bluuebunny/crossref_metadata_2025_split huggingface dataset:
A comparative study of colonization by benthos in a lake and its outflowing stream
Authors: Quinn  
Published: March 2003

1. The patterns of colonization of littoral benthos onto hard substrata on an exposed and a sheltered shore of Lake Purrumbete in Victoria, Australia, and the riffles of its outflow stream (Curdies River) were examined experimentally in winter and summer. The common taxa in the lake (gastropods, amphipods, isopods, planarians, ostracods) also occurred in the stream, although they were not abundant. The stream fauna was dominated by insects.2. Defaunated half‐bricks were sampled at each of three sites at the three different locations (exposed shore, sheltered shore, stream) in winter and summer at weekly or biweekly intervals, with natural stones also being sampled during the colonization period. Colonization patterns of individual taxa which occurred in both the lake and stream, and stream‐only taxa, were compared using ANOVA, and the changes in the assemblage through time and between locations were analysed with non‐metric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM).3. Colonization in the lake was very rapid, with species richness and assemblage composition on bricks after just one day matching that of natural stones. Colonization in the stream was slower, the assemblage composition not matching natural stones after 42 days in winter but being comparable after 28 days in summer. There was considerable species turnover during colonization in the stream, but little turnover in the lake, with most common taxa back after one day. There was little difference between the two lake shores in colonization patterns.4. Taxa that occurred in both lake and stream showed broadly similar patterns of colonization, with early occupancy at high densities. In contrast, stream insects showed a variety of colonization strategies.5. These results indicate that rates and patterns of colonization on to hard substrata are quite different in Lake Purrumbete compared with its outflowing stream. The rapid colonization in this lake indicates great mobility for much of the fauna on hard substrata, possibly by swimming, benthic crawling or passive drift (even attached to floating vegetation). This may be an appropriate strategy in lake littoral zones where the amount of inhabitable hard substrata and accompanying food resources may be limited.
Role of nutrients and zooplankton in regulation of phytoplankton in Flathead Lake (Montana, U.S.A.), a large oligotrophic lake
Authors: Spencer Craig N. , Ellis And Bonnie K. 
Published: March 2003

1. Increased primary production in Flathead Lake during the 1980s has been variously attributed to increased nutrient loadings and/or decreases in zooplankton abundance resulting from the introduction of Mysis relicta. In order to assess the importance of these two factors in regulating the phytoplankton community in Flathead Lake, we manipulated zooplankton abundance and nutrient availability in a series of 5‐day enclosure experiments. 2. Chlorophyll a levels were stimulated by simultaneous addition of nitrogen and phosphorus. At ambient nutrient levels, alteration of zooplankton density had no effect on chlorophyll a levels. Top‐down control through zooplankton grazing could only be demonstrated in treatments supplemented with nutrients. Under these conditions, there was a significant negative correlation between zooplankton abundance and final chlorophyll a levels. 3. These results suggest that the phytoplankton community in Flathead Lake is regulated primarily by bottom‐up controls. Consequently, future management activities aimed at preventing further increases in algal growth in the lake should focus on nutrient abatement. Alteration of the upper trophic levels does not appear to have significantly affected phytoplankton abundance in the lake. Should nutrient levels increase in the future, then top‐down controls may become more important. 4. A conceptual model is presented illustrating the relative importance of top‐down and bottom‐up controls across a trophic gradient.
The relative importance of top‐down and bottom‐up control of phytoplankton in a shallow macrophyte‐dominated lake
Authors: Stephen Debbie , Brian  ,   And GEOFF PHILLIPS
Published: March 2003

