bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epiphytic diatoms in two freshwater maritime Antarctic lakes
Authors: OPPENHEIM DEBORAH R. , GREENWOOD RICHARD 
Published: May 2006

SUMMARY.

An ecological study of two small maritime Antarctic lakes on Signy Island, South Orkney Islands, was undertaken from January 1986 to March 1987. Analysis of diatom counts from the lakes provided examples of oligotrophic and mesotrophic ecosystems.
A diverse community of 104 epiphytic taxa was identified. Twenty‐eight taxa had a percentage abundance greater than 1% in both lakes. Distinctive dominant taxa were identified from each lake.
A variety of ordination techniques was performed on the abundance data and a principal components analysis demonstrated differences in the diatom assemblages between the two lakes. Clear separations of sites and species were evident between the lakes, and accounted for the greatest percentage variance.
Species composition varied with depth within each lake and was also important in influencing changes in assemblage composition between sites.
A redundancy analysis indicated that species composition was correlated to concentrations of nitrogen and phosphorus but the total variance accounted for by the four physical and chemical factors measured was low (24%).
The population dynamics of Chydoridae and Macrothricidae (Cladocera: Crustacea) from the River Thames, U.K.
Authors: ROBERTSON ANNE L. 
Published: May 2006

SUMMARY.

A study was made of the population dynamics of benthic cladocerans in the River Thames, U.K. These included three species of Chydoridae (Alona affinis Leydig, Disparalona rostrata (Koch 1841) and Leydigia leydigi Schodler) and one species of Macrothricidae Iliocryptus sordidus (Lievan).
The pattern of chydorid abundance was similar to that found in many lakes: a midsummer peak followed by a sharp decrease in numbers and subsequent low abundance. This was caused by a temporary decrease in natality, possibly due to food limitation, and a more permanent increase in mortality, thought to be due to predation.
Iliocryptus sordidus differed considerably from the chydorids, the major population peak occurring in the autumn. The lifestyle and adult size of Iliocryptus sordidus (Lievan) must render adults less vulnerable to invertebrate and fish fry predation.
A literature survey showed that the assemblage of species found in the unvegetated littoral of lakes and rivers included a taxocene of cladocerans.
Distribution and production of Chironomidae (Diptera) in the lower course of the Grabia River (Central Poland)
Authors: GRZYBKOWSKA M. , WITCZAK J. 
Published: May 2006

SUMMARY.

A fifth‐order section of the Grabia River was investigated over two years: 1984/85 (low water level) and 1985/86 (high spate). Chironomidae (thirty‐nine species) dominated the macrobenthos in both years.
In 1984/85 (mean annual water temperature 10.2°C), the number of Chironomidae species in coarse sediment was highest in spring (thirty‐three species) while in sand it was highest in summer (fifteen species). A decrease in species richness was recorded in autumn and winter at each of the established sites. The estimated Chironomidae production for the whole river section was 5.37 g dry wt m−2 yr−1, but it differed widely amongst the study sites, ranging from 3.75 to 12.07 g m−2 yr−l.
In 1984/85 (mean annual temperature 8.1°C) there occurred a summer spate which was more intense than any recorded over the previous 20 years. This substantially reduced the number of species, the greatest reduction being in the coarse sediment, which was buried with sand during the spate. Production for the whole section decreased to 1.17 g m−2 yr−1, and the variability amongst sites ranged from 1.04 to 1.45 g m−2 yr−1.
Effect of selective planktivory by fry of Rhamdia sapo (Pimelodidae: Pisces) on zooplankton community structure
Authors: ZAGARESE HORACIO ERNESTO 
Published: May 2006

SUMMARY.

