The role of colonial ascidians in altering biodiversity in marine fouling communities

Abstract

A suite of invasive species, each with their own unique morphologies, have recently becomemembers of Gulf of Maine, ME USA subtidal communities (Harris and Tyrrell, 2001; Pederson et al., 2005). Three of these species, Botrylloides violaceus, Diplosoma listerianum and Didemnum sp., are colonial ascidians and have become major space occupants in New England fouling communities (Berman et al., 1992; Osman and Whitlatch, 1995, 1999; Whitlatch et al., 1995; Bullard et al., 2007-this issue). They are warm water, two-dimensional species that dominate during seasons of greatest fouling species recruitment (Stachowicz et al., 2002). Therefore, the presence of these species in the Gulf of Maine may significantly influence the recruitment of other species to fouling communities. The goal of this study was to examine the role of the three colonial ascidians in the development of fouling communities by comparing the recruitment of species onto panels containing organisms with different functional morphologies. We conducted field studies at two sites with similar species composition in Portsmouth Harbor, Newcastle, New Hampshire, USA. The communities occupying the floating docks at these sites included blue mussels (Mytilus edulis), the sea anemone Mitridium senile, encrusting