The venerid clam Ruditapes philippinarum is the most prominent suspension-feeding bivalve inhabiting muddy intertidal seagrass beds in Arcachon Bay (SW France). It is exploited by fishermen, and Arcachon Bay ranks number one in France in terms of production and total biomass of this species. Previous studies revealed a decrease in the standing stock of R. philippinarum since 2003 and unbalanced length-frequency distributions with a lack of juveniles and of adults > 40 mm. Consequently, the population dynamics of this bivalve were studied at four intertidal sites and one oceanic site in Arcachon Bay. As clam size structure did not allow classical dynamics computations, field monitoring was coupled with field experiments (tagging-recapture) over two years. Monitoring of condition index and gonadal maturation stages highlighted a high variability in spawning number and intensity between sites. Recruitment events in the exploited area varied spatially but with uniformly low values. Von Bertalanffy Growth Function (VBGF) parameters (K, L ∞) were determined using Appeldoorn and ELEFAN methods. In the exploited sites in the inner lagoon, K was relatively high (mean = 0.72 yr − 1) but L ∞ was low (mean = 41.1 mm) resulting in a moderate growth performance index (Φ′ = 2.99). Growth parameters were not correlated with immersion time and L ∞ was different between sites. Comparison of mortality coefficients (Z) between cage experiments and field monitoring suggested that fishing accounts for 65-75% of total adult mortality. Low recruitment, a low growth rate and a normal mortality rate led to low somatic production (4.1 and 8.7 g Shell-Free Dry Weight (SFDW) m − 2 yr − 1) and an annual P/B ratio from 0.44 to 0.92 yr − 1. Under current conditions, the possibility of a sustainable population in Arcachon Bay will strongly depend on recruitment success and fishing management.

We describe an emerging pathology, brown muscle disease (BMD), which specifically affects the Manila clam Ruditapes philippinarum in Arcachon Bay (France). BMD induces a transformation of the posterior adductor muscle, which becomes infused by conchiolin and calcified, reducing the ability of clams to bury. The disease affects both types of muscular tissue, with striated muscle becoming affected to a higher degree than smooth muscle. Two indices were created to quantify the symptoms: the Muscle Print Index, used for empty and live shells, and the Final Disease Index, utilized for live clams only. Histological sections were made and observed under light microscopy to examine the muscular damage and to investigate a causal agent. Sections revealed an important inflammatory response with a large invasion of hemocytes into tissues and a heavy necrosis of muscular fibers. Additionally, molecular biology analyses were carried out to search for bacteria and protozoan agents using generic primers. In both histological and molecular assays, bacteria and protozoans were discounted. We monitored 4 sites scattered around the bay over 2 yr. The mean prevalence was <12% without seasonal variation in 3 sites against 30% and a winter peak in 1 site. The latter site was accurately surveyed and revealed that clams at the sediment surface (abnormal position) were affected 3 times more frequently than buried clams (normal position). KEY WORDS: Brown muscle disease · Clam · Ruditapes philippinarum · Adductor muscle · Pathology · Light microscopy Resale or republication not permitted without written consent of the publisherDis Aquat Org 80: [219][220][221][222][223][224][225][226][227][228] 2008 tracal lamina and causes an obvious abnormal conchiolin deposit on the inner side of the shell, forming a characteristic brown ring (Paillard 1992, Paillard & Maes 1995a. This disease led to mass mortalities in Brittany (NW France) in 1987 and decimated stocks of cultured clams (Paillard 2004). Subsequently, BRD was observed along the French Atlantic coast and in other countries including Spain, Ireland, England, Italy and Korea (Paillard 2004, Park et al. 2006). Perkinsosis, caused by the protozoan Perkinsus sp. affects numerous molluscan species all over the world and can lead to mass mortalities (Azevedo 1989, Burreson & Ragone Calvo 1996, Goggin 1996, Da Ros et al. 1998, Park & Choi 2001, Leite et al. 2004, Cremonte et al. 2005, Villalba et al. 2005. In Korea, this parasite has been the cause of a severe decrease in clam populations since 1993 (Park & Choi 2001). Previous studies in Arcachon Bay revealed that clams could be infected by brown ring disease, perkinsosis (Lassalle et al. 2007) and also by digenean trematodes (de Montaudouin et al. 2000). However, prevalence and infection intensity were relatively low.Mortalities have been evident in Arcachon Bay in recent years, particularly during winter. A preliminary study revealed a previously undescribed necrosis of the posterior adductor muscle. Macroscopic diagnosis under...