The direct and indirect effects of predation by larval fish (Rhamdia sapo) on zooplankton in rearing tanks are analysed. Rhamdia sapo larvae showed an unusual species‐selectivity for Acanthocyclops robustus, the main invertebrate predator present.
Acanthocyclops robustus populations were markedly reduced, presumably as a direct consequence of species‐selective removal. Other zooplanktonic prey were not significantly affected by R. sapo predation.
Rotifers increased in tanks with fish, but this was not related to herbivorous crustacean variables (biomass, mean weight, abundance and species composition). On the contrary, rotifer biomass was negatively correlated with some A. robustus variables (biomass and mean weight of adults + copepodites and nauplii biomass). Thus, the rotifer increase appears to be an indirect effect of predation on A. robustus by R. sapo larvae.
Effect of food concentration on growth, reproduction and survivorship ofBosmina longirostris(Cladocera)
Authors: URABE JOTARO 
Published: May 2006

SUMMARY.1. Body growth, reproduction and survivorship ofBosmina longirostriswere monitored at four food concentrations (0.05, 0.10, 0,25 and 2.50 ing Cl−1) to examine the extent to which food concentration affects these life‐history parameters.2. Food concentration had a significant effect on growth, and most of the reproductive parameters (size and age at maturation, brood size, instar duration and egg development time). More than 60% of animals died before maturation at the lowest food concentration, although most animals survived until maturation at other food concentrations.3. Change in life‐history parameters resulted in a decrease in rate of population growth (r) from 0.310 to 0.020 day−1with decreasing food concentration, showing that this cladoceran is highly food‐limited in many lakes.4. Importance of the effect of food concentration on egg development time was emphasized in relation to analysis of natural populations.
Cladoceran assemblages, seasonal succession and the importance of a hypolimnetic refuge
Authors: TESSIER ALAN J. , WELSER JENNIFER 
Published: May 2006

SUMMARY.
1. We investigate the importance of a refuge from fish predation to the abundance, species composition and seasonal succession of zooplankton. Thirty lakes representing a range of depths were sampled twice in summer for physical/chemical parameters and zooplankton community structure.2. We define the refuge from centrarchid predators to be that space between the thermocline and the zone of anoxia. As lakes vary in rate of oxygen depletion from the hypolimnion. the refuge size and lake depth are independent: refuge size decreases during the summer period.3. Lake depth and refuge size independently explain variation among lakes in zooplankton species composition, but seasonal community change within lakes is best predicted by loss of refuge size.4. Refuge size also explains the substantial variation in the relative dominance of the two major daphnid species. Lakes possessing a large refuge are dominated by D. pulicaria; those with a small refuge are dominated by the smaller, D. galeata mendotae. We suggest that lakes of intermediate refuge size, which are characterized by high species diversity, represent a more equitable balance of predation and competition.
Taxonomic structure of phytoplankton assemblages in Crater Lake, Oregon, U.S.A.
Authors: DEBACON M. K. , MCINTIRE C. D. 
Published: May 2006

SUMMARY.
1. A taxonomic analysis of 171 phytoplankton samples obtained from Crater Luke, Oregon, between 1985 and 1987 revealed 132 taxa in the upper 250 m of the water column. The greatest temporal variation in taxonomic structure occurred between 40 and 80 m below the water surface, a depth range which corresponded to the zone of maximum primary production.2. Phytoplankton cell biovolume in the upper 20 m of the water column was relatively high during the summer months, a period when Nitzschia gracilis was dominant in the epilimnion. However, 72% or more of the cell biovolume between 0 and 200 m was distributed below 20 m and, during the winter and spring months, 61% was found below 80 m.3. Cluster analysis identified a sparse, temporally ubiquitous flora which was modified to various degrees when environmental conditions became favourable for the growth of a few dominant taxa. These surges ot dominance by individual taxa accounted for 2 to 5‐fold increases in cell biovolume and generated a pronounced taxonomic discontinuity between the floras in the epilimnion and hypolimnion.4. While the taxonomic structure of the phytoplankton in the epilimnion corresponded closely with the structure found in a 1978–80 study, the flora below the metalimnion was more diverse and less predictable in species composition than the pattern reported in the earlier study.
Exploitation of prey by a river bird, the dipper Cinclus cinclus (L.), along acidic and circumneutral streams in upland Wales
Authors: ORMEROD S. J. , TYLER STEPHANIE J. 
Published: May 2006

