Utjecaj emerzne vegetacije na sastav zooplanktona i epifitona u rukavcima rijeke Krapine

The research of zooplankton and epiphyton was conducted in the summer of 2008 in two oxbow lakes of the river Krapina. The investigation included rotifers (Rotifera), cladocerans (Cladocera) and copepods (Copepoda). Zooplankton samples were collected in free-water zone and littoral of each lake. Epiphyton samples were scraped from plants surfaces (Iris pseudacorus and Mentha aquatica) taken at the littoral stations. The following hypotheses were set: (i) width of littoral zone and water clarity affect horizontal distribution of zooplankton in shallow lakes; (ii) width of macrophyte bed and plant stem structure affect epiphyton composition. The research goals were: 1) to analyse qualitative and quantitative differences of zooplankton composition both in free-water and in littoral zone of lakes with different water clarity; 2) to analyse effects of environmental and biotic factors on both free-water and littoral zooplankton composition; 3) to determine effects of environmental and biotic factors on both the qualitative and quantitative epiphyton composition. Environmental factors and food resources did not differ significantly within the lakes. However, between the lakes the significant difference in water clarity and chlorophyl a was determined. RK1 smaller water clarity was induced by a narrower macrophyte bed and a greater concentration of suspended organic matter, while RK2 greater water clarity was induced by a wider macrophyte bed zooplankton composition. In zooplankton composition of both lakes dominant Rotifera were species of genus Polyarthra and species Keratella cochlearis and Copepoda larval stages. Cladocera were represented with smaller species in RK1, while in RK2 larger species were found. Algivoric Rotofera and Copepoda were dominant in free-water zones because of food availability. Fish predatory pressure was reduced by smaller water clarity and higher trophy state in RK1. Abundance of Bosmina longirostris in free-water was determined by food competition with K. Cochlearis and by water clarity, i.e. fish predation which was particurlary visible in RK2 due to a greater water clarity. The higher water clarity indicates lesser trophy level of RK2 in relation to RK1, which was manifested in a smaller zooplankton abundancy. The lake with the wider macrophyte bed had a greater number of epiphyton species. The greater epiphyton abundancy was detected on the morphologicaly more complex stems of Mentha aquatica compared to the simpler ones of Iris pseudacorus. Plant species diversity and wider macrophyte bed intensly affect epiphyton diversity and abundance.