bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stonefly predation along a hydraulic gradient: a field test of the harsh—benign hypothesis
Authors: PECKARSKY BARBARA L. , HORN STEVEN C. , STATZNER BERNHARD 
Published: May 2006

SUMMARY. 1. Microhabitat preferences of predatory stoneflies and four prey taxa were assessed by taking benthic samples along a hydraulic gradient in a Black Forest stream in West Germany. Densities of predator and prey species were estimated at twenty‐one hydraulic regimes.2. Enclosures containing the stonefly, Dinocras cephalotes, and control cages with no predators were placed in the substrate at hydraulic regimes favourable and unfavourable to predators. Cages received initial prey communities that were obtained from benthic samples taken at hydraulic regimes matching those intended for each cage.3. Population densities of the two most numerically important prey taxa, the mayfly. Baetis rhodani, and the Chironomidae, were reduced in the presence of Dinocras, but only when enclosures were placed in the hydraulic regimes favourable to the predator. Thus, predation effects increased as the hydraulic regime became more benign to the predators.4. Densities of two other prey species rare in the diets of Dinocras (Hydropsyche instabilis and Gammarus fossarum) were generally unaffected by predators regardless of the hydraulic regime.5. These data provide support for the hypothesis that perception of the abiotic regime as harsh or benign to predators is a good predictor of predator impact on densities of preferred prey species. In harsher abiotic regimes, impact will be low, while impact will be high in benign abiotic regimes.
Photosynthate partitioning in Antarctic freshwater phytoplankton: in situ incubations
Authors: HAWES IAN 
Published: May 2006

SUMMARY. 1. The distribution of 14C‐labelled photosynthate by phytoplankton in Sombre Lake, Antarctica, was measured during the spring/ summer period in 1987–88.2. Protein was the principal product of low‐light photosynthesis, with the proportion of polysaccharide and lipid increasing at higher radiation fluxes. Storage polysaccharides were mobilized during darkness to fuel continued protein synthesis.3. Maximum rates of protein synthesis and total photosynthesis were attained immediately prior to loss of ice cover, when algal biomass (as chlorophyll‐a) was decreasing. Minimum rale of protein synthesis was coincident with maximum biomass.4. An increase in loss rates as the growing season progresses is postulated to explain the lack of coupling between biomass changes and photosynthesis.
Zooplankton distribution in relation to turbidity and related environmental gradients in a large subtropical reservoir: patterns and implications
Authors: HART R. C. 
Published: May 2006

SUMMARY.

A marked gradient in water transparency along the 75 km longitudinal axis of Lake le Roux, a fjord‐like reservoir on the Orange River, South Africa, was consistently evident over several years. On average, Secchi depth transparency doubled from approximately 18 cm at the turbid upper end (which is fed by sediment‐laden Orange River water discharged from Lake Verwoerd), to 33 cm near the dam wall. A variety of changes in abiotic limn logical attributes (temperature, light attenuation, suspended solids and nutrient levels, etc.), and in the abundance and composition of planktonic biota accompany, and may be imposed by, this turbidity gradient.
On average, phytoplankton abundance (assessed as chlorophyll content), and total crustacean zooplankton biomass (per unit volume) were lowest at the very top of the lake, but reached maximal values within 15 km ‘downstream’, reflecting the rapid development of plankton. These variables subsequently declined downstream, in contrast to the apparent improvement in conditions for planktonic existence (increasing water transparency, longer water residence time, etc.).
The composition of crustacean zooplankton varied along the length of the reservoir. Both seasonal and inter‐annual differences were evident. On average, however, cladocerans (Daphnia, Moina), despite their r‐selected attributes, were especially sparse in the more turbid, uppermost reaches, where advective effects of river inflows were most pronounced. The large predatory copepod Lovenula was surprisingly most abundant in this region, where potential planktonic curstacean prey was scarce. The attainment of maximal zooplankton standing slocks some 15 km downstream was attributable to the proliferation particularly of the herbivorous copepod Metadiaptomus, along with minor increases in several ctadoceran components. The latter continued to increase downstream, in line with declining turbidity, although Daphnia and Moina reached their respective abundance maxima in central and lower reaches of the reservoir, reflecting slight disparities in response to turbidity or related gradients. By contrast.
Quantifying the impact of periphytic algae on nutrient availability for phytoplankton
Authors: HANSSON LARS‐ANDERS 
Published: May 2006

SUMMARY.

