Water organism such as zooplankton fish were used quite often as indicators for water quality in connection with chemically toxic substance in water. Several criteria could be used such as LC50, population index, and physiological phenomena. Bioassay that rely on this physiological phenomena was meant to measure the sublethal effect of the suspected toxic substance on the organisms. Further development of sublethal bioassay using filtering rate of Daphnia carinata (Cooley, 1977; McMahon, 1966) has taken place for a certain detergent. Yeasts cells tagged with P-32 were used as food for Daphnia carinata and the filtering rate was measured from the radioactivity of these crustaceans after a certain period of feeding time. Comparison was made between the feeding rate in the medium with and without the detergent and they appeared to be different.

Food composition of Abramis brama was studied in the shallow, meso-eutrophic Hamry reservoir (Czech Republic). Fish were sampled during the daytime in the pre-spawning period (April), the post-spawning (June), summer (July) and autumn (October) in 2011. The bream sampled comprised two main size groups: small (124-186 mm) and large (210-315 mm) standard length. Twenty specimens of each size group (except April - 40 large fish) were taken for analysis on each sampling occasion. Food composition was evaluated using gravimetric methods. Over the whole season, detritus and aquatic vegetation were the dominant dietary items taken. During summer, the diet of large bream comprised mainly aquatic vegetation. Benthic macroinvertebrates and zooplankton formed a minor part of bream diet over the whole season. Specific food habits of bream could be explained by specific conditions within the reservoir and available food resources.

Grazing potential (GP, in % day&minus;1) was estimated for the plankton communities of 13 Greek lakes covering the trophic spectrum, in order to examine its sensitiveness in discriminating different classes of ecological water quality. Lakes with high GP values exhibited high zooplankton biomass dominated by large cladocerans or/and calanoids while lakes with low GP values had increased phytoplankton biomass and/or domination of small-bodied zooplankton indicating intensive fish predation. GP successfully distinguished among ecological water quality classes (estimated using the phytoplankton water quality index PhyCoI) indicating its potential use as a metric for ecological water quality assessment. As a next step, PhyCoI index was modified to include GP as a metric in order to enhance the phytoplankton-based ecological status classification of lakes incorporating zooplankton as a supporting factor. The PhyCoI<inf>GP</inf> successfully assessed the ecological water quality in accordance with PhyCoI classification whereas it was significantly correlated with the eutrophication proxy TSI<inf>SD</inf> based on Secchi Depth. Thus, we propose to use the modified phytoplankton index PhyCoI<inf>GP</inf> for monitoring the ecological water quality of lakes.

Calcium (Ca) is an important driver of community structure in freshwaters. We examined the combined effects of increased temperatures and variations in food quantity on the tolerance to low Ca of Daphnia pulex. The aim was to predict the impact of climate warming on this keystone zooplanktonic species in cold-climate lakes. We conducted a factorial life-history experiment in a clone of North American Daphnia cf. pulex to analyse the interaction effects of a temperature increase (17.5 degrees C-21 degrees C) within their physiological preferred range and expected by climate warming over the next few decades and a narrow Ca gradient (0.25-1.74 mg Ca L-1) under stressful vs. abundant food conditions. We found a striking positive synergistic effect of Ca and temperature on D. pulex reproduction at high food conditions. Although the increase in temperature to 21 degrees C greatly reduced survival, high energy allocation to reproduction at high food levels allowed the population to succeed in poor Ca (<0.25 mg Ca L-1). Results suggest that climate warming and higher food availability will make the populations of many cold and Ca-limited lakes more tolerant to low Ca levels with higher growth population rates, thereby altering zooplanktonic community structures and inducing potential cascading effects on the food web. | Organismo Autonomo de Parques Nacionales (Ministerio para la Transicion Ecologica y el Reto Demografico, Spain) PN2017-2403S | Junta de Andalucia RNM-125

Calcium (Ca) is an important driver of community structure in freshwaters. We examined the combined effects of increased temperatures and variations in food quantity on the tolerance to low Ca of Daphnia pulex. The aim was to predict the impact of climate warming on this keystone zooplanktonic species in cold-climate lakes. We conducted a factorial life-history experiment in a clone of North American Daphnia cf. pulex to analyse the interaction effects of a temperature increase (17.5 &deg:C&ndash:21 &deg:C) within their physiological preferred range and expected by climate warming over the next few decades and a narrow Ca gradient (0.25&ndash:1.74 mg Ca L&minus:1) under stressful vs. abundant food conditions. We found a striking positive synergistic effect of Ca and temperature on D. pulex reproduction at high food conditions. Although the increase in temperature to 21 &deg:C greatly reduced survival, high energy allocation to reproduction at high food levels allowed the population to succeed in poor Ca (&lt:0.25 mg Ca L&minus:1). Results suggest that climate warming and higher food availability will make the populations of many cold and Ca-limited lakes more tolerant to low Ca levels with higher growth population rates, thereby altering zooplanktonic community structures and inducing potential cascading effects on the food web.

Calcium (Ca) is an important driver of community structure in freshwaters. We examined the combined effects of increased temperatures and variations in food quantity on the tolerance to low Ca of <i>Daphnia pulex</i>. The aim was to predict the impact of climate warming on this keystone zooplanktonic species in cold-climate lakes. We conducted a factorial life-history experiment in a clone of North American <i>Daphnia</i> cf. <i>pulex</i> to analyse the interaction effects of a temperature increase (17.5 °C–21 °C) within their physiological preferred range and expected by climate warming over the next few decades and a narrow Ca gradient (0.25–1.74 mg Ca L⁻¹) under stressful vs. abundant food conditions. We found a striking positive synergistic effect of Ca and temperature on <i>D. pulex</i> reproduction at high food conditions. Although the increase in temperature to 21 °C greatly reduced survival, high energy allocation to reproduction at high food levels allowed the population to succeed in poor Ca (<0.25 mg Ca L⁻¹). Results suggest that climate warming and higher food availability will make the populations of many cold and Ca-limited lakes more tolerant to low Ca levels with higher growth population rates, thereby altering zooplanktonic community structures and inducing potential cascading effects on the food web.