EFFECTS OF THE WATER LEVEL FLUCTUATION ON THE LITTORAL INVERTEBRATE COMMUNITIES IN LAKE BALATON, HUNGARY

László G.-Tóth, Balaton Limnological Institute, / Szent István University, Hungary
Csilla Balogh, Balaton Limnological Institute, Hungary
Laura Parpala, Institute of Biology of the Romanian Academy, Bucharest, Romania
Ilona B.-Muskó, Balaton Limnological Institute, Hungary

Abstract

During the long-lasting drought between 2000 and 2003 in Hungary, water level of the shallow Lake Balaton (mean depth is 3.25 m) the decreased with one meter. By the end of 2003 the sublittoral habitats became dried in 90%, and enormous mass of the aggregates of the settled mollusc Dreissena polymorpha and other invertebrates inhabiting the sublittoral perished. Similar shrinkage phenomenon is in progress from 2011 in Lake Balaton. We developed a model for estimation of the current underwater littoral surfaces available for benthic invertebrates at different water levels based on GIS observations. The model was tested at different water levels by in situ sampling of the different available underwater surfaces (stones, concrete walls, wooden piles, reed fibers etc.) and of the abundance of the invertebrate community inhabiting those. Additional experiments were performed on the tolerance of the aquatic invertebrates against changes of the ionic concentration, temperature, humidity and of the dehydration. We concluded that among several abiotic and biotic factors water level fluctuation is deterministic for the formation of the structure and abundance of the littoral invertebrate fauna in Lake Balaton.