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Growth of the mussel, Mytilus edulis, was compared for the first time under three culture regimes, longline located in open sea, pole and on-bottom both situated on an intertidal flat, in the Pertuis Breton, on the Atlantic coastline of France. Mussel sampling was performed on a monthly basis over 1 year while monitoring of hydrobiological parameters was conducted on a biweekly basis. Fluctuation of environmental parameters showed a similar pattern on both sea and shore locations with generally higher concentration levels for the intertidal area compared with the open sea, i.e. 4.07 and 3.17 mg l −1 for particulate organic matter, 3.16 and 2 µg l −1 for chlorophyll-a, 58.43 and 38.72 mg l −1 for inorganic-N, respectively. A clear seasonal growth pattern was observed, being similar for all three cultural conditions. A gradient of length and weight growth appeared as a function of the culture type. Longline mussels exhibited the highest performance while Bottom-type culture showed the lowest. An emersion time of approximately 26% was estimated from the temperature record of the Pole station during the period of maximal growth. This could partly explain the reduced growth in length on Pole compared to Longline. While growth was faster in Longline culture and condition index were better for Pole culture, further data on the carrying capacity of the area are needed for the establishment of a mussel culture extension policy.

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Clearance rate (CR) was measured in blue mussels Mytilus edulis L. from Aiguillon Bay and the Oosterschelde using 3 different methods: the flow-through method, the bio-deposition method and the indirect or clearance method. CR differed significantly as a function of the method used and of the origin of the mussels. CR measured with the bio-deposition method were significantly lower than rates measured with the other methods. Results for the flow-through method depended, however, on how CR was calculated. CR using the flow-through and indirect methods was on average 10.0 l g -1 h -1 in mussels from Aiguillon Bay and 5.3 l g -1 h -1 in mussels from the Oosterschelde. The significantly lower CR of mussels from Oosterschelde was related to condition index and gill area, but could not entirely be explained by these factors.KEY WORDS: Clearance rate · Intercalibration · Method · Mussels · Gill area · ConditionResale or republication not permitted without written consent of the publisher † This paper is written in memory of Serge Bougrier, who died tragically during the project.

An increasing number of hypotheses are being proposed to explain the faster growth potential of triploids in molluscs, including their partial sterility or their higher heterozygosity compared to diploids. Triploid advantage however, remains controversial for poorer sites, because of a potential trade-off with survival. These questions were addressed in Crassostrea gigas by deploying meiosis II triploids and their diploid siblings from a single mass spawning of three males and seven females, in two contrasting locations for their trophic resources. One hundred and fifty individuals were sampled at each site after nine months, measured for weight and biochemical composition, and genotyped using three microsatellite and seven allozyme loci. Higher performance was observed at the fast-growing site for all traits except shell weight, and triploids had greater weights and biochemical contents than diploids at harvest. Triploids also grew faster at the poorer site, and showed similar survival rates to diploids at both sites. Triploids had significantly higher average allozyme and microsatellite diversity. However, they performed better for a wide range of individual heterozygosity values, arguing for an advantage of the triploid state per se, that could be due to positive effects on growth of both sterility of triploids with subsequent resource re-allocation and possible faster transcription with three copies of each gene. Despite evidence of very low or no inbreeding in the diploid sample, positive associations between individual allozyme diversity and growth were detected, which explained little but significant amounts of phenotypic variation. These associations were interpreted as direct effects of allozymes, either alone or including epistatic interactions with other loci. In addition, measures of individual distance (mean-d2) specific to microsatellites, were negatively correlated with growth in diploids, indicating possible effects of outbreeding depression between more distant genomes of parents from distinct populations.