Lethal effect induced by ultraviolet-B in a planktonic copepod: Role of the post-irradiation time on mortality measurements

The vulnerability to W-B radiation in Acanthocyclops robustus was analyzed in the laboratory. The LD50 for adult individuals, determined by mortality one day after UV-B exposure was 40 mu Wcm(-2) For 4 h exposure. PL signific ant increase in the mortality of A. robustus adults was observed four days after exposure to UV-B irradiation. As a consequence, the estimated lethal dose at four days post-exposure was 20% less than that estimated two days a fter the exposure. These results indicate that because there is significant latent mortality during the post-irradiation period, accurate assessment o f mortality due to UV-B exposure can only be made four days after the irrad iation. Copepodite IV life stage individuals were much more sensitive to UV -B exposure than were the adults.