CONSIDERATIONS IN ESTIMATING LARVAL DISPERSAL DISTANCES FROM OCEANOGRAPHIC DATA

Determination of larval dispersal distances and larval origins is a central challenge in contemporary marine ecology. In this work, the larval dispersal problem is discussed from the perspective of oceanography. Following formulation of the advection- diffusion model, the importance of scale is argued. When considering dispersion parameters at the appropriate population scales, advection is usually weaker than initially anticipated (and often used), and diffusion is stronger than typically used in model studies. Focusing attention on coastal populations, the importance of retention zones is described, and the more general existence of a coastal boundary layer is discussed. The coupling of cross- shore and alongshore dispersion results in a nonlinear relation between alongshore dispersal distance and larval planktonic period for dispersion in a sheared flow. Thus, small changes in cross-shore dispersal, whether due to environmental differences or larval behavior result in significant differences in alongshore dispersal. Finally, the interplay between advection and diffusion is explored, showing the importance of adequately representing the diffusive effects that mitigate alongshore advection. In most cases, diffusion acts to prevent ''wash- out'' of a population and allows for more flexibility in the size and spacing of effective marine reserves. Future challenges must bring oceanographers and ecologists together around specific dispersal problems if there is to be a significant improvement in the notable absence of hard data in this field of enquiry.