MANGROVE SPECIES RICHNESS IN RELATION TO SALINITY AND WATERLOGGING - A CASE-STUDY ALONG THE ADELAIDE RIVER FLOODPLAIN, NORTHERN AUSTRALIA

Mangrove species richness was surveyed in relation to soil water conte nt and soil water salinity along the Adelaide River floodplain during the late dry season. Twenty two species of mangrove were identified, f our of which have not been recorded previously from the Adelaide syste m: Acanthus ebracteatus, Avicennia integra, Rhizophora apiculata, and R. lamarkii. Species richness was minimal in areas experiencing prolon ged exposure to extremes of either freshwater or hypersaline condition s (regardless of whether those conditions are products of the river sa linity regime and/or pronounced seasonal cycles of waterlogging and dr ying). and maximal in areas where moderate salinities and high soil wa ter contents prevail in the late dry season. Three ecophysiological hy potheses are suggested which might provide mechanistic bases for under standing local variation in species richness along natural salinity gr adients.