DISPERSAL OF JUVENILES AND VARIABLE RECRUITMENT IN SESSILE MARINE SPECIES

MARINE species commonly have broadly dispersing juveniles called larvae. Their return to the adult populations is highly variable1-3, often generating large fluctuations in population size4-6, yet the causes of the variation are poorly understood. Historically, attention has been focused on the roles of variable reproductive output by adults and variable mortality during larval development7,8. The limited success of these factors as general explanations prompted a more recent focus on the influence of variable transport of the larvae9-13. Here we show that nearly a decade of settlement variation of the barnacle, Semibalanus balanoides (L.), closely matched predictions based solely on a transport hypothesis: differences in transport generate recruitment variation by determining whether larvae complete development near a favourable habitat. The irregular nature of coastlines, particularly the presence of bays and estuaries, generates substantial regional variation in coastal transport that may generate correspondingly large variation in recruitment to marine populations.