Burrow-orientated activity in the ocypodid crab, Dotilla fenestrata, living in a mangrove swamp

The behavioural repertoire of the Scopimerinae crab, Dotilla fenestrata, is the result of a juxtaposition of rigid and plastic patterns, as an adaptat ion to the intertidal habitat. On the one hand, the activity of D.fenestrat a can be classified in a number of stereotyped behavioural patterns, the oc currence of which may change throughout the low water or on the basis of th e crabs' relative size, according to an expected schedule. For example, dig ging is more pronounced in larger individuals and mostly occurs when the cr ab emerges or just before it seals itself inside the burrow at the flooding tide. In contrast, maintenance of the burrow is a constant behaviour. Feed ing rate, estimated from the number of pseudofaecal pellets emitted, is con stant both throughout low water, with the exception of noon when it decreas es, and with the feeding crab's size. The behavioural patterns that assure water uptake and temperature regulation (sponging and visits inside the bur row) are more frequently performed around noon. Agonistic patterns are most ly performed by larger individuals; the rate of aggression by resident crab s, against neighbours but mostly against smaller passers-by, increases with the flooding tide. On the other hand, for a surface deposit-feeder like D. fenestrata, plastic behaviour is mainly caused by the unpredictable distri bution of food over the emerged platform. The result is a number of adaptiv e flexible behaviours, like: (1) the presence within the same population of both burrow-centred crabs and wanderers; (2) the construction by the forme r subpopulation of two types of burrows (feeding-trench burrows and igloos) ; and (3) significant differences in the behavioural budgets of the inhabit ants of the two burrows. The ability to 'switch' modes of activity allows r esponses to both the predictable and unpredictable elements of intertidal e nvironments, the mangrove swamp included.