Trophic structure and biomass distribution on two East Cape rocky shores

Abstract

The distribution and biomass of macrofauna and macroalgae is described for two intertidal rocky shores near Port Elizabeth. The sheltered shore supported more macrofauna species (67) than the exposed shore (61), mainly owing to greater habitat heterogeneity; of 88 species recorded, 40 (46%) were shared. The shores had 13 and 23 macroalgal species respectively, with 9 shared. Ash-free dry biomass averaged 26 g m^-2 over 200 m on the sheltered shore and 56 g m^-2 over 80 m on the exposed shore for macrofauna and 81 g m^-2 and 77 g m^-2 for the algae. Lower animal biomass values on the sheltered shore may partly have been due to exploitation. Macrobenthic biomass was partitioned as follows on the sheltered and exposed shores respectively: grazers 86% and 82%, filter feeders 8% and 13%, carnivores 4% and 5% and deposit feeders 2% and 0%. Species warranting further study are listed.