Larval Mortality from Offshore Mixing as a Link between Precompetent and Competent Periods of Development

Abstract

A model of larval dispersal of coastal benthic invertebrates is proposed: Eddy mixing spreads larvae in the onshore-offshore direction during the period before competence to settle and continues to take larvae both onshore and offshore after they are competent to settle; predators kill larvae during both precompetent and competent periods. Distribution of larval stages of several species are consistent with the model. The model correctly predicts (1) increased competent period with increased precompetent period in comparisons among species, and (2) a competent period greater than or equal to the precompetent period. The model predicts a decrease in the ratio of competent to precompetent period as precompetent period increases, which is not apparent in available data. Also, some observed competent periods are longer than those predicted by the model. Reasons for these departures from predictions are suggested. The model differs from previous optimization or maximization models for planktonic larvae by including onshore-offshore mixing and thereby linking selection on the precompetent and competent periods.