Document: CRA-3-74-9

UV radiation and zooplankton distribution across vertical habitat gradients in three glacial lakes of differing transparency.

WILLIAMSON, C.E.* and D.M.LEECH

Lehigh University, Bethlehem, PA 18015 ¹

Abstract:
The water column of stratified lakes can be viewed as a habitat gradient in both space and time where variations in temperature, predation, and food availability are well-recognized as important variables influencing the distribution and abundance of zooplankton. To date, little consideration has been given to the role of UV radiation (UVR) in zooplankton communities. We used a 3 year database on three lakes of differing transparency to evaluate the relationship between potential exposure to solar UV and the vertical and seasonal distribution and abundance of several zooplankton species that differed in their UV tolerance. In most years, UV intensity in the surface mixed layer decreased from early stratification in May to late stratification in September, largely due to changes in the depth of the mixed layer. A higher frequency of statistically significant negative relationships between zooplankton abundance and high UV habitats was observed in zooplankton taxa with low UV tolerance than in taxa with high UV tolerance. Cladocerans, which are the least UV tolerant of the three major taxa, tended to avoid the surface waters of the highest UV lake during periods of high UVR, while the much more UV-tolerant copepods and rotifers showed little or no evidence for avoidance of high UV habitats. Within lakes, the relationship between UV avoidance and taxon was evident only in the highest UVR lake. Visual predation is an unlikely alternative explanation because fish stocks and the potential for visual predation are higher in the two lower UV lakes. These data are consistent with the hypothesis that UV radiation influences zooplankton community structure and dynamics in UV-transparent lakes.

Keywords: UV Radiation, Habitat Gradients, Zooplankton Migration

This abstract is being presented at: 10:15 AM in session:
Oral Session #54: Lake Ecology.