Effects of zooplankton on the sinking flux of organic carbon in Lake Biwa

Abstract

To clarify the roles of zooplankton in the sedimentation of seston from the epilimnion, the sinking flux of particulate carbon was measured along with primary production rate and zooplankton biomass from July 1996 to October 1997 at a pelagic site in the north basin of Lake Biwa. During the study period, the flux varied seasonally from 66 to 510 mg C m−2 day−1 and was low in summer when zooplankton, composed mainly of Eodiaptomus japonicus and Daphnia galeata, were abundant. Simple correlation analysis revealed that the sinking flux correlated neither with the primary production rate nor with the amount of sestonic carbon above the sediment trap. However, the particle elimination rate, estimated as the difference between the primary production rate and the sinking flux, correlated positively with the zooplankton biomass. These results suggest that zooplankton play a substantial role in decreasing the sinking flux in Lake Biwa.