SOURCES OF NUTRITION IN INTERTIDAL SEA-ANEMONES FROM THE SOUTH-WESTERN CAPE, SOUTH-AFRICA

Respiration rates of seven species of intertidal sea anemones from the south-western Cape, South Africa were measured with and without illum ination to determine whether zooxanthellae contributed to their nutrit ional needs. Light had no significant effect on oxygen exchange in any of the species, suggesting that all are azooxanthellate. Diets of ane mones from two sites, Wooley's Pool in False Bay and Blouberg on the A tlantic coast some 20 km north of Cape Town, were examined by gut cont ent analysis, Seven species occurred at Wooley's Pool, but only one (B unodactis reynaudi) at Blouberg. At Wooley's Pool 39.4% of anemones co ntained food, while at Blouberg only 7.4% did so. A wide spectrum of p rey taxa were consumed by the various anemone species, although consid erable dietary overlap occurred. Pelecypods, gastropods and isopods we re ingested by all the species examined, Pelecypods dominated the diet of B. reynaudi at Blouberg (91% occurrence), but were recorded in onl y 42% of the same species at Wooleyl's Pool. The frequency of occurren ce of pelecypods in the guts of the other species ranged from 9% (Anth othoe stimpson) to 28% (Actinia equina). Gastropods were the main prey items eaten by Anthopleura michaelseni (67% occurrence), Pseudactinia flagellifera (43%) and Pseudactinia varia (42%), while isopods were t he most frequently occurring constituent in the diets of A. stimpsoni (62%) and Bunodosoma capensis (16%). A. equina was the only species fo r which insects were a regular part of the diet (26% occurrence). Plat yhelminths were found only in the guts of B, capensis (11%); holothuri ans only in B. reynaudi at Wooley's Pool (2%), and crinoids only in P. flagellifera (2%). Large quantities of algal material and indigestibl e debris were also ingested, indicating that sea anemones are non-sele ctive feeders. Cluster analysis and multi-dimensional scaling techniqu es revealed four distinct feeding groups among the anemone assemblages , These are characterized as microphagous (A. stimpson), generalist (B , capensis and A. equina), macrophagous (B. reynaudi at Wooley's Pool, A. michaelseni, P. flagellifera and P, varia) and specialist bivalve- feeder (B. reynaudi at Blouberg).