Growth and production of the barnacle Balanus amphitrite in an intertidal area affected by sewage pollution

A low-density, intertidal population of the barnacle Balanus amphitrite was studied close to a sewage outfall near Quequen, Argentina. Barnacles were individually followed during 3 consecutive years. Growth rates observed in the present study (orifice length 4.9-5.1 mm at the end of the first year) were remarkably lower than values previously reported for this species. A Von Bertalanffy growth equation was fitted to length-age data (K = 0.4-0.5, L-infinity = 8.5-8.8, T-0 = -0.5 to -0.7). Growth and production were higher in summer/autumn than in winter/spring. The production/biomass ratio fluctuated between 0.3 and 0.4 for the whole population, but was highest (1.8-1.9) during the first year of benthic life. Based on analysis of length-frequency distributions and following the fate of marked specimens, we verified the coexistence of 5 annual cohorts and therefore a maximal longevity of more than 5 years. Possible causes of this extended life history of B. amphitrite in the study area are discussed.