The influence of diel vertical migration on zooplankton transport and recruitment in an upwelling region: estimates from a coupled behavioral-physical model

ABSTRACT

Diel vertical migration (DVM) is a common zooplankton behavior in which organisms reside in surface or near-surface waters at night and at deeper depths during the day. In many upwelling regions, DVM reduces the transport of organisms away from the region. It is unclear, however, what role DVM plays in recruitment (the arrival of larvae or juveniles to locations where they will become reproducing adults) to upwelling regions. In this study, we estimate the influence of DVM on zooplankton transport, the level of recruitment of locally produced propagules (self-recruitment), and sources of recruits in the upwelling region near Monterey Bay, California, by simulating the trajectories of fixed-depth and vertically migrating organisms with a drifter-tracking algorithm driven by climatological velocity fields from a three-dimensional hydrodynamic model. Our simulations suggest that DVM into subsurface poleward and onshore currents during the day does not fully compensate for equatorward and offshore transport in the surface Ekman layer at night and does not retain zooplankton in the Monterey Bay region. Our simulations also suggest that DVM decreases the ability of zooplankton to return to the region after being transported away and shifts source regions for recruits closer to the bay. While DVM does not appear to substantially increase the potential for self-recruitment to the region, this study indicates that other mechanisms, such as transport during non-upwelling periods, continuous transport below the surface, increases in mean transport depth over time, or seasonal changes in hydrography, may still enable relatively high levels of self-recruitment to this highly advective region.