On the biology ofAurelia aurita(L.) 3. Predation byCoryphella verrucosa(gastropoda, opisthobranchia), a major factor regulating the development ofAureliapopulations in the Gullmar Fjord, Western Sweden

This paper describes field and laboratory observations on the relationship between a nudibranch gastropod (Coryphella verrucosa) and the development of populations of the scyphozoan Aurelia aurita. Predation tests showed that C. verrucosa ingests Aurelia polyps at a high rate (up to 200 polyps × d−1) and that this predation, which occurs mainly in October, is the chief factor responsible for the drastic decline in polyp abundance. In turn, it seems that in this area, C. verrucosa is totally dependant on Aurelia as a prey organism. It appears when the polyps begin to develop in August–September, matures in October, and declines in vitality and dies in November. The hypothesis is proposed that predation by C. verrucosa, and the survival of ephyrae during the winter period are the two main factors regulating the size of the Aurelia population the following summer.