Macrozoobenthos in Yangtze floodplain lakes: patterns of density, biomass, and production in relation to river connectivity

A systematic investigation of macrozoobenthos was conducted in Yangtze floodplain waters to reveal patterns of density, biomass, and production in relation to river connectivity. In the Yangtze-connected lakes, 78 taxa belonging to 33 families and 62 genera were identified. Macrozoobenthos density was 327 individuals/m(2), biomass was 1.40 g dry mass/m(2), and production was 3.23 g dry mass m(-2) y(-1). The assemblages were characterized by high diversity, high production, and high bivalve-filterer abundance. The key factor determining the macrozoobenthic assemblages was river connectivity. As river connectivity increased, 3 types of response patterns were observed: 1) density, biomass, and production of collector-filterers (mainly Bivalvia), shredders (e.g., Stictochironomus), and predators (e.g., Dytiscidae) showed unimodal changes, i.e., first increased and then decreased; 2) density, biomass, and production of collector-gatherers (mainly Tubificidae and Chironomidae) decreased continuously; and 3) density of scrapers (mainly Gastropoda) decreased, whereas their biomass and production changed unimodally. At an intermediate level of river connectivity, biomass and production of total macrozoobenthos reached maxima, whereas density decreased with increasing river connectivity. Previous research showed that a diversity of zoobenthos also peaks at moderate connectivity with rivers. Therefore, to maintain high productivity as well as high biodiversity in the Yangtze floodplain, protecting the remnants of river-connected lakes and linking disconnected lakes freely with the mainstream are crucial.