Meyer, Alexander D.; Alan Hastings; and John L. Largier

The planktonic larvae of many coastal marine invertebrates swim vertically during dispersal to exploit variation in current strength and direction, food abundance and mortality rate throughout the water column and offshore. Prior studies have estimated the effects of vertical swimming upon larval dispersal using mathematical models. However, most such studies consider just a small number of predefined swimming behaviors despite evidence that even seemingly insignificant changes to these behaviors can dramatically alter predictions of larval delivery. Additionally, the concurrent effects of vertical swimming upon predation risk, feeding opportunities and energy budgeting are not well characterized. We used a simple mathematical model of larval dispersal in upwelling-favorable conditions to investigate how a continuum of swimming behaviors affect these quantities simultaneously. Within this continuum, we identified two categories of successful behaviors. 'Mean-onshore' behaviors deliver most larvae to coastal habitats, but offer limited opportunities for feeding and alongshore movement during dispersal. By contrast, 'mean-offshore' behaviors deliver fewer larvae to shore, but permit more feeding, alongshore movement, and, potentially, safety from nearshore hazards. No behaviors considered achieved the benefits of both categories. We hypothesize that mean-onshore behaviors are advantageous for species with non-feeding larvae or sparse adult populations, while mean-offshore behaviors are advantageous for species with feeding larvae or crowded adult populations. Our results underscore the importance of considering how behavior interacts with environmental structure and individual biology while studying dispersal in marine and other ecosystems.