Response of Mangrove Shorelines to Sea-level Change

Abstract

The response of mangrove shorelines to sea-level change is a function their overall sediment budget. Whereas mangroves have often been viewed as a source of organic productivity which is supplied to adjacent estuarine waters, they are generally considered a sink for sediments. Though often displaying a shore-parallel zonation of mangrove species, this need not indicate succession, or that the shoreline is prograding. Despite pronounced zonation, such as in southwestern Florida where mangroves occur adjacent to freshwater wetlands of the Everglades, interpretations based upon stratigraphy have ranged from a view of mangroves as builders of land, to one of retreat as a result of sea-level rise over the past few thousand years. Fossil mangrove material may be used to determine the pattern of fluctuations of sea level over the late Quaternary, and may also indicate the nature of response of mangrove shorelines to past sea-level changes. Mangrove sediments provide a relatively good record of sea-level rise, particularly where there has been a rapid supply of inorganic sediment to the coast, but are poorer indicators of sea-level fall or periods of stable sea level. The function of mangrove ecosystems differs in different environmental settings, and a framework is proposed within which to view the role of mangroves. Sedimentation beneath mangroves modifies the way in which the shoreline responds to changes in sea level, and the timescale over which sedimentation rateis considered is Iikely to influence the way in which mangroves appear to have responded. Future changes are to be expected on mangrove shorelines, but differentiating between natural changes, human-induced changes, or responses to global environmental change will be difficult, and may differ between locations.