus, saline lakes are more important (scientifically, commercially), widespread and numerous environments than is generally thought. Salinization is a significant environmental hazard for many rivers in semiarid regions. Temporary bodies of standing fresh water are geographically widespread and abundant aquatic environments with high species diversity, and in which many species have restricted distributions and low dispersal abilities. Biological diversity appears to be low in tropical fresh waters. Permanent freshwater lakes are perhaps less important loci for the evolution of the freshwater biota than generally thought, temporary fresh waters more so. Finally, the River Continuum does not seem to be applicable to many running waters outside the north temperate region.5. A number of suggestions are made of how a better balance in limnology may be arrived at: how a more globally comprehensive intellectual framework may be built. Suggestions include: an increased awareness of the frequently different natures of waters within and beyond the northern temperate region; recognition of the potential benefits to be gained from the study of waters outside the northern temperate region;
Prey selection by the dobsonfly larva, Protohermes grandis (Megaloptera: Corydalidae)
Authors: HAYASHI FUMIO 
Published: May 2006

SUMMARY 1. Prey selection by the dobsonfly larva, Protohermes grandis (Thunberg), was studied in stony riffles of the Yataro River, central Japan. The density, size distribution and taxonomic composition of available prey were assessed for 2 years. In order to know the encounter rate between prey and this ambush predator, prey mobility was also estimated from patterns of colonization of experimentally detiuded stones.2. Foregut analyses revealed that maximum size of prey eaten increased with larval size, and large larvae did not take the smallest prey in spite of high availability in all seasons.3. Charnov's (1976) optimal diet model quantitatively predicted such size‐selective feeding under seasonally fluctuating conditions of water temperature and prey availability. Larvae maximized the feeding rate by selecting prey.4. Maximum width of prey eaten coincided approximately with larval mandible length. Mandible size seemed to play an important role in the selection of prey in the optimal size range.
Life histories of some species of Chydoridae (Cladocera: Crustacea)
Authors: ROBERTSON ANNE L. 
Published: May 2006

SUMMARY 1. Life history parameters of two species of Chydoridae (Leydigia leydigi and Disparalona rostrata) were studied in the field and in the laboratory.2. For both species the number of juvenile instars was variable and tentatively related to initial size of neonate. Egg volume increased with increasing parent length and with decreasing temperature; possible advantages gained by the offspring are discussed in relation to invertebrate predation.3. The life history strategy employed by the littoral Chydoridae is compared to that of large and small planktonic cladocerans. Small planktonic cladocerans and the Chydoridae (except the Eurycercinae and the Saycinae) produce large young relative to their size at maturity and mature early. However, unlike the small planktonic cladocerans, growth in the Chydoridae is curtailed after the onset of reproduction and in this they resemble the large planktonic cladocerans. This strategy may be related to vertebrate predation and the presence of vegetation in the habitat.
The loss of submerged plants with eutrophication II. Relationships between fish and zooplankton in a set of experimental ponds, and conclusions
Authors: IRVINE KENNETH , MOSS BRIAN , BALLS HILARY 
Published: May 2006

SUMMARY. 1. In 1982 and 1983 sets of experimental ponds were left with their submerged plant communities intact (plant ponds) or were cleared manually of them (cleared ponds). The ponds were all fertilized with ammonium nitrate and with variable amounts of phosphate. In 1982 fish were removed from the ponds. Zooplankton communities were dominated by large Cladocera with Daphnia prominent in the cleared ponds and Simocephalus in the plant ponds. There was no detectable effect of differential phosphorus additions on zooplankton communities or populations.2. In 1983 zooplanktivorous fish (mainly roach) were stocked in the ponds. In the plant ponds the fish did not survive, probably through severe deoxygenation and the zooplankton community again included large‐bodied Simocephalus. Fish survival was variable in the cleared ponds. Where fish stocks were absent or low (0.5–1 g m−2) a Daphnia‐ dominated community persisted; at intermediate fish stocks (18.1 g m−2) Eudiaptomus gracilis was predominant and where fish stock was high (22.8–29.1 g m−2) Bosmina longirostris, and cyclopoid copepods dominated the communities. Mean biomass of the zooplankton community declined with increase in fish stock to between 5.1 and 18.1 g m−2 then increased.3. On the basis of results from the experimental ponds and elsewhere, a new hypothesis is put forward to account for the switch from aquatic plant to phytoplankton dominance in eutrophicated shallow lakes. It envisages dominance by either group to be possible as alternative states over a wide range of high nutrient loadings. It suggests that each state is buffered against increased loading by mechanisms involving plant and algal physiology and zooplankton grazer populations. The nature of the buffers and the reasons by which one state may be switched to the other are, discussed.
The loss of submerged plants with eutrophication III. Potential role of organochlorine pesticides: a palaeoecological study
Authors: STANSFIELD JULIA , MOSS BRIAN , IRVINE KENNETH 
Published: May 2006

