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Asari (=Manila) clam, Ruditapes philippinarum , is the second bivalve mollusc in terms of production in the world and, in many coastal areas, can beget important socio-economic issues. In Europe, this species was introduced after 1973. In Arcachon Bay, after a decade of aquaculture attempt, Asari clam rapidly constituted neo-naturalized population which is now fished. However, recent studies emphasized the decline of population and individual performances. In the framework of a national project (REPAMEP), some elements of fitness, stressors and responses in Arcachon Bay were measured and compared to international data (41 publications, 9 countries). The condition index (CI = flesh weight/shell weight) was the lowest among all compared sites. Variation in average Chl a concentration explained 30% of variation of CI among different areas. Among potential diseases, perkinsosis was particularly prevalent in Arcachon Bay, with high abundance, and Asari clams underwent Brown Muscle Disease, a pathology strictly restricted to this lagoon. Overall element contamination was relatively low, although arsenic, cobalt, nickel and chromium displayed higher values than in other ecosystems where Asari clam is exploited. Finally, total hemocyte count (THC) of Asari clam in Arcachon Bay, related to the immune system activity, exhibited values that were also under what is generally observed elsewhere. In conclusion, this study, with all reserves due to heterogeneity of available data, suggest that the particularly low fitness of Asari clam in Arcachon Bay is due to poor trophic condition, high prevalence and intensity of a disease (perkinsosis), moderate inorganic contamination, and poor efficiency of the immune system. [ABSTRACT FROM AUTHOR]

Recently, Manila clam, Ruditapes philippinarum, populations have suffered mortalities in Arcachon Bay (SW France). Mortality was associated with extensive lesions of the posterior adductor muscle, which become progressively brown and calcified. Ultrastructural observations by transmission electron microscopy revealed tissue degradation with necrotized muscle fibres and granulocytomas. Unenveloped virus-like particles (VLPs) were detected in muscle, granulocytic, epithelial and rectal cells. VLPs were abundant in the extracellular space, in the cytoplasm (free or enclosed in vesicles) and in the nucleoplasm of granulocytes. Nuclei and mitochondria of granulocytes displayed changes which suggested reactive oxygen species production and apoptosis induction. VLPs exhibited an icosahedral structure with a diameter of 25 to 35 nm. These observations suggest that the VLPs could belong to the family Picornaviridae or the Parvoviridae. [ABSTRACT FROM AUTHOR]

The Manila clam Ruditapes philippinarum (Adams and Reeve, 1850) is one of the mollusc species that, driven mainly by the shellfish market industry, has extended throughout the world, far beyond the limits of its original habitat. The Manila clam was introduced into France for aquaculture purposes, between 1972 and 1975. In France, this venerid culture became increasingly widespread and, since 1988, this species has colonised most of the embayments along the French Atlantic coast. In 2004, this development resulted in a fishery of ca. 520t in Arcachon Bay. Within this context, evaluation of the clam stock in Arcachon, as undertaken by the French Institute for the Marine Research (IFREMER) in 2000, 2003 and 2006, underlined: (a) the presence of disequilibrium in the population structure and (b) the need for an improved knowledge of the population dynamics. In order to meet these requirements, a research project was initiated. The main objective of this study was to provide an improved knowledge of the biotic and abiotic parameters which control the dynamics of the clam population, within Arcachon Bay (growth, mortality, reproduction, trophic sources, etc.). With these data, the aim of the present study is to develop a system dynamics model, capable of predicting clam population evolution within the embayment, in response to different management measures. Once the model was constructed, the effect of diverse management measures and environmental scenarios on the stock response, over time, was simulated: (i) sensitivity to exceptional environmental changes (sea water temperature); (ii) changes in the minimum legal size for capture; (iii) changes in season capture duration; (iv) an increase of the surface area of no-take zones. Considering all the assumptions made here, the best management decisions are those which are able to maximise, at the same time, the captures and the number of shellfishers; likewise, minimise stock losses, as a consequence of this exploitation. Taking into account this approach, the best management decisions are, in order of efficiency: (i) the minimum legal size for capture maintenance; (ii) a reduction in the capture season; (iii) an increase of no-fishing zones. [Copyright &y& Elsevier]