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The intensity of small‐scale fluid motions varies among coastal seascapes, which could drive species‐specific behavioral adaptations in planktonic larvae. For example, inlets and estuaries typically have stronger turbulence and weaker surface gravity waves than the continental shelf. In the Mid‐Atlantic Bight, eastern mudsnails (Ilyanassa obsoleta) inhabit inlets and estuaries, whereas threeline mudsnails (Ilyanassa trivittata) inhabit the continental shelf. The two species' larvae respond differently to hydrodynamic signals: both hover in calm conditions and sink in response to vorticity, a signal of turbulence, while only shelf snail larvae also sink and swim up in response to accelerations, which can be large under waves. We investigated how these observed larval behaviors and more idealized ones affect retention and settlement in estuaries using numerical experiments. Virtual larvae were released and tracked in a regional model of Delaware Bay and the adjacent shelf. Behaviors that involved downward motions, including vorticity‐induced behaviors, helped concentrate larvae near the bottom and enhanced retention in the bay. In contrast, behaviors that involved upward motions, including acceleration‐induced behaviors, promoted export onto the shelf. Compared to neutral buoyancy, the vorticity‐induced behaviors also conferred longer residence times in the bay, higher settlement probabilities, and shorter pelagic larval durations, all of which would be advantageous to estuarine species. This integration of larval observations with simulations provides evidence that behavioral responses to coastal physics can reduce larval mortality by enhancing retention and settlement in native seascapes.

Ocean warming has predictably driven some marine species to migrate polewards or to deeper water, matching rates of environmental temperature change (climate velocity) to remain at tolerable temperatures. Most species conforming to expectations are fish and other strong swimmers that can respond to temperature change by migrating as adults. On the Northwest Atlantic continental shelf, however, many benthic invertebrates’ ranges have instead shifted southwards and into shallower, warmer water. We tested whether these ‘wrong-way’ migrations could arise from warming-induced changes in the timing of spawning (phenology) and transport of drifting larvae. The results showed that larvae spawned earlier in the year encounter more downwelling-favourable winds and river discharge that drive transport onshore and southwards. Phenology and transport explained most observed range shifts, whereas climate velocity was a poor predictor. This study reveals a physical mechanism that counterintuitively pushes benthic species, including commercial shellfish, into warmer regions with higher mortality.

A REMUS 600 autonomous underwater vehicle was used to measure turbulent mixing within the far‐field Chesapeake Bay plume during the transition to upwelling. Prior to the onset of upwelling, the plume was mixed by a combination of energetic downwelling winds and bottom‐generated shear resulting in a two‐layer plume structure. Estimates of turbulent dissipation and buoyancy flux from a nose‐mounted microstructure system indicate that scalar exchange within the plume was patchy and transient, with direct wind mixing constrained to the near surface by stratification within the plume. Changing wind and tide conditions contributed to temporal variability. Following the separation of the upper plume from the coast, alongshore shear became a significant driver of mixing on the shoreward edge of the plume. Turbulence measurements made by an autonomous underwater vehicle reveal that the wind‐driven offshore movement of a coastal river plume leads to intermittent and patchy mixing of plume and shelf waters. These novel, high‐resolution observations highlight the importance of capturing transient features when determining the fate of rivers on continental shelves. Microstructure measurements from an AUV reveal transient turbulent mixing in the far‐field of a plume during upwellingSpatial and temporal variability of dissipation and mixing is related to changing wind and tide conditionsAlongshore shear was as important, at times, as cross‐shore shear for driving mixing within the plume as it separated from the coast