The occurrence, mechanics and significance of burying behaviour in crabs (Crustacea: Brachyura)

Although the terms burrowing and burying are often used interchangeably in the literature, there are clear distinctions between these two types of behaviour in terms of their ecological, mechanical and physiological implications. Both types of behaviour are widely observed in the Brachyura. In comparison to the well-researched area of burrowing in crabs, information on burying is relatively dispersed. This review will examine the extent of burying behaviour in brachyurans, and the physiological and ecological consequences of the behaviour within the group. At least nine of the 50 families of brachyuran crabs have either been observed to bury in soft substrata or are suspected, on morphological grounds, of burying. There appears to be no specific morphological adaptations for burying in brachyurans, apart from those features associated with respiration whilst buried in the sediment. Buried individuals must ensure constant access to oxygenated water in the face of mechanical problems resulting from direct contact with the sediment, i.e., the threat of clogging. Burying taxa deal with this challenge through accessory respiratory channels and altered respiratory rhythms. The evolutionary implication of the burying habit is equivocal. Burying taxa are amongst the most speciose and numerically dominant brachyuran groups in marine systems, all reaching their greatest diversity and abundance in soft substrata. Burying may be an ancestral condition, with many of these groups evolving in habitats characterized by soft sediment.