Passive larval dispersal is an important element in the life cycles of many marine benthic invertebrates in the coastal ocean. Transport processes that influence larval dispersal include advective dispersal, shear dispersion, Ekman veering, rotary or oscillatory tidal currents, a directional phase-lag in deep-water tidal currents, cross-current dispersion in noncollinear wave-current flows, vertical turbulent mixing, the inhibition of settlement by strong boundary shear stresses, and mass transport induced by shallow-water waves. I employed a variety of analytical techniques to examine the importance of these transport processes to passive larval dispersal. I later reexamined the analytical results with a time-dependent numerical model that included a second-order turbulent-closure scheme to determine vertical turbulent mixing.

Although steady currents are the most obvious agents of passive larval dispersal, the results from an analytical model suggested that steady currents typical of the coastal ocean are often too slow to generate sufficient vertical turbulent mixing to keep passively drifting, nonbuoyant larvae in suspension. Unlike steady currents, tidal currents typical of the coastal ocean often generate sufficient vertical turbulent mixing to keep passively drifting, nonbuoyant larvae in suspension during most of the tidal cycle. Tidal or tidally dominated currents share many of the same transport processes as steady currents, but their temporal variability gives rise to some additional dispersal characteristics. For example, the numerical model suggested that the timing of larval spawning relative to the time of tidal slack water can influence both the maximal spatial extent of dispersal and the patchiness of larval settlement.

One of the most significant conclusions of this study was that wind- generated surface waves are likely to be more important to larval dispersal and settlement than has been recognized previously. Surface waves can influence larval dispersal directly through wave-induced mass transport and indirectly by regulating larval settlement due to the high boundary shear stresses generated in the bottom boundary layer. The interaction of noncollinear waves and currents can also generate a component of cross-current dispersion and a net drift of larvae at an angle to the direction of the steady current.