Effects of long-term ultraviolet radiation: the white form of Metridium senile (Anthozoa : Actiniaria) as a potential biological indicator for ultraviolet

Genetically identical individuals of the white form of Metridium senile wer e kept in the laboratory for 40 months, during almost 2 years of which they were irradiated with ultraviolet (UV) radiation simulating the shape of th e solar UV spectrum. The living and experimental conditions were largely ma tched to the conditions in the sea anemones' natural habitat on the North S ea coast. Controls were shielded from direct radiation or irradiated with o nly the visible range of the spectrum; for the UV tests, the UV component c orresponded either to the conditions in the natural habitat or to twice or 4 times this dose. All experiments were preceded by a several-month settlin g-in period, and UV irradiation was always begun at a low intensity. Under these conditions UV was not lethal but produced many parameter changes, of which only those that were irreversible for the entire duration of the expe riment, from September 1992 to August 1994, are described here. The body ma ss fell significantly in all three UV-radiation modes. All irradiated anima ls positioned themselves so as to be less exposed to the radiation, and all changed colour from white to brown. These responses are discussed with ref erence to the potential of M. senile as an indicator or monitor for UV in t he northern European coastal region. Field analyses are currently being con ducted to demonstrate the extent to which the present results apply to fiel d conditions.