1. Mechanisms stabilizing the plant‐dominated clear‐water state were investigated in Little Mere, U.K. Replicated, factorial, mesocosm experiments, carried out in 1995 and 1996, were designed to investigate the relative importance of top‐down (zooplankton grazing) and bottom‐up (nitrogen‐limitation) control in limiting algal growth, and the role of macrophytes in these processes. Treatments included increased salinity (1995) and sticklebacks (1996) to reduce zooplankton numbers, weekly nitrate additions and removal of macrophytes.2. Contrary to the results of other studies, submerged plants did not reduce nitrate concentrations. Owing to the high stickleback density in the enclosures with fish, macrophytes did not provide a refuge for zooplankton during the experiment. In Little Mere, however, where fish densities are lower, macrophytes probably play a key role in maintaining clear water by providing refuge for pelagic zooplankton and habitat for attached Cladocera.3. Phytoplankton in Little Mere was not nitrogen‐ (N) limited during the growing season. Although nitrogen availability sets a maximum potential phytoplankton biomass it was not realized owing to control by zooplankton grazing.
The relationship between nutrients and trophic‐level biomass in turbid tropical ponds
Authors: Sarnelle Orlando , Cooper Scott D. , Wiseman Sheila , Mavuti Kenneth M. 
Published: March 2003

1. The total phosphorus–algal biomass relationship from a set of turbid tropical ponds in Kenya was compared with predictions derived from surveys of temperate and subtropical lakes. Despite high concentrations of total phosphorus (TP) (up to 797 μg L–1) and inorganic turbidity (up to 800 mg L–1), the log–log relationship between algal biomass and TP was steeper than expected.2. No evidence of nitrogen limitation was found at high TP, and total nitrogen (TN):TP ratios were higher than in lakes with similar TP levels studied previously. High TN:TP ratios may be a consequence of excretion by cattle into the ponds, a nutrient source characterized by a high ratio of available N to available P.3. Despite extremely high turbidity, the ratio of mixed layer depth to euphotic depth was generally low because these ponds are shallow (≤ 2 m), and was not related to algal yield. A positive relationship was also found between TP and zooplankton biomass, and between TP and the density of the zooplanktivorous bug, Anisops. In contrast, no relationship was found between fish biomass and TP, algal biomass or zooplankton biomass.
Geographical variation in Japan in egg development of the mayfly,Ephoron shigae(Ephemeroptera: Polymitarcyidae)
Authors: Watanabe Naoshi C. 
Published: March 2003

1. The effect of temperature on embryonic development was compared in four populations, two bisexual and two unisexual, of Ephoron shigae, including one each near the northern and southern periphery of the species range in Japan.2. Eggs from every population were chilled at 4, 8 or 12 °C for diapause development after 50 days at 20 °C for pre‐diapause development (experiment I). Some eggs hatched during chilling at 8 °C or 12 °C, whereas no eggs hatched at 4 °C. The rate of hatching in a given condition of chilling was higher for the eggs from warmer winter environments.3. Chilling at 4 or 8 °C effectively facilitated diapause development. Chilling at 12 °C was, in general, not so effective, but relatively effective for the eggs from warmer winter environments.4. Eggs were incubated at 8, 12, 15 or 20 °C after chilling at 4 °C to examine the effect of temperature on post‐diapause development (experiment II). The eggs incubated at higher temperature after chilling hatched quicker and more synchronously and had higher hatching success.5. The relationship between temperature and the days required for hatching after chilling was well described by the power function. There was no significant difference in the slope of the regression lines (i.e. temperature dependency) among local populations. However, a longer time was required for hatching at a given temperature for the population from the colder winter environment.6. There was no detectable difference in the observed intraspecific variations between unisexual and bisexual populations.
Relationships between DOC concentration and epilithon stable isotopes in boreal lakes
Authors: France R. L. 
Published: March 2003

