Role of ocypodid crabs on carbon and nitrogen cycle in a tidal flat

Abstract

Many kinds of benthic organisms in tidal flats are considered to be involved in the purification of organic load. Among them, ocypodid crabs are expected to play an important role due to their high population density in sandy tidal flats. We estimated the organic ingestion of the crabs in Hitotsuba Lagoon within Miyazaki Port in all seasons throughout the year of 2003. Three dominant species, Uca lactea, Ilyoplax pusilla, and Scopimera globosa, and their feeding pellets were collected by quantitative methods. Their habitats were 3500, 1500 and 20750-26750 m 2, respectively. The maximum accumulations of their feeding pellets were 944, 486 and 2266 g m -2 d -1, respectively. The original bottom sediments contained organic matter of less than 5.0 mg Cg -1 and 0.5 mg Ng -1, and the loss compared to the feeding pellets was 5-80%. These three species ingested 3.36, 0.18 and 1.67 g Cm -2 d -1, 0.416, 0.024 and 0.086 g Nm -2 d -1 from the bottom sediments, respectively. Their total ingestion was estimated to be about 13 kg Cd -1 and 1.4 kg Nd -1 in this lagoon, which might be equivalent to 7% of the organic load from outside of the lagoon.