Interactions between larval behavior and local hydrography affect settlement patterns of the crab, Cancer gracilis, in northern Monterey Bay. An upwelling shadow is a typical feature of northern Monterey Bay during upwelling season ({dollar}sim{dollar}March to August) and is a dynamic response to upwelling north of the bay as cold, upwelled water is advected into the bay, recirculated, entrained and subsequently heated. This upwelling shadow is thin ({dollar}<{dollar}15 m thick) vertically trapped, warm patch of water that behaves much like an estuarine plume. A quasi-persistent (weeks to months) front with both shear and buoyancy components separates the upwelling shadow from recently upwelled water offshore.; Within this front, dense aggregations of the scyphomedusa Chrysaora fuscescens occur. Uniformly oriented horizontal swimming of these medusae further minimizes the swarm's dispersal. Megalopas of the brachyuran crab Cancer gracilis tend to cling to drifting and slow-moving materials, and they are accumulated on the jellyfish where they may remain for several months as juveniles. While on medusae, crabs probably experience protection, enhanced growth, increased dispersal and decreased loss due to offshore advection.; The jellyfish-front interaction causes most juvenile crabs to settle on the sea floor {dollar}sim{dollar}4-8 km from shore during upwelling seasons (March-August). In the absence of jellyfish swarms, as during the 1992 El Nino Southern Oscillation, Cancer gracilis settles much closer to shore. This study provides evidence that specific larval behavior is an integral component of the physical-biological interactions which determines juvenile settlement patterns.
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