Patch Structure in a Tropical Rocky Shore Community in Brazil: A Mosaic of Successional States?

The community of benthic organisms in the lower zone of a rocky shore at Praia Rasa, Brazil is distinctly patchy in structure. We examined the hypothesis that two types of patch (a. red algal turf and b. colonial coelenterate) represent different temporal stages in the same successional trajectory. We made observations on a) the stability of patch boundaries, b) successional sequence in experimental clearings within both patch types and c) species composition through time in undisturbed patches. In most cases, the coelenterate overgrew the algae at the patch boundaries, thus showing a competitive asymmetry. In the successional sequence, diatoms were followed by ulvoid species. Thereafter, within clearings in the algal patches, a red algal turf was once more established over one year. In contrast, the mid successional period in clearings within the coelenterate patch was characterized by very low cover of sessile organisms. Colonization by red algal turfs and by the coelenterate colony is largely dependent on vegetative spread. Thus later succession is not predictable on the basis of time alone. Supply-side processes are clearly of equal importance. Therefore it cannot be stated without qualification that patches of red algal turfs and colonial coelenterate at Praia Rasa are part of the same successional sequence