Abstract

The current, growing increase in penetration of ultraviolet (UV) radiation that has been reported over southern South America, would allegedly alter lacustrine ecosystems by bringing about photoprotective responses in biotic elements. The lacustrine zooplankton in the area is characterized by a predominance of calanoid copepods, mainly Boeckella spp., over cladocerans of the genus Daphnia, because the first group presumably has a higher tolerance towards exposure to ultraviolet radiation. An experiment was conducted involving exposure of two species of crustacean zooplankton to natural ultraviolet radiation, and providing protection from it by using two levels of chlorophyll a concentration. This study involved the non-pigmented species, Boeckella gracilipes (Daday, 1902) and Daphnia pulex (De Geer, 1778). The results showed that D. pulex exhibited a low mortality at high chlorophyll a levels, and concurrent protection against UV radiation. In contrast, B. gracilipes showed a significant, low mortality under exposure to UV radiation. © Koninklijke Brill NV, 2005.