Recent laboratory studies demonstrate that periphytic algae growing on the sediment surface reduce nutrient availability in the overlying water. Consequently, periphytic algae may competitively reduce growth of phytoplankton.
The aim of this study was to quantify the competitive impact of sediment‐attached periphytic algae on phytoplankton in the presence of all other factors simultaneously affecting nutrient dynamics in natural systems.
In enclosure experiments, performed in three lakes of different productivity, the periphytic algal biomass was manipulated. When compared to enclosures with high biomass of periphytic algae, those with reduced biomass showed an increase in total phosphorus concentration in the water of 32–44%. Extrapolation of the experimental results to whole lakes predicts an increase in original total phosphorus concentration of between 1.5% and 8.0%. According to existing regressions between total phosphorus and phytoplankton chlorophyll, the potential increase in original phytoplankton biomass will be between 2.5% and 12.6%.
With respect to the shallow parts of lakes, my results support the conclusions revealed from laboratory studies that periphytic algae have a significant impact on the phosphorus concentration in the overlying water. However, when considering whole‐lake dynamics, the competitive impact of periphytic algae on phytoplankton biomass development is probably of minor importance.
Rather, the main competitive advantage of growing on the sediment surface, compared to in the water, may be the exclusive access to nutrients in the sediment.
Successional changes in the soft‐water macrophyte vegetation of (sub)atlantic, sandy, lowland regions during this century
Authors: ARTS G. H. P. , VAN DER VELDE G. , ROELOFS J. G. M. , VAN SWAAY C. A. M. 
Published: May 2006

SUMMARY.

Considerable changes in macrophyte vegetation can be noticed in 146 originally soft waters, when data on the recent aquatic vegetation are compared with historical information from the period 1900–60. Changes in nutrient status (N, P and C) and accumulation of organic material can be regarded as the operative factors.
The processes observed in soft waters are acidification, eutrophication and water hardening. Which process dominates depends on the type of soft water.
Acidification as well as eutrophication of water bodies may ultimately result in the total disappearance of all aquatic macrophytes, with the exception of the floating‐leaved nymphaeids Nymphaea alba L. and Nuphar lutea (L.) Sm. Observed successional stages are described and summarized.
Spatial distribution, seston removal, and potential competitive interactions of the bivalves Corbicula fluminea and Elliptio complanata, in a coastal plain stream
Authors: LEFF LAURA G. , BURCH JARRETT L. , McARTHUR J. VAUN 
Published: May 2006

SUMMARY.

Within the past 10 years the introduced exotic bivalve, Corbicula fluminea, has spread from the Savannah River through a riverine swamp into a third‐order blackwater tributary on the Savannah River Site (SRS). We examined the effects of this invasion on a native bivalve, Elliptio cornplanata, and on seston concentration in the stream.
Corbicula fluminea has not yet colonized the entire stream and its distribution limit is coincident with the occurrence of gravel beds.
Corbicula fluminea appears to cause localized reduction of seston concentration and may rapidly clear the sediment boundary layer of food. There was no evidence of a negative impact on the distribution of the native bivalve in spite of high measured rates of water clearance by C. fluminea.
Secondary production of chironomid communities in insecticide‐treated and untreated headwater streams
Authors: LUGTHART GARRIT J. , WALLACE J. BRUCE , HURYN ALEXANDER D. 
Published: May 2006

SUMMARY.

Production of chironomid communities of three first order, Appalachian Mountain streams was estimated and the effects of an insecticide‐induced disturbance on chironomid production was examined.
Annual production of non‐Tanypodinae chironomids in the streams during the first study year (no treatment) ranged from 1366 to 3636 mg m−2, while production of Tanypodinae chironomids ranged from 48 to 116 mg m −2. Production/biomass ratios ranged between 19 and 23 for non‐Tanypodinae and from 6 to 7 for Tanypodinae chironomids.
Insecticide applications resulted in significantly lower chironomid densities and biomass in the treated stream relative to the pretreatment year and reference stream. Annual production of non‐Tanypodinae (703 mg m−2) and Tanypodinae (32 mg m −2) chironomids in the treated stream decreased by 64% and 67%, respectively, compared with the pretreatment year. In contrast, production of non‐Tanypodinae (2084 mg m−2) increased by 34% and production of Tanypodinae (96 mg m−2) by 57% in the reference stream.
Effect of predatory fish presence on habitat use and diel movement of the stream amphipod, Gammarus minus
Authors: HOLOMUZKI JOSEPH R. , HOYLE JOHN D. 
Published: May 2006

SUMMARY.