SUMMARY.
1. The diet of the Eurasian dipper Cinclus cinclus. a riverine bird from a globally widespread genus, was assessed through all stages of its annual cycle using published data and field studies from streams of contrasting chemistry. Time‐activity budgets were also compiled throughout the year and used to estimate annual energy requirements from the stream ecosystem.2. The annual energy requirements for a territorial pair ranged from 148,000 to 158,000 kJ yr−1 depending on whether one or two broods were reared. After allowing for assimilation efficiency, these requirements were estimated to represent 10.5–11.0 kg dry mass of fish and invertebrates. Using representative values for territory size (4680–11,250 m2), annual exploitation of secondary production was estimated at 0.93–2.35 g dry mass m−2.3. Several features combined to focus the predatory load on certain organisms over different stages of the annual cycle. These included the availability and selection of alternative prey, the need to provision nestlings with large items such as trichopteran larvae, and the use by females of calcium‐rich prey such as fish prior to egg formation.4. Across their range of territory size, annual exploitation (dry mass) by dippers was estimated at 0.06–0.29 g m−2 for Plecoptera. 0.02–0.22 g m−2 for Ephemeroptera. 0.59–1.11 g m−2 for Trichoptera and 0–0.78 g m−2 for fish. Exploitation of Ephemeroptera. I richoptera and fish were all highest in circumneutral streams, but exploitation of Plecoptera was highest in acidic streams because other prey were scarce.5. Cottids dominated the fish component of the diet. Influences on their density could be substantial according to available data on production in Welsh streams. Hydropsychids and limnephilids dominated the trichopteran component, with exploitation again representing potentially substantial amounts of production. Contemporaneous data are required on benthic production and exploitation by the birds.6. The ecological role of birds in rivers particularly, and aquatic ecosystems generally, is currently neglected but worthy of considerable research effort.
Ecology of leptocerid caddisfly larvae in an intermittent South Australian stream receiving Eucalyptus litter
Authors: TOWNS D. R. 
Published: May 2006

SUMMARY.
1. Brown Hill Creck, a small intermittent stream in dry sclernphyll forest in South Australia, flows for about 6 months during winter and spring. When flow ceases the stream dries to isolated pools which receive high summer inputs of Eucalyptus obliqua litter. Decomposition of this material in remnant pools causes extremely dark waters and depressed oxygen concentrations for up to 90 days.2. Only two fully aquatic insect species, Lepntorussa darlingtoni and Lectrides varians (Trichoptera: Leptoceridae), persist under these conditions. Both utilize litter as food, but have different feeding strategies. The more abundant L. darlingtoni ingests organic and microbial material from leaf surfaces, whereas L. varians is a leaf shredder.3. Larval processing budgets based on laboratory and fleid experiments indicated that L. variant has a greater impact on litter decomposition rates than L. darlingtoni. However, because of low density, low oxygen concentrations in pools during summer, and rapid flushing of litter from pools once flow recommences. L. variaus larvae process a small proportion of the total litter input.
Emergence and dynamics of cyclopoid copepods in an unpredictable environment
Authors: WYNGAARD GRACE A. , TAYLOR BARBARA E. , MAHONEY DIANE L. 
Published: May 2006

SUMMARY.
1. We studied species composition, abundance and population dynamics of cyclopoid copepods emerging from dormancy from the sediments of a temporary pond in South Carolina in 1985, 1988 and 1989. During a drought in 1988–89, the maximum hydroperiod was 19 days; in 1985 and late 1989‐early 1990, the hydroperiods were 57 and 118 days. We also report on species present in 1984 and 1987, two years that had longer hydroperiods, and on abundance of cyclopoids in 1984.2. Within a day after standing water appeared, fourth‐instar copepodids of Diacydops haueri and D. crassicaudis brachycercus became active. These two species appeared every time the pond filled in winter, spring, or autumn. Other species, including Acanthocyclops vernalis, were usually not collected until weeks or months after the pond filled. Because the times and durations of fillings were extremely variable, species composition differed among years, with the most species (eleven) appearing in 1984, the year with the longest hydroperiod.3. The abundances of emerging Diacydops were much lower in 1988 and 1989 (range of means from seven fillings in spring and autumn: 675–7382 animals m−2) than 1985 (range of means from three fillings in winter: 26,037–107,418 animals m−2). Low abundances of emerging animals could have been caused by poor survival of dormant animals, poor production during preceding seasons, or incomplete emergence of the dormant populations.4. Substrate samples from the dry pond were collected in spring, summer, and autumn 1988 and winter 1989 to measure emergence of the cyclopoids in laboratory incubations. Population densities of emerging animals were much lower in 1988 and 1989 (range of means from seven experiments: 0–120 animals m−2 over the first 3 days) than in similar experiments in 1984 (Taylor & Mahoney, 1990, means from two experiments: 3630 and 6890 animals m−2).5. Despite the low abundance of animals emerging from dormancy in late 1989, the cyclopoid populations in 1990 reached similar densities of copepodids (104−‐105 animals m−2) to those reached in 1984 and 1985. These results suggest that short generation time and high reproductive capacity permit rapid recovery from population reductions.
Consequences of pH measurement errors
Authors: HOENICKE RAINER , STAPANIAN MARTIN A. , ARENT LORI J. , METCALF RICHARD C. 
Published: May 2006

