Collapse of the Crustacean Mesozooplankton in the Northern East China Sea: Effects of the Three Gorges Dam?

Abstract

The damming of major rivers can have broad impacts on ecological processes in adjacent marine ecosystems. Thirty years of sampling data from the northern East China Sea show that the recent impounding of water by the Three Gorges Dam on the Changjiang River (Yangtze River) might have had dramatic impacts on the mesozooplankton community. The reduction in freshwater discharge and subsequent increases in phytoplankton biomass have resulted in a substantial increase in total mesozooplankton wet weight but sharp declines in the abundance of all of the crustacean components. The increase in mesozooplankton biomass is probably associated with an increase in small, gelatinous zooplankton. Together with an increase in sea surface temperature in the region, the reduced freshwater and sediment discharge might have led to the proliferation of gelatinous mesozooplankton in this historically overfished region, generating significantly increased grazing pressure on planktonic crustaceans.