AN INVESTIGATION OF THE INDIRECT EFFECTS OF INTERTIDAL SHELLFISH COLLECTION

Shellfish collection by humans is a form of selective predation, with the larger individuals of a few target species being taken, and can ha ve direct and indirect effects. We investigated the indirect effects o f collection by experimental removals of two target species, Cellana t ramorerica (Sowerby) and Nerita atramentosa (Reeve) from a rocky shore in south eastern Australia. Removals of single species were compared with the removal of both species and frequent removals were compared a gainst once-off removal events. The removal of Cellana resulted in an increase in micro-algal abundance. This increase was greater where Cel lana were frequently removed than where once-off removal of the specie s occurred. The removal of Cellana also promoted the immigration of ad ult Cellana, but the overall population was dominated by juveniles. Im migration of juvenile Cellana was high in all cases and was not affect ed by removals of either target species. The removal of Nerita, whethe r once-off or frequent, resulted in a decrease in micro-algae, but did not affect the migration of other species. The combined removal of Ce llana and Nerita did not affect microalgal abundance, a result that wa s successfully predicted from the summed effect of the single species removals. In addition, the combined removal had no effect on the abund ance of other species. The single and combined removal of these two ga stropod species did not influence the species richness at this study s ite. (C) 1998 Elsevier Science B.V.