Development of Mangrove Swamps Behind Beach Ridges, Grand Cayman Island, West Indies
Mangrove swamps often occur in association with sand barriers, and in some instances these may totally isolate them from tidal inundation. Two areas of non-tidal mangrove on Grand Cayman Island are described, Prospect and South Sound mangrove swamps, both of which are occluded behind beach ridges of coralgal sand. The vegetation of these swamps resembles that of tidal mangrove swamps and probing and coring of thicknesses of >2 m of mangrove peat indicate that the early stages of development of these areas have been similar to the development of mangrove swamps elsewhere on Grand Cayman; initial establishment and subsequent expansion of mangroves have occurred during the late Holocene as the island has undergone relative submergence. The formation of beach ridges, which occurred during at least two episodes in Prospect mangrove swamp, totally isolated the swamps and altered their flooding regime. Flooding at present is seasonal and by freshwater, following high rainfall, and the swamps gradually drain through the dry season. Substrate characteristics differ between tidal and non-tidal mangroves; in the occluded swamps salinity concentrations in the peat are low in the upper 20 cm but increase with depth. It is also demonstrated that the elevation of the swamp substrate varies from 9 cm below mean sea level (a datum approximating true mean sea level) to 42 cm above mean sea level in the tidal mangrove, and from 22 cm to 70 cm above mean sea level in the non-tidal mangrove. The swamp floor is significantly higher in the occluded mangrove; much is beyond the elevation reached by the highest tide. It is suggested that not only have the growth of mangrove species and the accumulation of peat continued in these isolated mangrove swamps but that accretion of the swamp substrate has been more rapid because direct tidal flushing, and consequently tidal export of organic matter, is absent and decomposition is less rapid.
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Document Type: Research Article
Publication date: 1983-10-01
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