Temporal and Spatial Variations in Exploited and Non- Exploited Populations of the Intertidal Limpet Cellana Capensis

Temporal and spatial variations in the density, size compostion and growth of exploited and non-exdploited populations of the intertidal limpet Cellana capensis from the Transkei coast of southern Africa, between 1989 and 1991, are described. The timing and intensity of recruitment varied between shores and amongst sites within shores. Recruitment success was relatively poor and, in fact, at some of the protected sites no recruitment was recorded until July 1991. Juvenile and adult limpets were both significantly more abundant at the exploited than at the protected sites. The gradual decline in density of limpets observed at the latter sites reflected poor recruitament as well as senescence of older individuals. The extent of variations in density amongst shores was also found to vary from censius to census. Limpets at the exploited sites tended to be much smaller than those found at the protected sites. Although there were initially no differences in the size of limpets amongst sites withing shores marked differences became apparent during the course of the study. This finding, together with the observation of marked annual differences in population size compostion at several of the study sites highlighted the temporal instability of these populations. Such results have profound implications for comparative studies of population size composition. The absence of significant differences in growth rate amongst shores suggests that differences in the intensity of competitive interactions may have been offset by the higher microalgal production at the exploited shore. It is also suggested that upshore migration of largter individuals may counter the intense competition experienced at mid-tidal levels on the exploited shore. Differences in the rate of recritment could also account for some of the observed differences in population characteristics. Both of these explanations are viable alternatives to an earlier proposal which attributed differences solely to the effects of size-selective predation by man.