The role of life history and behavior in explaining unionid mussel distributions

The São Paulo shelf ranges from ~23°S to 25°S, comprising nearly 622 km of shoreline. This region sustains historical landings of the tropical arrow squid Doryteuthis plei. As in other coleoid cephalopods, the broodstock dies following spawning and the continuance of the population relies exclusively upon the survival of the paralarvae, which are very sensitive to oceanographic conditions. As a first step towards the understanding of paralarval transport, the shelf area was evaluated in terms of retention/dispersion potential. A Lagrangian particle-tracking Individual-Based Model was set up using a 3D Princeton Ocean Model model forced with in situ data obtained from July 2009 to July 2011. Neutrally buoyant particles were released every first day of every month in the model, and tracked for 30 days. The retention potential was high for particles released from the bottom all over the study area from the coast to the shelf break (200 m isobath). Offshore losses showed a marked seasonality. Regarding inshore losses, the percentage of particles beached was constant year round and smaller than offshore losses, being higher south of 24°S. Simulation results seem to agree with present knowledge of the reproductive behaviour of the species in the region.