We examined how the presence of predatory fish affected macro—and microhabitat use and movement patterns of the amphipod, Gammarus minus Say, in a second order stream.
Among macrohabitats, amphipods were consistently more abundant in runs than in pools. Densities in pools were low regardless of fish presence, whereas low densities in runs were correlated with fish presence. Siltation and the lack of coarse substrate particles probably accounted for the scarcity of G. minus in pools. Among microhabitats, G. minus was more abundant in leaf litter and gravel than in silt/sand substrates. Fish presence did not affect microhabitat use in the field. Laboratory manipulations showed, however, that predation rates by green sunfish (Lepomis cyanellus Rafinesque) were significantly lower on amphipods in leaf litter than in other microhabitats.
Most movement by G. minus in runs occurred at night and was directed downstream. In the laboratory, amphipods significantly reduced swimming activity at night in response to water conditioned with green sunfish. In the field, however, amphipods were only slightly less active in runs at night when exposed to chemical cues of confined green sunfish. The distribution of amphipods in streams is influenced by the presence of fish, but chemical cues alone may not be important in triggering predator avoidance behaviours in nature.
Effect of Anabaena flos‐aquae on the abilities of Daphnia and Keratella to feed and reproduce on unicellular algae
Authors: GILBERT JOHN J. , DURAND MARK W. 
Published: May 2006

SUMMARY.

This study tests the hypothesis that the filamentous cyanobacterium, Anabaena flos‐aquae, inhibits Daphnia's ability to feed and reproduce on unicellular algae more than it does Keratella's. Double‐label radiotracer experiments using whole and sonieally disrupted Anabaena filaments showed that even low concentrations of Anabaena (5 × 103 cells ml−1) inhibited the abilities of Daphnia pulex and D. galeata mendotae to feed on Chlamydomonas and that this inhibition was due to both mechanical interference with feeding and increased food availability. A single‐label radiotracer experiment showed that Anabaena (5 × 103 and 2 × 104 cells ml−l) reduced the abilities of neonate, juvenile, and adult D. pulex to feed on Chlamydomonas but had a much more pronounced effect on adults.
Single‐label radiotracer experiments using screened (25 μm mesh) and unscreened suspensions of whole Anabaena filaments showed that only very high concentrations of Anabaena (105 cells ml−1) reduced the ability of Keratella cochlearis to feed on Cryptomonas and that this inhibition probably was due to mechanical interference with feeding, since Keratella ate Anabaena extremely inefficiently ‐ especially when single cells and short filaments were removed by screening.
Experiments comparing the survivorship and fecundity of individuals fed Anabaena, Chlamydomonas, or no food showed that the Anabaena was not toxic to either Keratella or D. galeata mendotae, was not utilized by Keratella, and was utilized by Daphnia, although not as well as Chlamydomonas was.
Anabaena (5 × 103 or 104 cells ml−1) did not affect, or slightly increased, the population growth rate (rm) of K. cochlearis on Cryptomonas, while it substantially increased that of D. pulex, Duphnia's ability to utilize Anabaena probably more than offset its reduced ability to feed on Cryptomonas. The presence of cyanobacterial filaments in natural plankton communities could adversely affect Daphnia and decrease its ability to competitively suppress Keratella and other rotifers if the filaments were of little nutritional value to the Daphnia, greatly interfered
Genetic variation and reproductive mode in populations of Simocephalus vetulus (Branchiopoda: Cladocera) from the East Midlands of England
Authors: WARD* ROBERT D. , TOLLIT ROSALIND M. , BICKERTON MELANIE A. 
Published: May 2006

SUMMARY.
1. Five populations of the cladoceran Simocephalus vetulus (O. F. Muller) examined by enzyme electrophoresis at four to five loci revealed high levels of genetic variation.2. The one intermittent population had genotype frequencies in Hardy Weinberg equilibrium, the three permanent populations showed deviations from equilibrium of varying magnitude. The fifth population was fixed for a single clone, and was possibly recently derived from a single ephippial hatchling.3. Laboratory breeding experiments confirmed that this species is a cyclic parthenogen.
Population dynamics and production of the pelagic amphipod Hyalella montezuma in a thermally constant system
Authors: DEHDASHTI B. , BLINN DEAN W. 
Published: May 2006

