Temporal variation in foraging behaviour of Patella granularis (Patellogastropoda) and Siphonaria concinna (Basommatophora) on a South African shore

Abstract

Foraging activity of two mid- to low- shore species of limpet, Patella granularis (Prosobranchia) and Siphonaria concinna (Pulmonata) from an exposed shore on the Eastern Cape coast of South Africa was monitored. 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 excursions in P, granularis are triggered by wave action. Both species foraged further on spring tides than on neap tides and this is suggested to be a result of the limited time limpets have to forage. P. granularis was also found to forage further during summer when compared to winter and the possibility that seasonal micro-algal productivity influences foraging distances in limpets is discussed. The foraging activity of both species could be divided into 3 distinct phases, a relatively rapid outward phase, a much slower foraging phase and a rapid homeward phase. Whether or not these limpets graze throughout an excursion is not known. S. concinna was found to home to a fixed scar, although during the experiment some scar-swapping occurred. P. granularis did not home to a fixed scar but possessed a 'home range' (approx. 5 cm2) to which it returned after each excursion. Patella granularis was found to move randomly during foraging, whilst S. concinna foraged in a non-random direction which took individuals upshore. No tidal-influence is thought to be present in this case and the possibility of a learning component in the foraging behaviour of certain limpet species in relation to the return to optimal feeding patches is discussed.