THE ECOLOGY OF TROPICAL SOFT-BOTTOM BENTHIC ECOSYSTEMS

The structure and function of tropical soft-bottom benthic ecosystems are reviewed and compared with seafloor ecosystems of higher latitudes. Diversity of benthic habitats peaks in the tropics. Variations in climate have led to the development of unique sedimentary features and sea-floor habitats such as mangroves, coral reefs, stromatolites, mixed terrigenous-carbonate shelves, fluid mudbanks and hypersaline lagoons. Temporal and spatial patterns of benthos in all latitudes are determined by primary production in the water column and by sediment type and associated physicochemical conditions. In the tropics, however, control of benthic communities is vested in monsoonal rains, high temperatures, hypersaline conditions, carbonate sedimentation and compaction, low and variable oxygen and dissolved nutrient concentrations, chemical defenses by plants, smothering by massive riverine sedimentation, erosion of mudbanks and by anoxia caused by impingement and stratification of water masses. The widest variations in faunal densities and species richness occur in the tropics, coinciding with the great variety of habitats and environmental conditions. Energetically, there is some evidence of higher rates of microbial growth and invertebrate production in the tropics, but pelagic and demersal fish yields to man seem to be equivalent to those in higher latitudes. At the ecosystems level, variations in energy fluxes are as great within a given latitude as they are among latitudes, obfuscating some real differences with latitude. It is clear that the tropics are not a uniform or benign milieu but offer climatic and environmental conditions as inimical to benthic assemblages as the supposedly, more inhospitable, boreal and temperate latitudes.