Factors affecting the burrowing behaviour of Helice tridens (Grapsidae) and Macrophthalmus japonicus (Ocypodidae) in an estuary of northeast Japan

Abstract

Helice tridens (De Haan) (Grapsidae) and Macrophthalmus japonicus (De Haan) (Ocypodidae) build separate burrows in reed marshes and muddy tidal flats, respectively, in the brackish-water estuaries of northeast Japan (38°11′N, 141°48′E). Habitat segregation between burrows of these two species was analysed by comparing the density of burrows of both species in their natural habitats, and on tidal flats subjected to various types of artificial treatment, in the summer of 1981 and 1982. Baskets, containing many stones, were placed on the ground in the reed marsh, tidal flat and creek and attracted many individuals of H. tridens, but not M. japonicus. When stones were placed on an area of tidal flat, H. tridens frequently formed burrows at the border between the stones and mud, suggesting that burrowing of H. tridens was related to the presence of solid substances lying on the ground, such as stones and shoots of the reed Phragmites australis (Cav.) Trin. In closed systems on the tidal flat and reed marsh, H. tridens and M. japonicus were able to construct burrows in both substrata regardless of high or low frequency. Moreover, it was recognized that H. tridens prevented the burrowing of M. japonicus in these closed systems. These results suggested that habitat segregation between H. tridens and M. japonicus burrows was caused primarily by an exclusive interaction between individuals of these two species.