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Rotifers display r‐strategy life‐histories and are adaptable to environmental disturbances. Although rotifers constitute a large proportion of zooplankton in river‐floodplain systems, the influence of hydrology on their assemblage has been poorly studied. We postulated that rotifer assemblage and grazing activities were controlled by mechanisms associated with hydrological conditions. We conducted a 5‐year study (Kopački Rit Nature Park, NE Croatia) to assess the influence of hydrology on (a) rotifer assemblage during different hydrological phases, (b) the vertical distribution of rotifer abundance, functional feeding guilds, and grazing intensity, and (c) the main drivers affecting rotifer assemblage in the floodplain lake. The results indicated that (a) during isolation, longer residence time and high phytoplankton biomass microfilter‐feeders (mIff) and macrofilter‐feeders (mAff) grazing rates were similar whereas predators (Pr) were the most efficient consumers, (b) during high flow pulses, high conductivity and variable water level governed rotifer grazing rates of mIff and mAff at a retion of 1:2 and a decline of Pr grazing activity, and (c) during the flood pulse, reduced phytoplankton biomasss still resulted in mAff and Pr domination of the community whereas mIff grazing activity remained at the same level. Under stable hydrological conditions algivorous species codominated with bacterivores and predators, suggesting an increased biodiversity and food web interactions. In contrast, throughout the inundation period, algivorous species predominated. However, differences in rotifer assemblage between normal flow and flood pulses indicated the importance of hydrology in shaping rotifer trophic structure through modifying lower trophic levels and the availability of food sources.

To estimate the impacts of an Al-contaminated aquatic environment on DNA integrity in the blood cells of eastern mosquitofish Gambusia holbrooki Girard 1859 inhabiting Lake Njivice (Island of Krk, Croatia), an evaluation using the alkaline comet assay was carried out. Genome integrity was studied in parallel with the same fish species inhabiting the nearby, unpolluted Lake Ponikve. The amount of DNA damage in cells was estimated from three different parameters: comet tail length as the extent of genetic material migration, tail intensity (% DNA in the comet tail) and tail moment. The results indicate the loss of genome integrity in blood cells of mosquitofish inhabiting Lake Njivice and the genotoxicity of this aquatic environment. Using the same assay, acute genotoxicity of contaminated water and sediment was evaluated and confirmed on fish, mouse and human blood cells treated ex vivo. Results of the present study indicate that the alkaline comet assay applied to fish blood cells is a valuable tool for determining the potential genotoxicity of water pollutants and confirm its usefulness in the evaluation of DNA damage in fish living in Al-polluted waters.

In this pilot study, we evaluated the usefulness of the alkaline comet assay as a biomonitoring tool at the level of plankton communities affected by varying water quality. Zooplankton was collected in autumn 2007 and spring 2008 in two shallow lakes, one being predominantly polluted with aluminium compounds as result of water treatment process (Lake Njivice; 45°10′ N, 14°30′ E) and the other unpolluted (Lake Ponikve; 45°05′ N, 14°30′ E) used as control. Water and sediment chemistry parameters were assessed at both lake sampling sites. The results indicated that the main pollutant in both matrices was aluminium, whose concentrations exceeded the value of 0.15 mg/L −1 legally accepted for drinking water by Croatian water quality regulations. Plankton composition of the investigated lakes showed that only a few species are dominant and appear at both sites. Cladocerans are represented by Daphnia magna Straus 1820, and copepods by the calanoid Eudiaptomus padanus etruscus (Losito 1901), the cyclopoid Cyclops sp. and dipterans by larvae of Chaoborus flavicans (Meigen 1830). Other species were determined only occasionally and with low abundance. As observed, the comet assay had adequate sensitivity to detect the differences in levels of DNA damage among the dominant zooplankton taxa. Zooplanktons collected in Lake Njivice show a lower degree of DNA integrity compared with animals from the reference lake (Lake Ponikve). Inter-species variability in DNA damage was observed, indicating different genome susceptibility to the same genotoxic pollutants present in the aquatic environment. Furthermore, in the polluted Lake Njivice, seasonal differences in the levels of DNA damage within particular species of zooplankton were also noted. Calanoida, Daphnia and Chaoborus mainly had higher values of all three comet parameters in autumn 2007 than in spring 2008. Feeding modes strongly influenced the level of DNA damage in zooplankton species studied. We assume that the mechanisms of DNA damage and genotoxicity, as Water Air Soil Pollut (