1. Littoral biota in boreal lakes are known to assimilate epilithon. Being able to predict the stable isotopic composition of these alga will help to identify those systems in which δ13C and δ15N analysis can be used in foodweb investigations of allochthony and biomagnification.2. In a survey of 15 boreal lakes, the concentration of dissolved organic carbon (DOC) explained 76% of the variation in epilithon δ13C, and 86% of the variation in epilithon δ15N.3. Because both δ13C and δ15N values were depressed and similar to terrestrial values in humic (high DOC) lakes, it will be more difficult to successfully employ stable isotopic techniques for estimating allochthony in such systems. Lower δ15N values in humic lakes also indicate that trophic positions estimated by stable isotopes are not directly comparable to those of similar biota inhabiting clearwater lakes, unless autochthonous baseline corrections are made.
Empirical relationships between profundal macroinvertebrate biomass and environmental variables in boreal lakes of Alberta, Canada
Authors: Dinsmore W. Paul , Scrimgeour Garry J. , Prepas Ellie E. 
Published: March 2003

1. We empirically modelled profundal macroinvertebrate biomass (PMB) from collections of macroinvertebrates and a suite of trophic, water chemistry and morphometric variables from 26 lakes located within the Boreal Mixedwood and Boreal Subarctic ecoregions of Alberta, Canada.2. Hypolimnetic dissolved oxygen (DO) concentrations (mg L−1) explained 37% of the variance in PMB ((g m−2)0.1) as a quadratic function, whereas water temperature (°C) explained 23% of variance in a linear relationship.3. In contrast with other studies based on oligotrophic systems, indirect indicators of food availability (i.e. chlorophyll a and total phosphorus concentrations and Secchi depth) were not significant predictors of PMB in this study.4. The predictive power of our models may be improved by obtaining more frequent (seasonal) estimates of PMB and hypolimnetic DO concentration and by quantifying biotic factors such as competition, predation, life history phenologies and recruitment success.
Seasonal and interannual variability of plankton carbon isotope ratios in a subarctic lake
Authors: Gu B. , Alexander V. , Schell D. M. 
Published: March 2003

1. Carbon isotope ratios (δ13CD) of a herbivorous zooplankter, Daphnia middendorfiana and several environmental variables were investigated during four annual production cycles (1988–92) in Smith Lake, Alaska to determine factors that affect the seasonal and interannual variability of δ13CD.2. δ13CD varied from −44.7 to −31.5 ppt and was significantly correlated with Chl a (r = 0.66, P = 0.0001), weakly correlated with CO2(aq) (r = 0.31, P = 0.07) and uncorrelated with δ13CDIC (r = 0.10, P = 0.70). Carbon isotope fractionation was minimal when Chl a appeared to be optimal. The largest 13C fractionation was associated with the lowest Chl a during early and mid winter periods.3. δ13CD was also significantly correlated with water temperature (r = 0.480, P = 0.0001) and photoperiod (r = 0.62, P = 0.0001), probably suggesting a critical role of physical forcing, particularly solar energy input, in affecting algal photosynthesis and δ13CD in this subarctic lake.4. There was a large interannual variability of δ13CD among ice‐cover periods which was partly explained by interwinter differences in the amount of snowfall that affected the flux of solar irradiance to the ice‐covered lake.5. Other explanations for δ13CD variability such as species succession, changes in algal cell size and differential use of CO2(aq) and HCO3– were also considered, but cannot account for the observations reported here.
Effects of hydrological variation and planktivorous competition on macroinvertebrate community structure in experimental billabongs
Authors: Nielsen D. L. , Hillman T. J. , Smith F. J. 
Published: March 2003

1. To study two factors which are predicted as causing changes to community structure in cut‐off meanders (colloquially known in Australia as billabongs, a term of aboriginal origin), 16 experimental billabongs were constructed. These were designed to test two hypotheses: (a) that the structure of macrophyte and invertebrate communities within billabongs is altered by changing the pattern of flooding; and (b) that the presence of small planktivorous fish alters invertebrate community structure and diversity within billabongs.2. An increase in the duration of flooding seems to favour animals better adapted to a greater availability of macrophyte habitat. Changing the seasonality of flooding resulted in prolonging of the time water was available over the summer months.3. The presence of a planktivorous fish appears to affect macroinvertebrate communities through competition with other planktivores. Variable top‐down pressure may create differing successional patterns and ultimately different communities at lower trophic levels.
Effects of prey abundance and light intensity on the mixotrophic chrysophyte Poterioochromonas malhamensis from a mesotrophic lake
Authors: Holen Dale A. 
Published: March 2003