SUMMARY.
1. The population dynamics and annual production of the multivoltine. pelagic amphipod Hyalella montezuma were studied over a 3‐year period in the thermally constant environment of Montezuma Well. Arizona.2. H. montezuma showed two maxima which coincided with spring and autumn phytoplankton maxima. Juveniles comprised over 85% of the population in the pelagic zone compared to 37% in the littoral vegetation and there were significantly more females in the littoral vegetation. It appears that juvenile and adult H. montezuma show different habitat preferences.3. Total annual mean production for H. montezuma calculated by the size frequency method and adjusted for multiple generations, was 357 kg ha−1 yr−1, which is higher than single‐species production estimates reported for most zoobenthic amphipods and multivoltine planktonic crustaceans. Average energy production for H. montezuma was 4640 kJ ha−1 yr−1 in the pelagic zone and 1072 kJ ha−1 yr−1 in the littoral vegetation.4. Average cohort P/B̄ ratios for H. montezuma were higher in the pelagic zone (5.5) than in the litttoral vegetation (3.7). Juveniles had higher cohort PB̄ ratios than adults in the pelagic zone, while the reverse relationship was true in the littoral vegetation. We propose that different size‐selective predators may contribute to the differences in PB̄ ratios for juveniles and adults in these two habitats.
Consequences of tadpole shrimp predation on mayflies in some Californian ponds
Authors: WALTON WILLIAM E. , TIETZE NOOR S. , MULLA MIR S. 
Published: May 2006

SUMMARY.
1. During two, 1‐month studies, the abundance of mayfly nymphs, Callibaetis californicus Banks, in small ponds that contained the tadpole shrimp, Triops longicaudatus (LeConte), often was significantly lower than in ponds without tadpole shrimps. Mayfly abundance was either positively correlated or not significantly associated with that of predacious insects.2. Larger mayfly nymphs were a greater fraction of the population in ponds with Triops than in ponds without tadpole shrimps. Between 2 and 3 weeks after ponds were flooded, the smallest mayfly nymphs were absent from ponds in which T. longicaudatus densities were >5 individuals per square metre during the summer and >15 individuals per square metre during the autumn.3. In prey‐choice trials, T. longicaudatus consumed predominantly small C. californicus nymphs (mean headwidth ± 1 SD: 0.44 ± 0.05 mm). After encounters with tadpole shrimps, small mayfly nymphs moved relatively shorl distances, were easily overtaken, and were, consequently, more susceptible to tadpole shrimps than larger‐sized nymphs.
Competition between Keratella cochlearis and Daphnia ambigua: effects of temporal patterns of food supply
Authors: MACISAAC HUGH J. , GILBERT JOHN J. 
Published: May 2006

SUMMARY.
1. Population growth rates and relative competitive abilities of the rotifer Keratella cochlearis f. tecta and the small‐bodied cladoceran Daphnia ambigua were studied under different schedules of food addition but equal total food quantity (per 4‐day interval). The initial population growth rate of Keratella was significantly affected by the feeding schedule and by the presence of competitors, while that of Daphnia was affected by neither factor. Population densities of both species tended to increase as the frequency of food addition increased.2. Daphnia suppressed and excluded Keratella from mixed‐species cultures when food was provided intermittently at a high concentration, but it failed to exclude the rotifer when food was provided in a near‐continuous supply at low concentration. Keratella had only a minor suppressive effect on Daphnia in all mixed‐species treatments.3. Starvation experiments indicate that Daphnia is able to withstand food shortages for significantly longer periods of time than Keratella. These and other results indicate that the outcome of interspecific competition between these species may be influenced by me frequency and concentration at which food is supplied. Daphnia ambigua is competitively superior to K. cochlearis when food is concentrated or ‘pulsed’, but much less so when ambient food levels are chronically low. Patterns of food availability may have important effects in determining the relative abundance of rotifers and small cladocerans in natural zooplankton communities.
Micro‐environmental characteristics of filamentous algal communities in flowing freshwaters
Authors: DODDS WALTER K. 
Published: May 2006

