mangrove communities are considered

mangrove communities are considered as important elements in coastal ecostems in the tropics beacause they are known to be highly productive systems which function as nursery grounds to many commercially important marine species . In most countries of the tropics, crabs and mollluscs dominant the mangrove forests. Smith et al. have shown that the sesarmid crabs occupy a keytone position in australian mangrove forest. The potential role of crabs in cycling of meterial in mangroves communities and their ability in conserving nutrients whith in the forest are well recognized. Smithet al (1991 showed that reductions in crabs abundance had led to increased sulphide and ammonium concentration in the soil and to reduced productivity and reproductive output by the mangroves. Bertness showed that the reduction of fiddler crabs density for a single growing season decreased above ground production by 47% and burrowing by the crabs increased soil drainage, soil oxidation-reduction potential and theinsitu decomposition of below ground plant debris.