Community-level analyses of long-term changes in rocky littoral fauna from South Africa

Changes in the structure of benthic invertebrate communities in undisturbed and experimentally cleared quadrats on 3 rocky shores on the east coast of South Africa were monitored quarterly for 14 yr from 1982. There were no clear long-term trends in species diversity in either undisturbed or experimentally cleared areas. Diversity decreased and became more variable following disturbance and remained so throughout the study. Fourier analyses revealed significant annual cycles in diversity in undisturbed areas at all sites, while only half of the cleared areas exhibited significant annual cycles. Non-metric multidimensional scaling ordinations, based on Bray-Curtis similarity matrices, were used to represent, traces of the 'state' of the community through time at each site. Undisturbed areas typically exhibited 2 or more apparently stable states, persisting for periods exceeding the turnover time of the dominant populations, with brief periods of instability between them. Fluctuations in the abundance of barnacles and periwinkles accounted for most of the differences between these states. The lower balanoid zone community tended to oscillate between states more frequently than that in the upper balanoid zone. Correlations between traces from different sites tended to be stronger for high shore communities than for those lower on the shore. Disturbed communities either converged to a stable state, persisting for more than 10 yr, or remained unstable throughout the study. Similarities in long-term variability between sites suggest the influence of large-scale factors affecting the supply and survival of larvae.