COMPONENTS OF RECRUITMENT IN POPULATIONS OF THE ACORN BARNACLE SEMIBALANUS-BALANOIDES (LINNAEUS)

Recruitment in marine species with pelagic larvae is sensitive to variation in larval supply, settlement rates, and early settler mortality, but the relative contribution of these processes to variation in recruitment is rarely known. We examined these components of recruitment success in two populations of the acorn barnacle Semibalanus balanoides (Linnaeus). Water column larval supplies differed by four-fold between populations. In the high larval supply population, benthic settlement sites were rapidly saturated with settlers. As a consequence of the saturation of settlement sites, daily settlement to remaining free space was intensified to 15 times higher than in the population with lower larval abundances. In sharp contrast to this augmentation of settlement rates, however, the saturation of settlement sites reduced differences between sites in the cumulative recruitment of calcified juveniles. Within-population patterns in settlement were also conspicuous but of lower magnitude than between-population differences. Settlement decreased with increasing tidal height but increased both with wave exposure and proximity to conspecifics. This local variation in settlement diminished over time at the high-settlement site as available settlement space was preempted. Larvae settle less selectively once preferred locations are saturated with settlers. Our results demonstrate that population differences in larval supply can lead to dramatic differences in recruitment within as well as among populations. Further elucidation of recruitment variation in marine species with planktonic larvae will require paying more attention to processes that dictate larval supply rates.