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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.

The return of Panulirus cygnus larvae to the coast of Western Australia after nearly a year at sea and its modulation by ocean currents were addressed with an individual-based larval-transport model. The simulations implied that offshore wind-driven transport of larvae is balanced by onshore geostrophic flow. Additional simulations revealed that vertical migration behaviour was essential to larval survival through its impact on advection. The six years simulated include two of high, two of low, and two of average puerulus settlement. The most robust interannual difference of the simulations was that, when coastal sea level was low and the Leeuwin Current was weak, more early-stage larvae were lost to the north and west under the influence of the wind. Conversely, many late-stage model larvae were carried south of the fishery in years when the Leeuwin Current was strong. The fraction of model larvae remaining or arriving offshore of the fishery and metamorphosing was essentially constant from year to year, so the variation in observed puerulus settlement was not explained by the model. The results imply that the nonadvective effects of fluctuations in the Leeuwin (e.g., on temperature and primary production) were primarily responsible for the high variation in natural settlement.

Observations of the South Pacific Deep Western Boundary Current from the World Ocean Circulation Experiment Pacific current meter array 9 (WOCE PCM‐9) current meter array are compared with the Los Alamos National Laboratory high‐resolution global ocean model. A simple integration of PCM‐9 velocity yields a mean northward transport of water deeper than 3000 m that is some 5 times greater than the model mean transport of 3.35 × 106m3 s−1. The low modeled abyssal transport suggests a poor simulation of the mean thermohaline circulation. However, model and observed transport variability correlate significantly. Space‐time spectral analysis shows planetary waves are responsible for most of the variability and are resolved well in the model. The details of interaction of the long waves at the western boundary are different in model and data. The model reflects these waves predominantly as planetary short waves, which decay over the region 600–800 km east of the Kermadec Ridge. PCM‐9 has a higher proportion of energy as topographic waves along the Kermadec Ridge. These two classes of waves are associated with the two observed zonal scales in the boundary current. The model results can be separated into vertical modes. Baroclinic energy is found at all timescales, including those too short for free baroclinic waves. The baroclinic flow correlates with the barotropic so as to enhance surface, and reduce abyssal, kinetic energy. This is the signature of planetary wave scattering at the submerged western boundary ridge, and results in enhanced baroclinic wave energy in the Tasman Sea.

The spatial and temporal variability of the East Australian Current (EAC) is investigated using 6 years (1993–1998) of surface geostrophic stream function from an optimal interpolation of altimeter sea surface heights and velocities derived from tracking thermal features in satellite imagery. Variability appears as a series of cyclones and anticyclones propagating southwestward and westward with periods between 90 and 180 days. The behavior of the variability changes over the 6 years. Energy in the mesoscale frequencies moves slowly south and diminishes with more westward propagation in the region where the current separates from the coast. We find no evidence for a consistent forcing of the EAC by mesoscale signals propagating westward from the South Pacific basin. We suggest that the observations are consistent with variability originating between 32°S and 35°S through intrinsic instabilities of the current.