Temperature and seston quantity and quality effects on field reproduction of farmed oysters,Crassostrea gigas, in Bourgneuf Bay, France

Abstract

-The proliferation of the voluntarily-introduced cupped oyster, Crassostrea gigas, has attained the proportions of species invasion in many intertidal habitats in Europe, presumably resulting from successful reproduction of farmed individuals. It is thus imperative to better understand the reproductive characteristics of farmed oysters, since they are directly under human control. We quantified the dry tissue mass (DTM), gametosomatic index (GSI), and reproductive cycle of farmed oysters at two sites in Bourgneuf Bay, France, in relation to environmental parameters using continuously-recording probes in 2005 and 2006. The GSI was developed for this study, based on the actual area occupied by gametes, rather than the area of the gonad previously used for quantitative histological estimation of reproductive effort. The two sites, intermediate -(IT) and high-turbidity (HT), differed markedly in the amount and quality of particulate suspended matter, and also in fine-scale temperature variations. Oysters at both sites presented two spawning periods in both 2005 and 2006; Bourgneuf Bay is thus near the northernmost European limit for a 2-spawning cycle in Crassostrea gigas. Gonad maturation was initiated when spring water temperature reached 8-10• C, and gamete atresia occurred when water temperatures transiently dipped to 15-18• C. Spawns, which occurred above 18• C, were timed by fine-scale water temperature variations. Particulate organic matter quality peaks, coinciding with gonad maturation, were related to DTM variations before spawning periods, for the IT oysters in both years, and for the HT oysters in 2006. The reproductive effort (GSI) of oysters was similar at both sites; however, the fates of the gametes differed according to site. At the first spawning, the IT oyster gamete emissions were +1 month delayed, as were peak water temperatures greater than 18• C, and more pronounced, compared to the HT site. Although the second spawning showed high proportions of atretic oocytes at both sites in both years, the IT oysters evacuated twice as many gametes as the HT oysters in 2005. The IT conditions therefore appear more suited to Crassostrea gigas gamete evacuation than the HT conditions. Key words: Reproduction / Temperature / Turbidity / Oocytes / Atresia / Biological invasion / Gametosomatic index / Bivalve / Oyster farming / Crassostrea gigas / Atlantic Ocean Résumé -La prolifération de l'huître creuse volontairement introduite, Crassostrea gigas, a atteint les proportions d'une invasion biologique au niveau de nombreux habitats intertidaux en Europe, vraisemblablement en raison du succès de la reproduction des individus cultivés. Il est donc essentiel de mieux comprendre les caractéristiques de la reproduction des huîtres qui sont cultivées. Nous avons quantifié la masse de tissus secs (DTM), l'indice gaméto-somatique (GSI) et le cycle reproducteur des huîtres cultivées sur deux sites de la baie de Bourgneuf, en relation avec les paramètres environnementaux enregistrés en continu par des sondes, e...

Shellfish Aquaculture from Space: Potential of Sentinel2 to Monitor Tide-Driven Changes in Turbidity, Chlorophyll Concentration and Oyster Physiological Response at the Scale of an Oyster Farm

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Influence of plankton concentration on gametogenesis and spawning of the black lip pearl oyster Pinctada margaritifera in Ahe atoll lagoon (Tuamotu archipelago, French polynesia)

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Evidence that rising coastal seawater temperatures increase reproductive output of the invasive gastropod Crepidula fornicata

“…Stereological methods were used to determine volume fractions of different tissue types in the histological sections (Weibel et al 1966, Briarty 1975, Morvan & Ansell 1988, Pazos et al 1996, Mayhew 2000, Beninger et al 2001. For each section of the ovary, stereological counts were performed on 3 haphazardly-chosen areas using a 10 × 10 point matrix on the microscope screen at 100 ×, as described in Dutertre et al (2009). In females, 6 tissue categories were counted: developing oocytes, mature oocytes, oocytes undergoing atresia, lysed oocytes, unoccupied tubule space, and inter-tubular space.…”

“…Normal C. gigas spawning in Bourgneuf Bay occurs from May to July (Dutertre et al 2009(Dutertre et al , 2010, so the appearance of C. fornicata larvae as early as February would permit the benthic recruitment of this species well in advance of C. gigas (which spawned in The combined effect of both an extended brooding season and increased propagule numbers may be expected to accentuate the proliferation of Crepidula fornicata in Bourgneuf Bay, and by the same token, provide a competitive advantage to this species with respect to the co-occurring Crassostrea gigas.…”