SUMMARY. 1 Mechanisms which might have caused a switch from submerged plant dominance to phytoplankton dominance in a series of shallow lakes, the Norfolk Broads, during the 1950s and 1960s, are reviewed. It is argued that a likely mechanism was a poisoning of the community of Cladocera which graze on algae and are associated with the plants. This allowed phytoplankton to take advantage of the increased nutrient loadings and to increase. The 1950s and 1960s were periods of liberal organochlorine pesticide use. Cladocera are particularly susceptible to organochlorine toxicity.2. Sediment cores were taken from Hoveton Great Broad, in which the switch to phytoplankton has occurred, and from two Broads (Upton and Martham South Broads) in which submerged plants are still dominant. Analyses were made for cladoceran remains, diatoms and molluscs. Cross dating with previously taken dated cores allowed time‐scales to be applied.3. In Hoveton Great Broad, a switch from clear‐water‐associated chydorids to turbid‐water forms was found to coincide with the loss of aquatic plants in the 1950s. No Daphnia remains were found. In the other two Broads, clear‐water chydorids, mostly plant‐associated, were found throughout the cores.4. Residues of dieldrin (HEOD), DDD and TDE were found in the Hoveton Great Broad cores, with the DDT derivatives particularly associated with the end of the phase of submerged plant dominance and the beginning of that of phytoplankton dominance. Bosmina remains became more abundant after this point. Pesticide residues were scarce in the cores from the other two Broads and did not form any particular pattern. Residues of polychlorinated biphenyls were widespread in all cores.5. Calculation of DDT concentration in the water at the time the sediments with greatest concentrations of residue were laid down suggests that concentrations above typical LC50 values for Daphnia species could have been present.
Energy maximization and foraging strategies in Potamon fluviatile (Decapoda, Brachyura)
Authors: GHERARDI FRANCESCA , TARDUCCl FEDERICA , MICHELI FIORENZA 
Published: May 2006

SUMMARY. 1 Foraging of the freshwater crab Potamon fluviatile was studied by recording the activity of seventy‐eight specimens in a 50 m2 pool in a Tuscan stream during early summer. Foraging was related both to the organic content of the substrate and to the crabs’ oxygen consumption. During this period, adult females underwent “second vitellogenesis”. with abundant deposition of yolk in oocytes.2. A dispotic distribution (not accompanied by agonistic interactions, but ‘peacefully’ based on size) was observed within the foraging area. Larger animals (mostly males) fed on the rare patches of vegetable debris, which presented the highest organic content. Conversely, smaller specimens were relegated lo the poorer substrates, such as the stream banks.3. The females extended and diversified their foraging areas by also venturing into terrestrial habitats, in contrast to the more sedentary and aquatic males. This behaviour (which was not accompanied by a different energetic output) resulted in a more proteinaceous diet (even when the N‐content of vegetable debris fell drastically), and in a significant increase in fats and the hepatopancreas index.4. The reserves of energetic substances are presumed to sustain the highly expensive vitellogenesis, with the production of macrolecithal eggs. The females’ behaviour as energy maximizers’ seemed to be under a strong selective pressure, since their reproductive success is directly related to the efficient harvesting of food.