Abundance and distribution of sessile invertebrates under intertidal boulders (São Paulo, Brazil)

Abstract

The encrusting communities under two boulder fields (Praia Grande and Ponta do Baleeiro) were monitored monthly during 1990 and 1991, in São Sebastião, on the northern coast of São Paulo State, Brazil. Two sizes of boulders were chosen: small (20-30 cm² underside area) and larger ones (160-220 cm²) located on the middle and lower levels of the intertidal. The community's components were mainly sessile animals either compound ones such as Bryozoa, Ascidiacea, Porifera and Cnidaria, in this order of abundance, or simple ones such as Polychaeta and Bivalvia, also in this order of abundance. All groups, except by serpulids (Polychaeta), had higher percent cover in the low intertidal region and under large boulders. Diversity was higher at Ponta do Baleeiro, and in the low intertidal region and on large boulders for both shores.