While gradual allometric changes of shells are intrinsically driven by genotype, morphometrical shifts can also be modulated by local environmental conditions. Consequently the common use of a unique dimension (usually length) to assess bivalves’ growth may mask phenotypic differences in valve shape among populations. A morphometric exhaustive study was conducted on Manila clam,Ruditapes philippinarum, by acquiring data in the French Arcachon Bay (intrasite phenotypic variability) and by comparing with other sites in the literature (intersite phenotypic variability). 2070 shells were subsampled, weighted, and automatically measured using TNPC software. Some ratios’ values indicate a relatively round and globular shape shell in comparison with other sites confirming poor conditions for some individuals. Among adult clams, three main morphological groups were identified and discussed according to spatial considerations. Allometric relations for pairs of shell descriptors were determined by testing classical linear and piecewise regression models on log-transformed relation of Huxley. A significant shape change correlated to size was observed; it corresponds to the second year of life of the clam. Relationships between density, disease, and shell shape are demonstrated and discussed related to other potential factors affecting shell shape. Finally, consequences on population regulation are addressed.

Pathogens belonging to the genus Perkinsus infect many bivalve molluscan species around the world, including the Manila clam Ruditapes philippinarum. We investigated the spatial distribution of this parasite at 34 stations throughout Arcachon Bay (SW France). Prevalence of perkinsosis was 93% and mean infection abundance was 96 × 10 3 cells g -1 wet gill. Lowest mean abundances were found close to the Leyre River mouth and a significant negative correlation was observed between mean abundance and salinity. Perkinsosis was rare at the oceanic site where salinities and other environmental parameters were stable. A second aim of this study was to survey perkinsosis during annual cycles at 4 sites within Arcachon Bay. Prevalence and intensities (± SE) of the disease were high, on average between 70 and 100%, and 130 × 10 3 ± 6.7 × 10 3 cells g -1 wet gill. No seasonal cycle was evident. Clams were infected at 9 mm shell length and infection increased with clam size. The third objective was to determine the disinfection and infection kinetics through a 21 mo reciprocal transplantation between a nearly Perkinsus sp.-free area and a highly affected site. Disinfection appeared to be a very slow process and was similar at the site with favorable conditions for Perkinsus sp. as at the site with unfavorable conditions. Conversely, infection acquisition appeared to be episodic with spatially defined areas. Consequently, the overall lack of a clear seasonal infection pattern is interpreted as the combination of episodic infection events and slow disinfection kinetics.KEY WORDS: Ruditapes philippinarum · Perkinsus sp. · Arcachon Bay · Clam · Spatio-temporal variations · Disinfection · Infection Resale or republication not permitted without written consent of the publisherDis Aquat Org 91: [151][152][153][154][155][156][157][158][159] 2010 became naturalized, and is now a common bivalve of tidal flats along the Atlantic coast. The Manila clam has important commercial value. French production was 3000 t in 2005. Arcachon Bay (a southwestern French Atlantic lagoon) ranks first in terms of national production, with ~1000 t being produced in the bay in 2008.In Asia, Perkinsus sp. has been identified in Manila clams Ruditapes philippinarum in Korea (Choi & Park 1997, Park et al. 1999, Lee et al. 2001, Park & Choi 2001, Japan (Hamaguchi et al. 1998, Choi et al. 2002, and China (Liang et al. 2001). Perkinsus olseni is considered a severe pathogen with a highly destructive potential in clams belonging to the genus Ruditapes in Spain, Portugal and Italy (Azevedo 1989, Figueras et al. 1992, Sagristá et al. 1995, Elandalloussi et al. 2008. In Europe, Perkinsus sp. was found in R. philippinarum in Spain (Navas et al. 1992), Italy (Da Ros & Canzonier 1985, Da Ros et al. 1998 and France (Lassalle et al. 2007).Perkinsus spp. pose major threats to molluscan aquaculture around the world. Thus, it is important to determine the infection level and the dynamics of the Perkinsus sp. parasite. The present study makes a contribution by ...

To implement an ecosystem approach to fisheries management, there is a need to characterize the total pressure exerted by fisheries at the community level. French onboard observer data were used to derive catch metrics and compare fishing distribution across community components between two sites in the Southern Bay of Biscay. Sample-based rarefaction curves were used to standardize metrics across different active and passive gears, and correct for sample size differences. Six metrics for species, length and functional catch composition were tested. Length and functional metrics were found the most relevant metrics to highlight differences in catches between gears, sites, and gear-site interactions. Significant differences were found between gears, mainly in mean length and proportion of piscivores. None of the gears had the most diverse catch across all metrics. Small differences were found between sites, mainly in length range and species richness.