Relevance of mangroves for the production and deposition of organic matter along tropical continental margins.

Mangroves are highly complex ecosystems occupying a major part of tropical coastlines. High primary productivity, efficient biological nutrient recyling and a permanent exchange with terrestrial and marine ecosystems are their common features. Despite the high production and export rates of leaf litter, mangrove detritus has been reported to be of minor importance in sustaining marine food webs. The geographical distribution of mangrove-derived organic matter (OM) in marine sediments is found to be restricted to the vicinity of its source. Dissolved nutrient inputs from mangroves and rivers may fuel the production of marine OM. In this paper we assess the relevance of mangroves for the production and sedimentation of OM in the tropical coastal ocean based on data available from the literature and our own research results. We estimate the rates of carbon accumulation in mangrove sediments and of carbon export to the coastal seas. From the rates of litter fall and export we calculate carbon accumulating in mangrove sediments to be in the order of 23x10(12) g C per year and mangrove carbon introduced into the coastal ocean to be in the order of 46x10(12) g C per year. They account for about 11% of the total input of terrestrial carbon into the ocean and 15% of the total carbon accumulating in modern marine sediments.