SUMMARY.
1. The pH range over which the effects of acidification on freshwater organisms become apparent may be quite narrow, in some cases less than half a pH unit. Therefore, accurate measurement is important, particularly in dilute surface waters near the biologically critical threshold of hydrogen ion activity.2. A hypothetical example based on data from two species of fish illustrates the potential errors in predicting mean mortality when pH is measured by probes of varying accuracies, placing our results into an ecosystem management perspective. For a given error, there will be greater uncertainty in predicting mean mortality for species sensitive to increased hydrogen ion activity than for more tolerant species.3. We review field pH measurement errors, and present unique laboratory (measurements at 1°C and under argon) and field comparisons of current instruments used for continuous, in situ pH monitoring, including the only instrument comparison in low conductivity waters during snow melt. Four operator or sampler‐caused measurement errors and three electrode‐caused pH measurement errors are illustrated with data from four common types of pH probes and meters.4. Studies providing no confidence intervals for a set of pH measurements due to the lack of rigorous quality control and assurance procedures are of limited quantitative value to future investigators attempting to analyse temporal trends of surface water acidification. Management and policy decision attempts will remain seriously hampered until more interpretable results are routinely generated.
An experimental study of the effects of predatory fish on macroinvertebrates in a Hong Kong stream
Authors: DUDGEON* DAVID 
Published: May 2006

SUMMARY.
1. Predation upon macroinvertebrates by the loach Oreonectes platycephalus Günther (Cobitidae) was studied using predator inclusion/exclusion cages in a series of pools along a Hong Kong stream. Treatments employed were predator exclusion, medium (approximately natural) predator densities (1 fish cage−1) and high predator densities (2 fish cage−1). Macroinvertebrate abundance in cages was monitored after 2 and 4‐weeks exposure to predators.2. The presence of fish was associated with significant declines in the total numbers of macroinvertebrates colonizing cages. However, taxa were influenced differently, with mayflies decreasing by a factor of two while the more mobile shrimps (Atyidae) were unaffected. Chironomid abundance (largely Chironominae) was unaffected by predator density and increased in week 4. Detritus acted as a confounding variable at this time because chironomid abundance was significantly correlated with the weight of accumulated detritus in cages.3. While invertebrates were more abundant in cages lacking fish, there were no fewer invertebrates in cages with 2 fish than with 1 fish. This may indicate the presence of secure refuges among substrates in the cages, preventing the additional fish from depleting prey further, or a lack of precision of methods due to natural variations in prey densities and spatial patchiness.4. No significant effects of predators on relative prey abundance or species richness were detected.5. The impact of predation on prey abundance weakened on week 4, perhaps due to extra refuges among the accumulated detritus. However, drying of the stream increased fish densities in pools so that cages may have become zones of relative safety that were colonized readily by macroinvertebrates. This result highlights the need for year‐round investigations to quantify predation effects in Hong Kong's seasonal tropical climate.
Competition, survivorship and growth in macrophyte communities
Authors: WILSON SCOTT D. , KEDDY PAUL A. 
Published: May 2006

