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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.

Spatial and temporal scales of variability in phyto-and bacterioplankton abundance were investigated in a deep atoll lagoon (Ahe, French Polynesia). Ahe Lagoon showed a classical phytoplankton composition, but its picophytoplankton (Prochlorococcus, Synechococcus and picoeukaryotes) concentrations are higher than the mean for Polynesian atoll lagoons. Phyto-and bacterioplankton descriptors were highly variable, with mean CVs of > 20% in most cases: daynight, day-to-day, vertical, lagoonal and seasonal. Phytoplankton biomass, which was estimated by in vivo fluorescence, was higher in the deep layer than in the upper layer. This pattern was detected on a day-night scale, showing transitory vertical gradients, and through long-term events that were recorded during day-to-day measurements, especially during low wind conditions. The main factors potentially driving this vertical structure of the phytoplankton appeared to be photoinhibition in upper layers and a bottom effect providing more favourable nutrient conditions in deeper layers. Day-to-day fluctuation was the major source of temporal variation and appeared to be highly driven by vertical patterns and mixing events showing phytoplankton supply from deep layers. At the lagoon scale, the picophytoplankton exhibited a patchy structure that is closely linked to the geomorphology of the rim, lagoon depth and proximity of the pass. Stations close to the pass were characterized by consistently lower Synechococcus and picoeukaryote concentrations. Lastly, warm periods showed higher Synechococcus, nanophytoplankton and bacterial concentrations. Prochlorococcus and picoeukaryotes showed no seasonal trend, but had an annual variability that could be related to variations in exchanges between the lagoon and the ocean.KEY WORDS: Flow cytometry · Picophytoplankton · Nanophytoplankton · Bacterioplankton · Vertical distribution · Day-to-day dynamics · Large-scale heterogeneity · Deep atoll lagoon · French Polynesia Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 59: [89][90][91][92][93][94][95][96][97][98][99][100][101] 2010 Microbes play major roles in pelagic food webs and biogeochemical cycles (Pomeroy 1974, Cho & Azam 1990. They respond quickly to temporal and spatial variations in their environment; the scale and source of such variability are likely to play a significant role in the long-term equilibrium of an ecosystem (Haury et al. 1978, González et al. 1998. Therefore, despite the environmental homogeneity commonly assumed in atoll lagoon waters, numerous studies highlight transitory variations in hydrobiological parameters at small scales, such as in day-to-day, diel or vertical distributions of temperature, salinity, chl a or microbial community abundance (Sournia & Ricard 1976, Moriarty et al. 1985, Charpy-Roubaud et al. 1988, Charpy & Blanchot 1998, González et al. 1998, Buestel & Pouvreau 2000. However, most of these studies were done in shallow lagoons, which were usually considered as well mixed and...

Several experiments using a self-regulated system were conducted to define the factors likely to influence the uptake of paralytic shellfish poison (PSP) by oysters in the Penzé estuary (France, Brittany). Each 4-day experiment was carried out in a recirculated sea water system using 15 Pacific oysters (Crassostrea gigas) separated from each other and supplied with unfiltered natural seawater containing alternatively toxic (Alexandrium minutum) or non-toxic (Skeletonema costatum) algal diets. The food supply and exposure times to toxic diets were determined according to field studies of the upstream and downstream movement of patches containing A. minutum. The experimental parameters corresponded roughly to the hydrological conditions generally observed in June when tidal coefficients are lowest and blooms occur: (i) A. minutum concentrations in sea water of 200, 5000 and 10 000 cell ml −1 ; (ii) inorganic matter consisting of 5 and 15 mg L −1 of calcinated muddy sediments; and (iii) low and high tide salinities of 25 and 35% , respectively. Significant experimental contamination (greater than the 80 µg STX equiv. 100 g −1 sanitary threshold) occurred after 4 days of exposure for the monospecific A. minutum diet (20−200 cell ml −1) and alternated A. minutum and S. costatum diets (5000 and 20 000 cell ml −1 , respectively). Contamination levels were less than the sanitary threshold for alternated A. minutum/S. costatum diets of 200 and 20 000 cell ml −1 , respectively, and for a monospecific A. minutum diet (1000−10 000 cell ml −1). In the last case, the accumulation rate was quite low, possibly because of inhibition of the filtration rate related to a lower biodeposit production rate and decreased feeding time activity. The addition of inorganic matter appeared to play a significant role in the observed increase of toxin uptake, whereas salinity was not a determining factor for toxin accumulation rates. These last observations were corroborated by statistical analysis and stepwise multiple linear regressions integrating all or some of the experimental parameters.