Mangroves and Sediment Dynamics Along the Coasts of Southern Thailand

Mangroves inhabit tropical coastlines and are particularly abundant along deltas and bays where rivers bring freshwater and sediment to the sea. This habitat witnesses great variability in sedimentation and erosion rates, partly governed by variation in hydrodynamics of rivers as well as the sea. Sedimentation and hydrodynamics have a great impact on coastal and mangroves dynamics. Sediment accretion creates new mud flats for colonization whilst exposure to waves and currents may strongly hinder colonization and promote coastal erosion. This study has experimentally quantified responses of mangroves to sedimentation and hydrodynamics. It integrated these findings with demographic and phenological data to develop a simple models and predict mangrove colonization success. Three common Southern Thailand mangrove genera were investigated: Avicennia, Rhizophora and Sonneratia. Responses of the three species were quite different. In sheltered coastal bays, mangroves were able to colonize newly-formed mudflats. Abrupt high sedimentation, however, led to vast mortality in Avicennia but it had less impact on survival and growth of Rhizophora and Sonneratia. Water turbulence had great impact on Rhizophora seedling growth and survival. In contrast, Avicennia and Sonneratia were able to survive and grow well in exposure condition. The integrating models showed that water turbulence and seedling herbivory had the most important impacts on mangrove colonization success. In 30-year simulations, Avicennia was the most successfully colonizing species followed by Sonneratia. Probable sea level rise scenarios seriously reduced colonization success of all species.