THE IMPACT OF SHORT-TERM EXPOSURE TO UV-B RADIATION ON ZOOPLANKTON COMMUNITIES IN NORTH TEMPERATE LAKES

We exposed natural zooplankton communities to in situ levels of sunlig ht for 3 days at different depths in two north temperate lakes: one ol igotrophic and one eutrophic. Natural fluxes of UV-B radiation (280-32 0 nm) were manipulated with cutoff filters (Mylar(R)). There was subst antial mortality in some of the zooplankton exposed to UV-B in the oli gotrophic lake, but not in the eutrophic lake. Reproduction of Diaptom us was suppressed by UV-B down to 6 m in the oligotrophic lake. These data suggest that natural levels of UV-B radiation in the oligotrophic lake may prevent some species of zooplankton from continuously exploi ting the warm surface waters during summer stratification. In the more eutrophic lake, UV-B is a less important constraint in the vertical d istribution of zooplankton. These differences in the responses of zoop lankton to natural UV-B radiation in lakes may alter their ecological interactions with food resources, predators and other environmental va riables in the water column.