MEPS 142:147-163 (1996)  -  doi:10.3354/meps142147

Veligers spawned by adults collected from 3 different populations (Georges Bank, Passamaquoddy Bay and Mahone Bay, all on the northeastern coast of North America) of giant scallops Placopecten magellanicus were maintained for 2 mo in replicated, 9.5 m deep, polyethylene mesocosms with a 1.5°C thermal gradient at mid-depth and a 12/12 photoperiod. The populations came from varied hydrographic regimes that might require veligers to have different vertical migration patterns if they are to be in an appropriate area for settlement when they reach competency. Veligers from all populations were found in shallower depths at night than during the day, developed strong bio-convective cells when numbers were high at the surface and were seldom found below the thermocline until about 21 d after spawning. Under similar conditions, veligers from the 3 populations exhibited significantly different vertical migration patterns and depth distributions. These patterns of vertical distribution are unlikely to be due to differences in buoyancy, growth rate, food density, settlement preference or mesocosm effect, and they differ substantially from patterns of mussel veligers raised according to the same protocol. Such differences may reflect selection for different behaviors in different populations, arguing for an active and genetically controlled component to vertical movements of scallop veligers. The observed patterns of vertical distribution could produce marked differences in horizontal transport in the various physical regimes; increased self-recruitment seems the most likely explanation for the intense selection required to fix such behavior in populations.

Scallops · Recruitment · Retention · Predator avoidance · Tidal phase · Moon rise