Reproductive ecology of three ocypodid crabs II. Incubation sites and egg mortality

Abstract

AbstractMortality of eggs during incubation was estimated for three ocypodid crabs, Scopimera globosa, Ilyoplax pusillus and Macrophthalmus japonicus, and the influence of incubation sites was discussed. These crabs all lived in isolated burrows and fed on sediments during day time low tide. S. globosa and I. pusillus inhabited the upper intertidal sandflats, whereas M. japonicus inhabited the lower intertidal mudflats. Females of both S. globosa and I. pusillus remained in their plugged burrows without feeding throughout incubation and the mortality of eggs was low despite large broods relative to body size. On the other hand, females of M. japonicus fed actively on surface mud during incubation and the mortality of eggs was high despiite small broods relative to body size. In S. globosa and I. pusillus, the ovaries of ovigerous females were small until egg‐hatching, whereas in M. japonicus, the ovaries grew rapidly during incubation and females were able to produce consecutive broods. I conclude that incubation of eggs in burrows may be advantageous in species which inhabit the upper interidal sandflats, even though the crabs cannot forage during incubation, since otherwise their eggs would be exposed to strong heat stress and desication during the summer. Furthermore, such species may produce few large broods because of less frequent interruption of feeding than that associated with production of many small broods.