1. Previous studies of mixotrophy in the flagellate Poterioochromonas malhamensis (Chrysophyceae) were performed on strains that had been in culture for > 30 years. This study aims to compare mixotrophy in a cultured strain with one recently isolated from a mesotrophic lake (Lacawac) in Pennsylvania, U.S.A.2. P. malhamensis from the lake exhibited a nutritional flexibility similar to that of the culture strain, growing phototrophically but inefficiently in comparison to other nutritional modes (growth rate (μ) = 0.015 h−1). Supplementing an inorganic salts medium with 1 mM glucose resulted in a doubling of μ to 0.035 h−1 and 0.033 h−1 in the light and the dark, respectively. Addition of an algal prey, Nannochloris, to the inorganic salts medium increased growth to rates similar to those observed with glucose. Maximum growth of the lake strain, 0.095 h−1, was achieved when bacteria was supplied as food. During growth on bacteria, cellular chlorophyll a (Chl a) decreased from 140 fg cell−1 to 10 fg cell−1 over 22 h when cultured either in the light or dark. In illuminated cultures, cell‐specific Chl a concentration recovered to 185 fg cell−1 after bacteria became limiting.3. In contrast to the cultured strain, however, the lake isolate exhibited an inverse relationship between light intensity and ingestion rate. Calculated grazing rates, based upon the ingestion of fluorescently labeled bacteria, were 3.2, 5.2 and 9.4 bacteria flagellate−1 h−1, for P. malhamensis incubated in high light, low light and darkness, respectively. Phagotrophy is thus influenced by a light regime in this predominately heterotrophic mixotroph.
Influence of lake trophic status on the occurrence of microcystin‐LR in the tissue of pulmonate snails
Authors: Zurawell Ronald W. , Kotak Brian G. , Prepas Ellie E. 
Published: March 2003

1. To assess the influence of lake trophic status on the occurrence of microcystin‐LR (MCLR) in the tissue of resident pulmonate snails, we sampled seven lakes of varying primary productivity in Alberta, Canada. Parameters associated with productivity were measured every 2 weeks from mid‐May through mid‐September 1995. Phytoplankton and resident pulmonate snails were collected and analysed for MCLR concentration via high‐performance liquid chromatography.2. For all species of gastropod (i.e. Lymnaea stagnalis, Helisoma trivolvis and Physa gyrina), the concentration of MCLR in the tissue was correlated (P ≤ 0.03) with toxin in the phytoplankton, but not with extracellular aqueous microcystin (P > 0.28). The concentrations of toxin in the tissues of L. stagnalis and P. gyrina were also correlated with the relative abundance of Microcystis spp. (P < 0.01).3. Given that Microcystis spp. abundance and MCLR concentration within phytoplankton are correlated with indicators of productivity, we conclude that trophic status is important in influencing the occurrence and concentration of MCLR in pulmonate snails.
Growth, production and mortality of two species of Agapetus (Trichoptera: Glossosomatidae) in the Acheron River, south‐east Australia
Authors: Marchant R. , Hehir G. 
Published: March 2003

