Simplification of macrozoobenthic assemblages related to anthropogenic eutrophication and cyanobacterial blooms in two large shallow subtropical lakes in China

Eutrophication has become a serious problem in lakes in the middle and lower reaches of the Yangtze River, and is exerting profound pressures on the aquatic communities. However, little research has been conducted on the effects of eutrophication on benthic communities in these lakes. In this study, we investigated macrozoobenthic assemblages in two large shallow lakes (Lake Chaohu and Meiliang Bay in Lake Taihu), which have each experienced severe environmental deterioration and increased occurrences of cyanobacterial blooms in the past few decades. To analyze the changes in benthic community structure over the long-term, we compared the present community with communities from previous studies. Our results showed that present benthic assemblages have simplified substantially compared to communities in the past. In Meiliang Bay, Tubificidae and Chironomidae exclusively dominated the benthic community in 2007, in contrast with the relatively high diversity of benthic community in 1994, with several taxa sharing dominance of the community. Similarly, benthic assemblages in Lake Chaohu changed greatly over two decades, shifting from dominance by Bivalvia in 1980-1981 to dominance by Tubificidae and Chironomidae in 2008-2009. These observed changes in benthic assemblages are discussed relative to the ability of individual different taxa to tolerate eutrophication, algal blooms, Microcystins and associated habitat deterioration.