Feeding ecology of the mangrove crab Neosarmatium smithi (Crustacea: Decapoda: Sesarmidae)

Abstract

Consumption experiments showed that the mangrove crab Neosarmatium smithi H. Milne-Edwards preferred litter of the mangrove Ceriops tagal decayed for some weeks. Determination of assimilation efficiencies, using a 72% sulfuric acid insoluble residue as indigestible marker, revealed that N. smithi assimilated little of the components of a 2 wk old litter diet, but that assimilation efficiencies (carbon, nitrogen, caloric content, organic matter) ranged from 30 to 60% when fed 4, 6 or 8 wk old litter. These values must be treated with caution because the validity of using a 72% sulfuric acid insoluble residue as an inert marker in determining assimilations in mangrove studies, as used here, is questioned. Due to the extremely high carbon-nitrogen ratios of the litter, these diets fall well below accepted nutritional standards. An additional source of nitrogen in the diet was determined by gut content analysis to be small crustaceans. N. smithi is not a direct link in the ecosystem food chain. Carrying the leaf litter into their burrows - where the leaves decay, are subsequently consumed, and faeces are produced - the crabs substantially reduce export of leaf litter by tidal transport and regenerate nutrients for other small invertebrates and the mangroves themselves.