UV radiation as a potential driving force for zooplankton community structure in Patagonian lakes.

This article explores the potential role of UV radiation (UVR) as an influence on zooplankton communities. In the first section we provide a general overview of UVR effects on freshwater zooplankton, with an emphasis on Argentine and Chilean environments. In the second section we present the results of a survey involving 53 temperate lakes across a gradient of UVR exposure to determine patterns of species richness and specific diversity. These community characteristics decreased at high potential UVR exposure (i.e. high mean water column irradiance or low lake optical density). A threshold value of mean water column irradiance of approximately 10% of the surface level seems to limit both richness and diversity to minimum values. On the basis of the collected evidence it is not possible to definitely conclude that UVR rather than another covarying factor is responsible for the decrease in specific diversity observed at the lowest end of lake optical depth. However, lakes with values above the previous threshold are likely to exhibit highly depauperate zooplankton communities regardless of the mechanism. As a cautionary note we suggest that changes in the optical characteristics (i.e. changes due to atmospheric conditions, precipitation patterns or vertical displacement of the tree line) may result in sudden shifts in zooplankton community structure.