1. IBMP Serie Publicaciones
Regulación denso-dependiente del crecimiento individual de la almeja púrpura (Amiantis purpurata, Lamarck 1818)In this study we analyze growth, mortality and estimated biomass trend of purple clam, Amiantis purpurata, population placed in Playa Villarino, (Northern San Matias gulf, Argentina) in the southern most boundary of its geographical distribution. Previously, the population structure was described composed by three consecutive cohorts settled among 1978-1980, and the individual growth rate showed high spatial variability. The hypothesis to test in this study is that growth rate is regulated by local biomass. We choice four sites with different densities, to assess growth rate, natural mortality and retrospective estimated biomass trend. During February 2003, densities and growth rate (using external growth bands measurements) were analyzed matching with a historical time series of available data. Von Bertalanffy growth model (estimated) for each site and parameters differences between cohorts and sites were tested by likelihood ratio test. Natural mortality rate was estimated by decreasing trend of density between 1982-2003. Recruitment failure during 25 years allowed to retrocalculate historical trend of biomass in each site combining density, growth rate and mortality. Growth curves showed density-dependent effect: individuals that live in low-density sites grew faster than individuals in high density sites. Differences were significant between sites and light (or absent) between cohorts. Natural mortality rate was estimated at M= 0,126. Abundance decreased along time but biomass was almost constant. The population showed a compensatory effect between losses due to mortality with “catching-up” in growth rate, and therefore an increment of local biomass.