Ecological effects of introduced sessile marine invertebrates.

Manipulative field experiments were used to investigate the effects of the ascidians Botryllus schlosseri and Ascidiella aspersa and the bryozoan Bugula neritina on sessile invertebrate assemblages. Experiments were conducted on perspex plates suspended from Workshops Jetty, Williamstown, Victoria. All 3 introduced species affected the abundance of sessile marine invertebrates, but the effects were varied and not always negative or concentrated on native species. B. neritina increased the abundance of native species, A. aspersa increased the abundance of introduced species and B. schlosseri decreased the abundance of both native and introduced species. This research shows that effects of some introduced species are highly variable and do not conform to typical ideas that exist for introduced species.