Experimental studies of particle ingestion by the sand fiddler crab Uca pugilator (Bosc)

Particle ingestion by the sand fiddler crab Uca pugilator (Bosc) was investigated using clean sand sediment inoculated with glass and plastic beads. For all bead types, the number ingested was positively correlated with the initial sediment bead concentration. Ingestion efficiency, however, was inversely correlated with bead diameter, weight, and initial sediment bead concentration. The latter result suggests that the particle sorting mechanism can be saturated at high substratum particle concentrations. Crab size was directly related to the efficiency at which large beads were ingested, but had no effect on the ingestion of small beads. Ciliates, unbound bacteria, and bacteria attached to sand grains were ingested with high efficiency, but the crabs did not preferentially ingest live over inert particles. Other results suggest that maximization of food intake by sand fiddlers occurs at the habitat patch level rather than at the level of particle ingestion. Supporting this view is the observation that inert particles which were ingested with high efficiencies did not stimulate crab feeding. Sediment harvesting rates were inversely related to substratum organic and silt concentrations suggesting that sand fiddlers can control ingestion rates by regulating sediment harvesting rates