Mangrove Swamps: Causes of Decline and Mortality

Mangroves occur in coastal settings of estuaries, deltas, lagoons, open coast, carbonate islands, and rare inland situations, and through high productivity there sustain significant food-chains. Forest decline and mortality of mangroves has been documented to be caused by natural disturbance, direct human induced changes to the mangrove habitat, and sea level rise. Significant areas of mangroves have been converted by coastal development in the last two decades in particular, and better understanding of factors causing forest decline and mortality will help conserve remaining areas. Natural disturbance causing massive mortality has included physical damage from storms, sometimes combined with excess sedimentation, and prolonged inundation. Human disturbance causes of mangrove mortality have included excess sedimentation, changes to mangrove hydrological regime, and sea-level rise vulnerability is projected. If sedimentation rates under mangroves do not keep up with rates of sea-level rise rates, stratigraphic records indicate that the mangroves suffer mortality to leave behind open water, and relocate to a higher elevation.

A case study is provided of Lake MacLeod in Western Australia where monitoring documents one of the largest mortality events for mangroves ever recorded following a cycione and sustained flooding. Forest inventory and monitoring of mangroves is through this demonstrated to be an effective tool in understanding and managing mangrove forest decline.