SUMMARY.
1. Filamentous algae in flowing freshwaters can represent a spatially and temporally distinct sub‐habitat for epiphytic diatom communities. This sub‐habitat is described in a low discharge, spring‐fed stream with extensive filamentous green algal mats, and in a tuft of Cladophora glomerata (L.) Kützing from a large river.2. Oxygen micro‐electrodes, a thermistor current velocity probe, a standard pH probe and water chemistry were employed to assess spatial heterogeneity. Temporal patterns of epiphyte colonization were evaluated on filamentous artificial substrates.3. There were steep spatial gradients in the low discharge stream. At mid‐day, O2 ranged from 0–1.5 times air‐saturated O2 concentrations, pH varied from 7.25–8.0, and current velocity spanned 0–0.5 m s−1. Areas near the surface of algal mats had high O2, pH and current velocity. These patterns were correlated with epiphyte community structure.4. In the interior of C. glomerata tufts O2 concentration was raised and current velocity depressed compared to the surrounding water, even when external current velocity was as high as 0.4 m s−1.5. After thirty‐five days of colonization of artificial substrate in the low discharge environment, epiphyte communities were similar to those on filamentous atgae. Epiphyte diversity on artificial substrates subsequently decreased compared to natural substrates as did the similarity between the types on substrates, suggesting that microscale renewal of epiphyte habitat (growth of filamentous algae) maintains high epiphytic diversity.
Seasonally and spatial distribution of the ostracods of Lake Zwai, Ethiopia (Crustacea: Ostracoda)
Authors: MARTENS KOEN , TUDORANCEA CLAUDIU 
Published: May 2006

SUMMARY.
1. Quantitative benthic samples were collected monthly between June 1984 and May 1985 from seven stations at various depths in Lake Zwai, one of the Ethiopian Rift Valley lakes, situated in the northern part of the Rift Valley. The most common species of ostracods were Limnocythere thomasi thomasi Martens (a subspecies endemic to Lake Zwai), Gomphocythere angutata Lowndes (common in, but restricted to. East Africa) and Darwinula stevensoni (Brady & Robertson) (cosmopolitan).2. Absolute densities of all species varied considerably over the year. In all stations, there were population peaks during the two dry seasons, followed by as yet unexplained population crashes during the short and the long rains.3. The three common species had different habitat preferences. Darwinula stevensoni avoids parts of the lake where temperatures rise high and both G. angulata and L. thomasi had a preference for sheltered habitats close to vegetation and/or for a specific grain size of the sediment (300–350 μm).
Population dynamics and production of Daphnia hyalina and Bosmina longirostris in a shallow, eutrophic reservoir
Authors: MASON C. F. , ABDUL‐HUSSEIN M. M. 
Published: May 2006

SUMMARY.
1. The population densities, dynamics and production of Daphnia hyalina and Bosmina longirostris were studied over a 2‐year period in a shallow eutrophic reservoir in eastern England. The diet of the two species was assessed and their ecology was compared in relation to environmental factors.2. Daphnia hyalina was characterized by small overall body size, probably due to heavy size‐selective predation by fish. The first generation produced from the overwintering population appeared in April and Depopulation peaked in late spring and early summer. Adult survival was poor. Peak egg production varied between years, while mean brood size fell in summer probably due to food limitation during the cyanobacterial bloom. At this time selection for individual algal species was high and many guts were empty. Reproductive ratios were inversely related to population density. Bosmina longirostris exhibited a similar annual cycle.3. Patterns of production were very different in the 2 years in D. hyalina. In 1981 production was high from August to early October, but in 1982 the peak was in spring. Annual production was 32.4 g C m−2 in 1981 and 13.3 g C m−2 in 1982. In 1981 B. longirostris production peaked in spring and late summer; in 1982 there was a high production in summer only. Annual production was 3.2 g C m−2 in 1981 and 2.2 g Cm−2 in 1982.4. The number of adult D. hyalina was highly correlated with water temperature and total phytoplankton biomass, but these were negatively correlated with the number of eggs, mean brood size and instantaneous birth rate. In contrast, clutch size of B. longirostris was positively correlated with water temperature while birth rate was positively correlated with both temperature and phytoplankton biomass. The biomass of both species was positively related to total phytoplankton biomass, but neither relationship explained much of the variation in zooplankton biomass.5. The significance of the observations on plankton in terms of managing the water quality in eutrophic reservoirs is discussed.