DYNAMICS OF ROCKY INTERTIDAL COMMUNITIES - ANALYSES OF LONG-TIME SERIES FROM SOUTH-AFRICAN SHORES

The abundance of benthic invertebrates in undisturbed and ex:experimen tally cleared quadrats on three rocky shores on the east coast of Sout h Africa was monitored quarterly for 13 years. Most of the ii commonly occurring species exhibited significant seasonal cycles and, although interannual variability was high, there was evidence of biennial cycl es in abundance. Long-term trends were evident for many species. Limpe ts generally decreased in abundance, while periwinkles and rock oyster s increased. The two numerically dominant barnacles exhibited an inver se relationship over time, and at some sites one species was replaced by the other. There was a high degree of both inter-and intraspecific correlation at small scales, but this was attenuated at scales of tens to hundreds of kilometres. Many of the time series exhibited signific ant discontinuities in which changes in abundance of up to three order s of magnitude were evident. Such discontinuities usually marked the s tart of periods of altered interannual variability lasting for 3-4 yea rs. In some cases, this resulted in time series divided into phases wi th completely different underlying dynamics. After an initial recovery period of up to 3 years, the cleared areas exhibited many of the same characteristics as the controls, but with a tendency for increased in terannual variability. An interesting finding was that areas cleared i n spring and summer did not exhibit the biennial cycles characteristic of undisturbed areas, while those :cleared in autumn and winter retai ned this characteristic. Fluctuations in abundance of intertidal inver tebrates clearly exhibit complex dynamics, which are discussed in term s of possible external forcing functions. (C) 1998 Academic Press Limi ted.