SPECIES-SPECIFIC DAPHNIA PHENOTYPES: A HISTORY OF INDUSTRIAL POLLUTION AND PELAGIC ECOSYSTEM RESPONSE

Abstract

Phenotypic differences among species, even closely related species, may translate into distinct effects on ecosystem dynamics. In lakes, the generalist grazer genus Daphnia often has marked effects on the abundance of primary producers, the rate of primary production, and rates of nutrient cycling. The effects are particularly distinct during the clear-water phase (CWP) when algal biomass is driven to extremely low values as Daphnia densities undergo an annual population increase. Here we show that the timing of the CWP in Onondaga Lake, New York, USA, has depended upon which Daphnia species were present in the water column. An analysis of the ephippia and diapausing eggs from the sediments reveals that long-term changes in the zooplankton species assemblage tracks a history of chemical (especially salt waste) pollution. Prior to 1930 the assemblage was dominated by native D. pulicaria and D. ambigua. From 1930 to 1980, these species were replaced by D. exilis and D. curvirostris, two salinity-tolerant ex...