The importance of zoobenthos in the ecosystems of tropical oxbow lakes

摘要

Tropical lowland and floodplain lakes experience large water level changes according to rain events as well as the alteration of wet and dry seasons. Flooding events govern the nutrient dynamics (MOBERG et al. 2002) and have been gained attention with regard to the maintenance of biodiversity (SEGERS et al. 1993, SHIEL et al. 1998, TEJERINA-GARRO et al. 1998). Previous studies in 2 humic oxbow lakes in peat swamp areas of Borneo have shown that rotifers are dominant in density, and rotiferan species richness is high during high water level periods (GU-MIRI 2002, GUMIRI & IWAKUMA 2002). Although oxbow lakes are shallow in nature, the dissolved oxygen concentration at the bottom layers becomes very low, more so in lakes isolated from the main river than in lakes open to the main river throughout the year (GUMIEI IWAKUMA 2002). Both large water level changes and hydrological connectivity to the main river affect the aquatic communities. Since annual litter fall amounts in this area reach 500 g m~(-2) (RAHAJOE & KOHYAMA 2003), allochthonous litter input as well as dissolved organic carbon may provide a substantial energy source for both benthic and planktonic food chains. We estimated the biomass of zoobenthos in 2 hydrologically different oxbow lakes, to compare the values with zooplankton biomasses, to compare zoobenthos commu-nities and biomasses between shallow sites and deep central sites, to evaluate the impact of lake mixing events on zoobenthos community, and to compare biomasses of zoobenthos and zooplankton.