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Marine Ecology Progress Series

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MEPS 443:207-216 (2011)  -  DOI:

Growth compensation as a regulatory mechanism of purple clam Amiantis purpurata population dynamics in Patagonia

Enrique M. Morsan1,*, Paula Pappalardo2, María del Socorro Doldan1

1Instituto de Biología Marina y Pesquera Almirante Storni, Universidad Nacional del Comahue, Costanera s/n - CC 104 - (8520) San Antonio Oeste (RN), Argentina
2Estación Costera de Investigaciones Marinas and Center for Advanced Studies in Ecology and Biodiversity, Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica, Alameda 340, Casilla 114-D, Santiago, Chile

ABSTRACT: Density-dependent processes may drive the population dynamics in marine species through intraspecific competition for food or space. We examined processes controlling population dynamics in the purple clam Amiantis purpurata population of Playa Villarino (north of San Matias Gulf, Argentina) at the southernmost limits of its distribution. Population structure at this location has been dominated for more than 2 decades by 3 consecutive cohorts settled in 1978−1980. We used data on mean size and mass, growth rate, area covered by residents, density and biomass collected at 2 sites between 1982 and 2003, and a survey performed in 1995 over the whole population, to explore density dependence. The spatial pattern showed that: (1) whereas density was heterogeneous with highest values at the western side of the ground, biomass was more uniform, and the relationship between biomass and density was non-linear, becoming asymptotic at a density of 200 clams m−2; (2) body size and density decreased over time; and (3) the substrate area used by clams was less than 35% of the available substrate. Temporal patterns showed that (1) density decreased with time but biomass was almost constant, and (2) growth curves were indicative of a density-dependent effect: individuals at low-density sites grew faster than individuals at high-density sites. Differences were strong between sites and slight (or absent) between cohorts. Natural mortality, which did not differ between cohorts, was estimated by the decrease in density over time as M = 0.126. We propose that the purple clam population is regulated by a compensatory effect whereby losses due to mortality are compensated by increased growth rate, and therefore enhancement of local biomass.

KEY WORDS: Compensatory growth · Survivorship · Growth rate · Biomass trend · Amiantis purpurata

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Cite this article as: Morsan EM, Pappalardo P, Doldan MS (2011) Growth compensation as a regulatory mechanism of purple clam Amiantis purpurata population dynamics in Patagonia. Mar Ecol Prog Ser 443:207-216.

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