Habitat segregation of two dotillid crabs Scopimera globosa and Ilyoplax pusilla in relation to their cellulase activity on a marsh-dominated estuarine tidal flat in central Japan

This study aimed to clarify the relationship between cellulase activity and habitat segregation for two dotillid crabs - Scopimera globosa and Ilyoplax pusilla - on the marsh-dominated Tanakagawa tidal flat in central Japan. Both species are deposit feeders, and represent the dominant crab species in the study area. S. globosa was found to occur within sandy sediment habitats on the tidal flat, while I. pusilla occurred in both muddy sediment on the tidal flat and salt marsh habitats. This study was the first to detect cellulase activity in dotillid crabs. Cellulase activity was detected for both species; I. pusilla was found to exhibit significantly higher activity than S. globosa. Organic matter content, which is known to have a strong positive correlation with the cellulose content of sediments in estuarine areas, was higher in the sediments of muddy and salt marsh habitats compared with those in sandy habitats. Our findings indicate a close relationship between the habitat segregation of these two crabs and their cellulase activity. Given that cellulose is abundant in refractory organic materials and is a major component of food resources in tidal flat sediments, it is likely that these two crab species, especially I. pusilla, would play an important role in material cycling in tidal flat and estuarine areas.