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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.

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Female blue crabs, Callinectes sapidus, mate in estuaries and undergo a seaward spawning migration to release larvae. According to the prevailing model, females with mature embryos use nocturnal ebb-tide transport (ETT) to move seaward, release larvae, and then reverse to nocturnal flood-tide transport (FTT) to move back into the estuary. We tested this model by examining the vertical migratory behavior of ovigerous and post-larval release female crabs. Simultaneous physical-biological data were collected for 38 d during Aug 2002-Sep 2002 in Bogue Sound, North Carolina. Crab water-column positions were determined with miniature internally recording pressure sensors. Local current and water properties were measured, and crab vertical migration times relative to observed currents were used to determine ETT and FTT behavior. Surface censuses of free-swimming crabs on 19 nocturnal ebbs were used to complement the intensive studies of individual crabs. The study found that (1) the pressure sensors had a measurable but small effect on swimming, (2) females migrated during day and night ebb tides, (3) females used ETT throughout embryo development, (4) ETT corresponded to the rate of decrease in water level (hydrostatic pressure), (5) larvae were released at high tide or when water level was falling, often within several hours of sunrise, and (6) post-larval release females continued ETT and did not switch to FTT. Thus, the data did not support the prevailing ETT-FTT reversal model. Rather, females continue ETT into coastal areas, releasing subsequent clutches farther seaward, which increases the potential for successful larval transport to favorable offshore developmental areas.For many marine species, successful recruitment entails adult migration out of an estuary and subsequent larval transport into an estuary. While substantial literature is accumulating on the latter process (e.g., Weinstein 1988; Crowder and Werner 1999;Epifanio and Garvine 2001), 1 To whom correspondence should be addressed. Present address: Environmental Fluid Mechanics Laboratory, Stanford University, Stanford, California 94305-24-4020 (jhench@stanford.edu). AcknowledgmentsWe thank Pia Moisander and Josh Osterberg for valuable assistance in the field. Sean Powers and two anonymous reviewers provided helpful suggestions on the manuscript.

Ovigerous blue crabs Callinectes sapidus use ebb-tide transport (ETT), a vertical migratory behavior in which crabs ascend into the water column during ebb tides, to migrate from estuarine adult habitats to coastal larval release locations. We have developed a detailed behavioral model of ovigerous blue crab ETT from previous laboratory and field studies and coupled this model to a hydrodynamic model of the Beaufort Inlet region of North Carolina. We have simulated the trajectories of migratory ovigerous crabs in the region and determined spatial patterns in migratory success, migratory speeds, the residence times of crabs in different regions of the estuary, and potential larval-release locations. Highly active crabs can start their migration from almost anywhere in the estuary and reach suitable larval-release locations within a typical 4 d migratory period, whereas crabs with lower activity levels can only reach suitable larval-release locations if they start their migration in the lower-to-mid estuary. Migratory speeds in the estuary range from <1 to > 8 km d -1. Crabs with lower activity levels are resident in the mid-to-upper estuary for relatively long periods of time, whereas highly active crabs are resident in the lower estuary and coastal ocean for most of the migratory period. Larval release is predicted to occur throughout the estuary and in the coastal ocean within ~5 km of Beaufort Inlet. Fisheries managers can use these spatial patterns to determine management strategies (e.g. spatial closures to fishing) that will protect migratory blue crab spawning stock in tidal regions effectively.