Effects of ultraviolet radiation on the seasonal vertical distribution of zooplankton: a database analysis

Abstract

Recently, small-scale field experiments have demonstrated that exposure to UV radiation can invoke downward migrations in UV-sensitive zooplankton; however, questions remain as to zooplankton responses at the whole-lake scale. Here a three-year database on three lakes of varying UV transparency was used to examine the relationship between UV exposure and the seasonal vertical distribution and abundance of several zooplankton species. We hypothesized that if UV radiation is an important ecological force influencing the vertical distribution and seasonal abundance of zooplankton, the strength of a given species' response to UV would be inversely proportional to its UV tolerance. UV habitat did have a significant effect on zooplankton distribution in taxa with low UV tolerance compared to taxa with high UV tolerance. Cladocerans, which are the least UV-tolerant of three major groups, tended to avoid the surface waters of the highest UV lake during periods of high UV. More UV-tolerant groups, rotifers and copepods, showed little or no evidence for avoidance of high UV habitats. Among lakes, the relationship between UV avoidance and taxon was evident only in the highest UV lake. These data are consistent with the hypothesis that UV influences zooplankton community dynamics in low DOC, UV-transparent lakes.