Abstract

Recent research on Indo–Pacific mangroves has confirmed the significant role played by grapsid crabs in the structure and function of these ecosystems. Through the feeding activities of the crabs, large proportions of organic matter production, i.e. mangrove leaves, are recycled within the forest. This initial retention of production in the forest refines earlier estimates of tidal export from the mangroves. Crab-processed organic matter could also form the basis of a coprophagous food chain involving small invertebrates, or be re-exported as micro-particulates. Differential consumption by crabs of mangrove propagules also affects mangrove community structure by diminishing the relative abundance of species whose propagules are preferred foods. Bioturbation by the crabs also results in changes in surface topography, particle size distribution and degree of aeration and, thus, the concentration of phytotoxins in the substratum. Such changes could affect growth and production of the mangroves. Growth and reproduction of the crabs may in turn be influenced by the associated mangrove species, mainly through the provision of food. The semi-terrestrial and air-breathing habit of the grapsid crabs probably makes them tolerant of deoxygenation caused by organic enrichment, but development of the landward mangroves will strongly affect survival of the crabs.