The early development of epifaunal assemblages on artificial substrata at two intertidal sites on an exposed rocky shore in St. Andrews Bay, N.E. Scotland

Abstract

The importance of succession and the seasonality of larval recruitment, on the species composition of epifaunal assemblages which developed on small artificial substrata, was examined. Perspex panels were immersed every month between April 1984 and October 1985, for 5 to 6-month periods, at two intertidal sites on an exposed rocky shore in St. Andrews Bay, north-east Scotland. Recruitment of all species was highly variable, both temporally (varying seasonally and annually) and spatially (varying between sites and different panel replicates). Larvae of the eight taxonomic groups which dominated the developing assemblages, recruited in similar abundances to all the panels immersed at any time, irrespective of the actual date of panel immersion and, consequently, of assemblage age. None of the species consistently recruited in significantly greater (or lesser) numbers onto panels bearing assemblages at specific stages in the developmental sequence, although larvae of all the taxonomic groups generally recruited in lowest abundance onto panels which were immersed for less than 4 weeks. The changing patterns of species composition appeared to be a consequence of seasonal variations in the availability and abundance of larvae potentially capable of settling, rather than a distinct successional sequence.