Biogeographic patterns in rocky intertidal communities in KwaZulu-Natal, South Africa

Abstract

On the east coast of southern Africa, marine biogeographic boundaries have previously been unresolved. This paper analyses large-scale patterns of community structure of rocky intertidal shores along the whole of the KwaZulu-Natal coast, based on abundance data covering 220 macroalgal and invertebrate species at 39 sites and using hierarchical cluster analyses and multidimensional scaling to define biogeographic regions. ANOSIM showed that rocky shores in the northernmost region, termed Maputaland, were significantly different from those in three other regions to the south, which fall within a single biogeographic region termed the Natal Province. A clear biogeographic break between these two provinces was identified at Cape Vidal Point, with >65% Bray Curtis dissimilarity in community structure between Maputaland and Natal. This break was detectable in both the low and mid shore, but in the high and top shore, communities converged and there was no regional differentiation for these zones. There was no evidence of a previously suggested biogeographic break near Durban. The major species distinguishing Maputaland and Natal were identified using SIMPER analyses and correspond with previously described differences between Moçambique and KwaZulu-Natal. Species characteristic of Maputaland have tropical affinities and it is proposed that this region forms part of the tropical Indo-West Pacific Province. Natal appears sufficiently distinctive to be recognised as a subtropical biogeographic province different from Maputaland, and possibly different from the warm-temperate South Coast Agulhas Province. The virtual absence of representative unexploited shores in the Natal Province and the occurrence of subsistence harvesting on almost all rocky shores in Maputaland (including those in theoretically protected areas), constitute obvious gaps in the biodiversity conservation strategy of KwaZulu-Natal.