THE EFFECTS OF GIBBULA-CINERARIA (L), NUCELLA-LAPILLUS (L) AND ASTERIAS-RUBENS L ON DEVELOPING EPIFAUNAL ASSEMBLAGES

Recruitment of epifaunal invertebrates was followed on 16 x 16 cm Perspex panels immersed at a low intertidal site at St Andrews, on the east coast of Scotland. Short-term experimental enclosures assessed the importance of grazing by the herbivorous prosobranch Gibbula cineraria (L.), and the nontrophic activities of the predatory species Nucella lapillus (L.) and Asterias rubens L., on developing epifaunal assemblages. At the end of each experimental period, recruits of all seven taxonomic groups examined were less abundant on G. cineraria grazed treatments, than on those from which grazers were excluded. Furthermore, none of the epifauna were apparently able to achieve an escape-in-size during a 2-month period of exclusion of grazers. N. lapillus and A. rubens did not appear to have similar deleterious effects on the developing assemblages (with the possible exceptions of barnacles, hydroids and ascidians during periods of peak larval settlement). Similar numbers of recruits were recorded on the treatment panels and the net controls. Enclosure of N. lapillus appeared to enhance the recruitment of some species (e.g., anomiids). These experiments provide no information regarding the nature of the effects of these consumers on the developing assemblages. However, there is circumstantial evidence that the effects of G. cineraria may be attributable to the rasping-off of recently established recruits, as the snails browse across the substrata.