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Water movement is a critical factor driving the ecology and evolution of marine life. Hydrodynamics can constrain biological processes, yet many organisms are also adapted to or exploit particular flow regimes. We have been studying the relative importance of physical and biological mechanisms controlling (1) larval dispersal, (2) larval settlement, and (3) feeding of benthic (bottom-dwelling) invertebrates. Laboratory and field research capitalizes on the burgeoning technologies for measuring flow, and organisms moving within it. Most studies have revealed passive (physical) and active (behavioral) phases to a given biological process. For example, the flow largely controls larval supply to the bed. After touchdown, larvae actively investigate the surface and elect to stay or leave. Because exploration often occurs in the direction of flow, fluid dynamics constrains habitat perusal. Moreover, site selection criteria can include features of the near-bed flow regime, as well as of the substratum. Sufficiently high turbulence can, however, obviate the entire settlement process. Ongoing research expands these interdisciplinary studies to include chemical mechan isms as well. For example, we are evaluating the relative importance of dissolved versus adsorbed chemical cues during larval settlement of a sea slug living on an obligate algal host; and the role of near-bed flocculated material as a temporary venue for larvae settling onto soft sediments.