Causes and Consequences of Variable Recruitment in the AcornBarnacle, Semibalanus Balanoides

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While it is widely believed that variation in recruitment (the introduction of new individuals to a population) can influence the structure and dynamics of marine populations, the specific causes and consequences of variable recruitment are poorly known for any species with planktonic larvae. The present evidence suggests that recruitment of the acorn barnacle, Semibalanus balanoides, is strongly influenced by oceanographic features that dictate larval supply. Moreover, the resulting recruitment variation hypothetically can strongly influence the distribution, abundance, demography, and genetic structure of barnacle populations in previously unsuspected ways. On the basis of these preliminary data three young scientists Drs. Gaines, Bertness and Geyer will initiate a regional study to examine the links between a specific coastal oceanographic feature (embayment flushing time), water column larval abundance, benthic recruitment variation, and population processes in Semibalanus balanoides. Specifically, this investigation will: 1) examine the hypothesis that variation in flushing rates among sheltered bays and among years generates variation in larval abundance and shoreline settlement rates, 2) evaluate experimentally the relative importance of this regional and temporal variation in recruitment to the distribution, abundance, and demography of barnacle populations, and, 3) test the hypothesis that variation in larval retention among sheltered bays predictably affects the degree of local adaptation of barnacle populations by altering rates of gene flow. This work will address critically important issues in our understanding of the ecology and evolution of species with complex life histories.