POPULATION ECOLOGY OF THE SAND-DWELLING HERMIT-CRAB DIOGENES-NITIDIMANUS .4. LARVAL SETTLEMENT

Settlement patterns of juveniles of the sand-dwelling hermit crab Diogenes nitidimanus Terao were examined in 1982 and 1983, Newly settled crabs were found from mid-August to the beginning of December, and peak settlement occurred in September. Crabs settled near the water level of extreme low water spring tide (ELWS) in the study area, where small, vacant shells were abundant. The density of settled crabs and that of small vacant shells were positively correlated in August, November and December. The recently settled crabs were not found on the upper flat (about 1 m above ELWS) or in the subtidal zone 5 m below the ELWS, in spite of the abundance of small shells at those locations. Small, vacant shells were introduced into the lower intertidal zone of the study area, and their presence may have resulted in an increase in the number of settled juveniles. This possibility suggests that shortage of small shells limits the settlement of hermit crabs.