Ultraviolet radiation and distribution of the solitary ascidian Corella inflata (Huntsman)

The solitary ascidian Corella inflata is a common fouling organism in many areas of Puget Sound and the San Juan Archipelago, Washington, USA. Despite its abundance, it is conspicuously absent from areas that receive direct s unlight. Previous work suggests that ascidians in unshaded habitats can be overgrown and killed by algal overgrowth. In this study, we tested the hypo thesis that UV irradiation contributes to C inflata distribution by killing individuals exposed to direct sunlight. To test this, we exposed C. inflat a embryos, larvae, juveniles, and adults to UV irradiation and measured the responses. We also tested for UV-absorbing compounds in larvae, juveniles, and adults. In the laboratory, UV significantly damaged all life stages; t he earliest stages were most vulnerable. A 3-week UV exposure significantly shortened adult life span. Juveniles suffered 100% mortality after only 3 days. Tadpole larvae decreased settlement and metamorphosis after 1 day of UV exposure, and embryos exhibited developmental abnormalities after only 3 0 minutes of exposure. None of the life-history stages had apparent UV-abso rbing compounds. Given the vulnerability of this species to UV, we suggest that its unique life-history traits (i.e., time of spawning, brooding behav ior, length of larval life) help it persist in its preferred habitat and av oid dispersal into inappropriate, UV-exposed areas.