MOVEMENT PATTERNS AND MIGRATIONS IN CRABS - TELEMETRY OF JUVENILE ANDADULT BEHAVIOR IN CALLINECTES-SAPIDUS AND MAJA-SQUINADO

Late stage juveniles and adults of Callinectes sapidus in Chesapeake B ay, USA, and Maja squinado off the Ria de Arousa, Spain, were compared for ontogenetic changes in movement patterns (speed, distance, orient ation) and habitat selection (depth, substrate) using ultrasonic telem etry and published information. After settling in submerged grass beds in the fewer Bay, 2O-mm juvenile C. sapidus disperse long distances i nto low salinity sub-estuaries to feed and grow to maturity in two yea rs. Within the Rhode River sub-estuary, juvenile C. sapidus moved with a mean speed of 12 m h(-1) in nearshore shallows (1.1 m); whereas adu lts averaged 24 m h(-1) in the deeper (2.9 m) channel areas and moved freely in and out of the main estuary. Individuals of both life stages exhibited a pattern of slow meandering (juveniles, 2 m h(-1), adults 10 m h(-1)) within a limited area, alternating with faster, directiona lly-orientedmovement Both stages >50 m h(-1)) between meandering sites . Juvenile and adult males over winter in deeper water nearby, while i nseminated females migrate long distances into high salinity areas to incubate the eggs. Callinectes sapidus completes the migration cycle o nly once per 2.5-y generation. Maja squinado settles on reeks in shall ow kelp forests in the coastal zone, where they grow to maturity in 2 y. Juveniles moved slowly (0.5 m h(-1)) while meandering without direc tional. orientation on shallow (4 m) small patch reefs during summer. After the pubertal moult in summer, adults also meandered slowly (1 m h(-1)) mostly on rocks at slightly greater depth (7 m). In late summer and autumn, newly mature and older adults moved with directional orie ntation into deeper (10-40 m) water for the winter, until migrating ba ck to the shallows for the summer; whereas juveniles remained inshore on rocks for the winter. Adult M. squinado live several years after pu berty and complete the seasonal migratory cycle several times during t heir lives. Despite marked differences between the two species in life histories and habitats, their similarities in behaviour and shifts in habitat utilization during ontogeny reflect adaptation to similar sel ective pressures. For both species, juvenile movement and habitat sele ction primarily indicates adaptation to intense predation pressure and growth optimization; whereas adult behaviour and migration indicates relaxed predation pressure but optimization of energy needs and site o f larval release.