1. Quantitative samples of Agapetus pontona and Agapetus monticolus larvae were taken at two sites on each of three rivers in the catchment of the Acheron River (i.e. Little River, Steavenson River and Acheron River). Both species were univoltine with A. pontona having a 5–6‐month life cycle (spring to late summer) and A. monticolus a 10‐month life cycle (autumn to early summer).2. Population densities, biomass (B), growth rates and mortality patterns derived from these field data were used to calculate secondary production (P) and turnover (P/B). At each site, these features were measured for the whole of the A. pontona life cycle, but only for the last 3 months of the A. monticolus life cycle.3. Growth rates were highest at the sites on the Little River during summer for both species: 1.8–1.9% dry weight day−1 for A. pontona and 2.0–2.2% dry weight day−1 for A. monticolus. Turnover ratios (P/B) were also highest at the Little River sites: 3.2–6.3 for A. pontona and 1.6–1.9 for A. monticolus. Production was variable and was not significantly different among rivers for A. pontona (28.4–222.1 mg m−2 per 6 months) but was for A. monticolus (70.5–123.8 mg m−2 per 3 months for the Little River compared with 14.8–23.3 mg m−2 at the other sites).4. Two of the rivers were subject to higher levels of rock movement during summer than the third (Little River). It was suggested that the higher growth rates (and turnover ratios) in the Little River were caused by the lower levels of rock movement causing less disruption to the feeding of the larvae.5. Little or no larval mortality of A. pontona was observed at any site. However, mortality occurred between instar 5 and the pupal stage. This varied in a density dependent fashion, suggesting population regulation occurred: the higher the larval density the greater the mortality suffered by the pupae. No such density dependent pattern occurred for the mortality between instar 5 and the pupal stage of A. monticolus.6. The population of A. pontona was not food limited and larval densities were low. Competition appeared to occur for pupation sites. Low and relatively constant discharges during the late summer when A. pontona pupated appeared to provide more predictable conditions than those experienced by A. monticolus in the spring when discharge was very variable resulting in the stranding (and thus death) of pupae above the water line. Such unpredictable conditions would not foster density dependent population regulation via pupal mortality.
Manipulating the intensity of near‐bed turbulence in rivers: effects on benthic invertebrates
Authors: Robson B. J. , Chester E. T. , Davis J. A. 
Published: March 2003

1. Flow conditions were modified over patches of river bed in three rivers in south‐western Australia to determine the effects of turbulence on benthic invertebrate communities.2. Artificial structures to increase downstream turbulence were developed in a laboratory flume. In the field, these increased turbulence intensity by 35% for a 20% reduction in velocity.3. Patches of gravel were placed in each river and turbulence‐generating structures allocated randomly to half of these, creating treatment patches. An acoustic Doppler velocimeter was used to measure flow conditions over both treatment and control patches at several heights above the bed. After 6 weeks, the invertebrate fauna of the gravel patches were sampled to examine the response to modified flow conditions.4. The treatments increased relative turbulence intensity twofold for a reduction in velocity of between 3 and 5 cm s−1, but turbulence intensity was significantly higher in only one of the three rivers.5. There were no significant effects of increased relative turbulence intensity on any aspect of the invertebrate assemblage. This may be a result of the fairly small increase in relative turbulence intensity created during the experiment, the spatial scale of the manipulation or the types of stream community studied.
Where to stay by night and day: Size‐specific and seasonal differences in horizontal and vertical distribution of Chaoborus flavicans larvae
Authors: Voss S. , Mumm H. 
Published: March 2003

1. Data on the distributions of pelagic and benthic Chaoborus flavicans larvae were gathered in 1994 and tested for their agreement with the predator avoidance hypotheses. The development of all Chaoborus life stages, as well as the horizontal and vertical distribution in the four larval instars, was followed from May until October. We expected the largest larvae to dwell deeper by day, thus avoiding predation by visually foraging fish.2. In agreement with this prediction body size increased with daytime depth, and this was true both between and within instars. The migration amplitude consequently increased with larval instar.3. There was also evidence for horizontal migration, mainly in the third but also in the fourth instar.4. Along a horizontal transect with increasing depth, locations with many benthic larvae had fewer pelagic larvae. Oxygen concentration was a good predictor of maximum benthic larval depth for most of the season but failed to predict their distribution in autumn.