No abstract

Abstract. In the present study, the sensitivity of four coexisting cladoceran species to ultraviolet (UV)-B radiation was evaluated. First, the LD 50 under conditions inhibiting the action of photoenzymatic repair was calculated by exposing cladocerans to different doses of UV-B light only. Animals in another treatment group were exposed to both UV-B and visible light, which allows for photoenzymatic repair. Photoenzymatic repair contributed significantly towards the degree of total tolerance to UV-B light in all groups of cladocerans, although the magnitude of the contribution varied among species. When no photoenzymatic repair was allowed, the most tolerant species was Moina micrura, followed by Daphnia ambigua and Ceriodaphnia dubia, with Diaphanosoma chilense being the most sensitive species. Under conditions permitting the action of photorepair, M. micrura was again the most tolerant species to UV-B light. Ceriodaphnia dubia showed an intermediate tolerance value, whereas D. chilense and D. ambigua were the least tolerant species, with no significant differences between them. Adults and juveniles of C. dubia differed in their sensitivity to UV-B light under conditions with and without photorepair.