Influence of sublethal long-term UV irradiation on body mass, reproductionand behaviour of north European Actinia equina

Two strains of 6-8-y old Actinia equina (Anthozoa: Actiniaria) asexually de rived from two individuals collected on the coast of Brittany were artifici ally UV irradiated in long-term experiments in the laboratory. After the an imals had been allowed to adjust to the test aquaria for 15 months, a progr amme of UV irradiation and multiparameter analysis continued for 24 months. Ultraviolet irradiated sea anemones obtained in addition a quasi-solar UV irradiation at intensities representing the daily and annual cycles. Of the three modes of UV irradiation tested, (1X, 2X and 4X), the one with the lo west intensity and duration (1X) corresponded approximately to the irradiat ion to which sea anemones are exposed in their natural habitat in the tidal zone of the southern North Sea. In all three modes all the actinians showe d a similar, highly significant quasi-exponential cl;eight loss immediately after the onset of UV irradiation. The more the animals were irradiated, t he later juveniles were released from the gastrovascular cavity. At 2X the number of active animals gradually decreased after 18 months, whereas with the 4X irradiation mode the amount of activity fell abruptly and significan tly after only eight months and remained at a very low level. Detachment fi om the substrate was also induced by UV irradiation. The experiments showe d genotype-specific differences in body mass and migration. The crucial fin dings were that A. equina individuals that had adjusted Co the laboratory f ar a long time did give clear responses to UV doses and intensities corresp onding approximately to the irradiation in their natural intertidal environ ment or by radiation increased severalfold. The: responses were immediate a nd sometimes irreversible to UV even in naturally occurring intensities and doses. The genotype specificity of some responses provides evidence that t he stressor UV could induce generic modifications of the population.