This paper presents the results of surveys quantifying species richness of rocky intertidal invertebrates across a potential biogeographic barrier on the south-eastern coast of Australia, as well as at Red Bluff, which is an isolated rock platform within the otherwise soft-sediment barrier. It was predicted that the number and composition of invertebrate species would differ on either side of the barrier and at Red Bluff and that these differences would be related to the potential for dispersal of the constituent species. Time-per-area searches at two sites within each of five rock platforms on either side of the barrier and at Red Bluff revealed that species richness and composition differed significantly on either side of the barrier, and that Red Bluff supported many species on both sides of the barrier, indicating its potential as a stepping-stone. The distribution of species was not related to their potential for dispersal, because potentially ‘good’ dispersers with planktonic larvae were sometimes restricted to one side of the barrier and potentially ‘poor’ dispersers with direct developing juveniles were present on both sides of the barrier. These results support increasing evidence that the geographic distribution of intertidal invertebrates cannot be inferred by simple reference to their life histories.