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 sunlight. Previous work suggests that ascidians in unshaded habitats can be overgrown and killed by algal overgrowth. In this study, we tested the hypothesis that UV irradiation contributes to C inflata distribution by killing individuals exposed to direct sunlight. To test this, we exposed C. inflata 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; the 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 30 minutes of exposure. None of the life-history stages had apparent UV-absorbing compounds. Given the vulnerability of this species to UV, we suggest that its unique life-history traits (i.e., time of spawning, brooding behavior, length of larval life) help it persist in its preferred habitat and avoid dispersal into inappropriate, UV-exposed areas.