Microbenthos, meiobenthos and fiddler crabs: trophic interactions in a tropical mangrove sediment

Aspects of the feeding ecology of Uca vocans and Uca polita from tropical mangroves were studied. Gut analysis revealed that microheterotrophs were the major food source for both species although U. polita also ingested small numbers of microalgae. No evidence was found for the ingestion of meiobenthos. Based on measurements of feeding rate and mass of feeding pellets produced it is estimated that the U. vocans population forages 43 % of the sediment surface during a low-tide feeding period of 2 to 2.5 h. The corresponding figure for U. polita is 22 %. Abundance of meiobenthos increased 2 to 5-fold when crabs were excluded from the sediment. It is suggested that avoidance by downward migration and/or competition for food resources may account for this difference.