TEMPORAL VARIATION IN FORAGING BEHAVIOR OF PATELLA-GRANULARIS (PATELLOGASTROPODA) AND SIPHONARIA-CONCINNA (BASOMMATOPHORA) ON A SOUTH-AFRICAN SHORE

Foraging activity of two mid- to low- shore species of limpet, Patella granularis (Prosobranchia) and Siphonaria concinna (Pulmonata) from a n exposed shore on the Eastern Cape coast of South Africa was monitore d. In both species, activity was compared during spring and neap tides and, in P. granularis between summer and winter. Rhythms of activity of the two species were similar, with foraging excursions being mainly associated with nocturnal low tide times, although some P. granularis foraged during daytime low tides. It is suggested that foraging excur sions in P. granularis are triggered by wave action. Both species fora ged further on spring tides than on neap tides and this is suggested t o be a result of the limited time limpets have to forage. P. granulari s was also found to forage further during summer when compared to wint er and the possibility that seasonal micro-algal productivity influenc es foraging distances in limpets is discussed. The foraging activity o f both species could be divided into 3 distinct phases, a relatively r apid outward phase, a much slower foraging phase and a rapid homeward phase. Whether or not these limpets graze throughout an excursion is n ot known. S. concinna was found to home to a fixed scar, although duri ng the experiment some scar-swapping occurred. P. granularis did not h ome to a fixed scar but possessed a 'home range' (approx. 5 cm(2)) to which it returned after each excursion. Patella granularis was found t o move randomly during foraging, whilst S. concinna foraged in a nonra ndom direction which took individuals upshore. No tidal-influence is t hought to be present in this case and the possibility of a learning co mponent in the foraging behaviour of certain limpet species in relatio n to the return to optimal feeding patches is discussed.