THE INFLUENCE OF RESIDENT ADULTS ON RECRUITMENT - A COMPARISON TO SETTLEMENT

For species recruiting into established sessile communities, the adult colonies and individuals already present form a significant part of t he environment and have the potential to alter both larval settlement rates and post-settlement mortality. Settlement rates can be reduced b y predation on larvae, by the removal or addition of substratum space, or by stimulation or prohibition of larvae from settling on adjacent substratum. Once attached, the recruiting individual can still be infl uenced by predation or overgrowth by residents, by the added physical structure for firmer attachment, or by being camouflaged from motile p redators. To examine those processes by which residents affect recruit ment we exposed experimental substrata with three densities of adults of a single species at a site in eastern Long Island Sound, USA for a 1-wk period. Seven different species of common invertebrates were used in nine separate experiments. The major effect of most resident speci es was the usurpation of space and the restricting of recruitment to a djacent unoccupied areas. This was particularly true for resident asci dians and bryozoans, but less so for barnacles and oysters. In fact se veral species recruited in higher densities on or next to oysters and barnacles. Comparison to 1-day settlement experiments indicated that t he encrusting ascidian species Diplosoma and possibly Botryllus reduce d recruitment relative to settlement, probably by overgrowing newly-se ttled individuals. However, in the presence of most resident species, recruitment patterns were not greatly different from settlement patter ns, indicating that the effects of the attached community on recruitme nt may result from influences on settlement.