Phenotype plasticity, local adaptation, and biofouling influence on growth of the pearl oyster Pinctada margaritifera: A common garden approach

The purpose of our study is to investigate (1) the influence of phenotype plasticity and local adaptation on pearl-oyster physiology by testing the persistence of growth differentiation of two pearl oyster populations (Arutua and Mangareva) in common garden experiment; (2) to quantify the influence of biofouling development on the growth of each pearl oyster population. According to our observations, the growth rate in terms of total oyster weight suggested better growth performance of the pearl oyster Pinctada margaritifera in Mangareva (0.21–0.24 ± 0.01 g.day−1) than Arutua (0.14–0.15 ± 0.01 g.day−1). However, similar growth performances are observed at the Vairao common garden site for oyster stocks from Mangareva (0.07 ± 0.01 mm.day−1 or 0.15 ± 0.01 g.day−1) and Arutua (0.07 ± 0.01 mm.day−1 or 0.13 ± 0.01 g.day−1). Our results thus suggest that growth performance variability observed at the pearl farming sites of Arutua and Mangareva is due more to phenotypic plasticity than to local adaptation. This result thus accords a major importance to site selection for the pearl farming optimization process. Biofouling dynamics on Pinctada margaritifera shells differed radically between Arutua and Mangareva sites. In Arutua, biofouling colonization was relatively slow (0.016 g.oyster−1.month−1) and was mainly composed of sponges and bivalves. On Mangareva, the colonization process appeared faster and more continuous over the study period (0.15–0.18 g.oyster−1.month−1) and the biofouling community was dominated by tunicates. On the basis of our results obtained on growth performance between cleaned and uncleaned stock in Arutua and Mangareva, biofouling development after 14–15 months of colonization does not appear to have any negative effect on P. margaritifera growth. Due to the high cost of biofouling management in pearl farming facilities, our results suggest once more that reconsideration of the pearl farming management process is needed