Patterns and processes of benthic biological communities on the intertidal rocky shores of Unguja Island, Tanzania

Understanding biological patterns within ecosystems, as well as the role of key ecological processes governing such patterns is an important ecological and management undertaking. In this study, descriptive and manipulative approaches were used to assess patterns and ecological processes within the benthic communities of the intertidal rocky shores on Unguja Island. Precisely, this study sought to: describe macro-benthic composition and their patterns of distribution; determine the spatial patterns of macrofauna associated with major algal communities (Ulva, Gracilaria, Chondrophycus, Halimeda and Turbinaria); describe spatio-temporal patterns in the abundance of epilithic microphytobenthos; determine the effect of small scale topographic heterogeneity on colonization of intertidal rocky shores by benthic macro fauna. General community analysis was undertaken by digital photography. Chlorophyll-a proxy was used to assess the spatio-temporal trends in abundances of epilithic microphytobenthos. Artificial substrates were used to simulate the effect of small scale topographic heterogeneity on macrofauna colonization. No significant spatial variations in macrobenthic abundances were found among the rocky shores of Unguja Island. However, differences in species diversity as well as assemblage structures were recorded. Both the abundance and diversity of macro fauna varied significantly among the major macroalgal communities. Increased levels of topographic heterogeneity were shown to affect the settlement and recruitment of benthic macro fauna. Besides, taxa-specific preferences to topographic heterogeneity sets were noticed. The Results of the present study demonstrate high level of micro and macrobenthic abundances and diversity on the intertidal rocky shores of the Island of Unguja. Besides, the role of important ecological processes governing the establishment of macrobenthic communities was demonstrated. This study provided the first opportunity to understand spatial and temporal dynamics within the tropical rocky shores of Unguja Island, generating vital baseline information on patterns of biological assemblages. This information will be useful in guiding decisions for the proper management of the intertidal resources and the marine ecosystems in general.