We report the isolation, development and multiplex optimisation of 12 new microsatelliteloci for the great scallop, Pecten maximus. Diversity was moderate tohigh, with number of alleles ranging from 4 to 20 and observed heterozygosity between 0.28and 0.88. Progeny produced in a commercial hatchery was used to test locus power forparentage assignment. The percentage of offspring that was unambiguously assigned to aunique pair of parents was 97% (software package CERVUS-COLONY). Parentage assignmentrevealed that 22% of the studied progeny resulted from unplanned crosses. Effectivepopulation size of the study progeny was also estimated. Our study illustrates the powerof microsatellites for the genetic monitoring of hatchery-produced great scallops.

Sperm characteristics of scallops have not been well described in the scientificliterature. The effects of sperm release technique (thermal shock versus serotonininjection), of sperm collection technique (testis sampling versus serotonin injection), ofsperm sampling location along the genital tract, of in vitro sperm maturation, and of timepost activation on scallop sperm characteristics were assessed in the present work.Whatever sperm release technique used, no significant differences were observed regardingthe percentage of motile spermatozoa and the velocity of the average path (VAP). Comparedto testicular sperm, a higher percentage of motile spermatozoa, VAP and intracellularadenosine triphosphate (ATP) content were observed for sperm shed after serotonininjection. From the distal part of testes up to the gonopore, an increase of thepercentage of motile spermatozoa and VAP was assessed, suggesting a sperm ‘maturationprocess’ along the genital ducts. A higher increase in the percentage of motile sperm wasrecorded during a 5 min incubation of testicular sperm in seawater containing 2 mMserotonin and seawater containing 10 mM caffein compared to seawater (control). Inaddition, a higher VAP was assessed, incubating testicular sperm in caffein, compared tocontrol or serotonin. Then, the percentage of motile spermatozoa, VAP and intracellularATP content exhibited a progressive reduction during the 10 h swimming period. Mean valuesof the percentage of motile spermatozoa, VAP, sperm track linearity (LIN) andintracellular ATP content recorded at the beginning of the movement period for spermsamples collected after intragonadal serotonin injection, were 82 ± 7%,162 ± 15μm s-1, 0.33 ± 0.12 and 212 ± 133 nmol × 10-9 spermatozoa (n = 9 males), respectively. The presentstudy confirms the existence of a sperm “maturation process” along scallop genital ducts.In addition, the cessation of scallop sperm movement can be explained by the exhaustion ofATP content at the end of the movement phase.

The toxic dinoflagellate Alexandrium catenella recurrently blooms on thecoasts of France and produces Paralytic Shellfish Toxins (PSTs) that accumulate inbivalves. These toxins can affect various physiological functions including reproduction.The present study aims to validate measurements of sperm viability, DNA content andmitochondrial membrane potential in Pacific oyster Crassostrea gigasusing flow cytometry coupled with fluorescent markers, and to use thesemeasurements to assess the cellular parameters of sperm from Pacific oysters exposed toA. catenella. These parameters may influence fertilization,embryogenesis and larval development in free-spawning shellfish. Sperm viability and DNAcontent estimation were assessed using SYBR-14, which only penetrates cells with intactmembranes. Cell mortality was measured with propidium iodide (PI), which penetrates cellswith membrane damage. Mitochondrial membrane potential, used as an estimate ofmitochondrial function, was measured using JC-1 dye, which selectively enters intomitochondria and reversibly changes colour from green to orange as the membrane potentialincreases. To assess the effect of toxic algae on oyster sperm, broodstock (ripe oysters)were fed toxic (A. catenella) or non toxic (Heterocapsatriquetra) dinoflagellates at 250 cell ml-1 for 9 days. After thisexposure period, mature oysters were stripped and cellular responses of sperm analysed.Average DNA staining, as measured by SYBR-14, appeared lower and more variable in gametesfrom A. catenella-exposed oysters than in those from control oysters fedH. triquetra. Additionally, mitochondrial membrane potential of spermfrom A. catenella-exposed oysters was significantly higher (1.5 fold)than that of sperm produced by oysters fed H. triquetra. Both theincrease of mitochondrial membrane potential and the modification of DNA structure can beexpected to impact spermatozoa ability to fertilize oocytes and could thus impact relatedreproductive processes.

In the Chausey archipelago, growth of the burrowing bivalve Venus verrucosa(Mollusca: Veneridae) has been shown to be highly variable between closelylocated sites (<1 km). To explain this small-scale spatial variability, we tested thetrophic hypothesis using both fatty acid markers, and carbon and nitrogen stable isotopes(δ13C and δ15N). Environmentalparameters, including substrate, were also analysed to discriminate their effects onpotential trophic differences. Results of isotopic fractionation and lipid profiles ofwater column and digestive gland samples both showed a large contribution of phytoplanktonto the diet of V. verrucosa. More surprisingly, the same results suggestthat Phaeophyceae and Rhodophyceae macroalgae could contribute to the nutrition ofV. verrucosa as dissolved exudates. Whereas site differences were notobserved between the food sources of V. verrucosa, we showed that growthperformance index was correlated to wave height. Thus, we hypothesized that the high localgrowth variability could be controlled by the hydrosedimentary dynamics. In addition,although no significant growth differences were found between intertidal and subtidalpopulations, better condition index and more total lipids were found in the digestivegland of intertidal V. verrucosa, suggesting potential compensatorygrowth mechanisms.

