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 content and soil water salinity along the Adelaide River floodplain during the late dry season. Twenty two species of mangrove were identified, four of which have not been recorded previously from the Adelaide system: Acanthus ebracteatus, Avicennia integra, Rhizophora apiculata, and R. lamarkii. Species richness was minimal in areas experiencing prolonged exposure to extremes of either freshwater or hypersaline conditions (regardless of whether those conditions are products of the river salinity regime and/or pronounced seasonal cycles of waterlogging and drying), and maximal in areas where moderate salinities and high soil water contents prevail in the late dry season. Three ecophysiological hypotheses are suggested which might provide mechanistic bases for understanding local variation in species richness along natural salinity gradients.