The invertebrate macrobenthos of artificial rocky shores in the Knysna Estuary

Abstract

Macrobenthic invertebrate communities of artificial rocky shores are described in the Knysna Estuary, South Africa. Eleven vertical transects 0.25 m wide and 1.25-2 m long were sampled. Species richness varied from 10 to 16 species within 297-772 individuals per transect on the rocky shores of the embayment and 13 to 29 species within 1,136-13,153 individuals in the middle estuary. Comparison of communities was made using Shannon-Wiener and Gini-Simpson indices from which the number of 'effective' species was determined within each habitat, and in which the presence of the estuarine mussel, Arcuatula capensis, and its associated polychaet fauna increased biodiversity of the artificial rocky shore in the middle estuary. Indices, correctly determined, were helpful in assessing changes between comparable faunas in dissimilar sites. It is concluded that if civil engineering design took cognisance of the vertical and horizontal parameters controlling the distribution of macrobenthic fauna, particularly with respect to mean sea level, the environmental impact would be significantly reduced.