Development of a subtidal epifaunal community at the island of Helgoland

Abstract

Epifaunal community development on plexiglas panels submerged in Helgoland Harbour (North Sea) was observed over one year. The course of colonization is described, and some data are presented on autecology, reporduction, and growth rate of particular species. About three months after initial settlement, conditions of coexistence in a mixed barnacle-ascidian community began to change increasingly due to heavy competition for space. The colonial speciesBotryllus schlosseri proved to be potentially dominant. Shortly before it attained monopolization by replacing barnacles (mainlyElminius modestus), a major physical disturbance eliminated the fast growing ascidian. The roles of physical factors, of biological interactions, and of historical events in community development are discussed in context with succession theory and other concepts evolved more recently. It is concluded that succession-like processes can occur in subtidal fouling communities, but there the existence of a globally stable climax is unlikely. Generally the concept of multistable points seems to be better applicable to marine ecosystems than that of succession in the classical sense. There is considerable need for further natural history observations and experiments as an empirical basis for current theory and modelling.