SUMMARY.
1. Transplant experiments tested the proposition that the intensity of competition within macrophyte communities varies with standing crop in a freshwater marsh in Ontario, Canada.2. Transplants of three species (Carex lasiocarpa, Juncus brachycephalus, Scripus validus) were grown at sixty‐six locations chosen to represent a range of standing crop values. At each location, transplants were grown in plots with all neighbours removed and in adjacent plots with all neighbours present.3. The effect of neighbours on transplant growth did not vary with standing crop, soil, or water depth, with the exception of one species which was most suppressed by neighbours in shallow water. In contrast, the effect of neighbours on the survivorship of transplants was greatest on organic soils supporting high values of standing crop in shallow water, and least on mineral soils supporting low values of standing crop in deeper water.4. The results indicated that establishment and survivorship of vegetative propagules was most likely to be affected by neighbours in shallow water, but that the growth of established plants was not influenced by neighbours anywhere. Growth results corroborate earlier findings that competition has little effect on aquatic macrophytes.
The distribution of chlorophylls, carotenoids and their breakdown products in Lake Kinneret (Israel) sediments
Authors: YACOBI Y.Z. , MANTOURA R.F.C. , LLEWELLYN C.A. 
Published: May 2006

SUMMARY.
1. The sedimentary distribution of chlorophylls, carotenoids and their breakdown products following the winter‐spring bloom of the dinoflagellate Peridinium gatunense in Lake Kinneret was determined both spatially and vertically within the sediments, using high‐pressure liquid chromatography (HPLC).2. All four stations (epilimnic, oxic St. J (depth = 8m) and D (12m) and hypolimnic, anoxic St. F (21 m) A (41 m) were characterized by the presence of chlorophyll a (chl‐a) chl‐b, chl‐c, phaeophytins a (ph'tin‐a) and b, phaeophorbide a (ph'bide‐a) and lutein, fucoxanthin, diatoxanthin and β‐carotene together with spectrally similar, but HPLC‐resolved, breakdown products in the surface sediments. The central deep station A (41 m), which is seasonally anoxic, trapped and preserved significantly more pigments (e.g. chl‐a= 16.35 μg g−1 organic matter) than the more erosive, oxic littoral stations (chl‐a= 1.10 and 0.76μg g−l OM at St. D and J, respectively).3. Whereas it was possible to ascribe the presence of lutein and chl‐b to inputs of green algae and higher plants from the catchment, and fucoxanthin and chl‐c1, c2 to winter diatom blooms (e.g. Melosira granulata), there was a remarkable absence of peridinin and dinoxanthin from sediments, despite the dominance of dinoflagellates in the phytobiomass. This is consistent with the well‐known oxic lability of this epoxy carotenoid in aquatic systems, and indicates efficient breakdown of this dinoflagellate organic matter in the water column, prior to sedimentation.4. Although pigment concentrations all decreased with depths within sediments, lutein and β‐carotene were selectively preserved compared to chl‐a and fucoxanthin which, at 40m depth at St. A, decreased to < 1% of their surface concentrations.
Seasonal trends in river biofilm storage products and electron transport system activity
Authors: BLENKLNSOPP SANDRA A. , GABBOTT PETER A. , FREEMAN CHRISTOPHER , LOCK MAURICE A. 
Published: May 2006

SUMMARY.
1. Glycogen, poly‐beta‐hydroxyalkanoate (PHA) and electron transport system (ETS) activity levels were monitored seasonally in light‐ and dark‐grown biofilms from a North Wales river.2. A spring peak was evident in glycogen, PHA and ETS activity levels per cm2 and per cell, with the exception of PHA per cell, which peaked in the winter.3. There was a seasonal shift in the type of storage product found, perhaps reflecting seasonal changes in carbon sources.4. The light‐grown spring biofilm yielded the greatest amount of bio‐film storage products per cm2. This should be taken into account during caloric studies of river biofilms as a food source for grazing invertebrates.5. A model is presented of factors influencing storage product deposition in river biofilms. The thickness and cell packing of river biofilms should be noted in future studies. Storage product deposition can occur deep within thick biofilms, irrespective of the river water chemistry.