Abstract

The increase in the penetration of ultraviolet radiation that has been reported lately for freshwater ecosystems in southern South America, would allegedly generate alterations in ecological processes. In the present study, the mortality of Neobosmina chilensis (Daday 1902), a small cladoceran distributed in South American lakes and ponds, was studied in this respect. Specimens were reared in five different concentrations of dissolved organic carbon, and subjected to 24 hrs of exposure to artificial ultraviolet radiation. An inverse correlation between the dissolved organic carbon concentration and individual mortality was found. This result supports the description of a screen effect of dissolved organic carbon against ultraviolet radiation. The data obtained describe a linear relation, in which LC50 corresponded to 4.43 mg/l of dissolved organic carbon. The ecological implications of this result are discussed.