SEDIMENT MACROBENTHOS OF MANGROVE FLATS AT INHACA ISLAND, MOZAMBIQUE

The composition of macroinvertebrate communities in the mangroves of I nhaca island, Mozambique, was analysed. Faunistic samples and sediment cores were collected in order to assess relationships between grain-s ize distribution, organic matter, phytopigments and the species distri bution in two different mangroves: Saco and Ponta Rasa. Results showed the dominance of medium and fine sands rather than colloidal sediment ation, which is originated from the island itself. A clear zonation of benthic organisms is a function of several combined environmental fac tors which contribute to define mangrove communities. Here they are cl early dominated by polychaeta, in a similar situation as in the SW Mad agascar mangroves. Grain-size, together with salinity and ground water were found to be the major factors affecting the macrobenthos distrib ution. The Saco mangrove constitutes a southern example of a subtropic al mangrove with high diversity and production. The Ponta Rasa mangrov e may be considered as an atypical one, or an extreme situation to sub tropical mangrove, in which diversity is very low and several key-spec ies are lacking. The differences between these two mangroves suggest t hat microenvironmental conditions, namely water content of sediments a nd phytobenthos, are determinant to the richness and faunal diversity of these ecosystems.