Extreme spatial variation in the growth and reproductive output of the acorn barnacle Semibalanus balanoides

Geographic vanahon in secondary production can profoundly influence populahon and community processes yet is rarely studied in benthic manne organisms In this paper w e document stnlung vanahon withln and among locations in the growth and reproducbve output of the acorn barnacle Sernlbalanus balanoides and discuss the potential consequences of our results on understanding recruitment and other population processes Within Narragansett Bay (Rhode Island, USA) barnacle growth and reproduction is far greater than at nearby open coast locations At comparable tidal heights recruits in the Bay grew to nearly twice the basal diameter and had almost 10 times the reproductive output compared to recruits on the open coast Transplant experiments suggest that the high secondary production of Bay barnacles is largely a phenotypic response to high primary production Within-and among-site patterns in barnacle secondary production associated with enhanced flow velocities were also conspicuous Barnacles at low tidal heights, in habitats exposed to large tidal currents and in waveexposed habitats had higher growth and reproduction than barnacles at hlgher tidal heights or habltats with lower velocities Water column food concentrations and fluid velocities both strongly influence barnacle growth and reproduction through their combined effects on the flux of food to indi\~lduals Our results imply that predictable variation in food supply rates may lead to important and equally predictable consequences on regional larval production and the density-dependent dynamics of adult benthic populations