The mussel (Mytilus edulis) is successfully grown in aquaculture inEurope. Mussels are usually sold live and wet storage is becoming more common. In thisstudy, oxygen demand and ammonia excretion were assessed at increasing water temperaturesand different post-harvest situations. This information was used to calculate minimal flowrates per unit biomass of live mussels sufficient to keep oxygen above 5 mg L-1or 50% saturation, and avoid accumulation of ammonia in commercial wet storage. In thisstudy, rope-grown mussels were kept out of water for 8 h to simulate harvesting conditionsand then re-immersed in holding tanks at 5, 10 and 15 °C. Oxygen and ammoniaconcentrations were measured immediately after mussels were re-immersed (0 h), after 6 hand then every day for 3 days. After this period, the mussels were again kept out of waterfor 48 h to simulate long-distance transport and once again re-immersed for the sameperiod as before. In the first 6 h after re-immersion, the oxygen consumption was between7.5 and 12.2 μmol g-1 h-1 (dry flesh) and afterthis period it decreased to a standard level of around 4.0 ± 0.9 μmolg-1 h-1 and was independent of temperature. There were no majordifferences in oxygen consumption between mussels having spent 8 and 48 h out of water atany of the subsequent water temperatures used for re-immersion. In contrast, the ammoniaexcretion showed greater differences according to temperature and time out of water.Ammonia excretion was lowest at 5 °C (<0.01 μmol g-1h-1). The implications of these results for the industry and authorities arediscussed considering the water flow rate, depuration specifications and energy costs.

Sessile animals that live on the foreshore undergo tidal cycles, and have to facevariations in physical and chemical parameters such as oxygen concentration. Duringemersion, availability of dissolved oxygen can be lowered for bivalves, which have only asmall reserve of seawater inside their closed shell. Differences in oxygen concentrationare thus expected to lead to modifications of the metabolism, including changes inmitochondrial activity. Previous studies investigated air exposure under extremeconditions, which do not always reflect environmental conditions these invertebrates haveto cope with. In this study, oxidative capacities of gill mitochondria of the oysterCrassostrea gigas were studied during a tidal cycle period, bycomparing oysters collected after emersion and immersion. Only minor differences werefound in state 3 (oxidative phosphorylation) or state 4 (non-phosphorylating oxygenconsumption) rates between the two conditions. Similarly, no difference was observed incytochrome c oxidase activity or in oxygen consumption related to maximalelectron flux through complexes I-IV, II-IV and IV. While capacities of substrateoxidation were maintained in both emersion and immersion conditions, capacity ofmitochondria to produce adenosine triphosphate (ATP) was significantly lower in oysterssampled during emersion. These results suggest that although C. gigascould maintain aerobic metabolism during emersion period within a tidal cycle inits environment, energy producing mechanisms are affected.

Bivalve molluscs survive lack of oxygen and may present cellular characteristics allowingtolerance to oxygen deprivation. The objective of the present work was to determine invitro responses of circulating cells (i.e., hemocytes) of Pacific oyster,Crassostrea gigas, to oxygen deprivation by analysis of mitochondrialmembrane potential (ΔΨm) and reactive oxygen species (ROS) production.Hemocytes submitted to oxygen deprivation showed a reduced ROS production and an increasedΔΨm. Confrontation of present results with recently reported findingsallows us to hypothesize the existence of an alternative mitochondrial reductase, and theinvolvement of mitochondrial potassium channel in maintenance of ΔΨm.Tolerance of bivalve hemocytes to variable oxygen availability appears, at leastpartially, related to mitochondrial specificities.

This study was designed to measure responses of four-year-old black-lip pearl oysters(Pinctada margaritifera) to different temperatures and foodconcentrations and to identify the energy requirements of each sex. Oysters were fed amonospecific microalgal diet of Isochrysis affinis galbana(T-iso). Measurements of oxygen consumption and ingestion rates were carried outat 24 °C and 27 °C and at two algal (T-iso) concentrations: 5000 and 30 000 cellml-1. Glycogen content in adductor muscle, absorption efficiency and scopefor growth were also estimated. Females and males responded differently to environmentalfactors, with food level being the most influential parameter. Oxygen consumption andabsorption efficiency were significantly higher in females than in males, but males hadsignificantly higher glycogen content than females. At high food concentration, glycogencontent, ingestion rate, oxygen consumption, and scope for growth were significantlyhigher than at the low food concentration. Only absorption efficiency was significantlyhigher at the low food concentration. Oxygen consumption was significantly higher at 27 °Cthan at 24 °C. These results indicate that females and males have different bioenergeticfunctioning and that energy demands for reproduction are higher in females.