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Strategies for biomass control are actively sought in response to proliferation of the introduced, suspension-feeding gastropod Crepidula fornicata along European coasts. Among these, dredging, crushing and on-site rejection may only be envisaged if the risk of further dissemination through the release of gametes and of excapsulated embryos/larvae is found to be nil or extremely low. This study evaluates such risk using three approaches: (1) determination of the periods of brood presence/absence, (2) external fertilizations of gametes obtained by gonad stripping, (3) cultures of mechanically-excapsulated embryos and larvae. A period of near- or total brood absence was observed between September 2006 and January 2007. The few zygotes (1.5% to 7.5%) obtained from external fertilizations did not proceed beyond the 4-cell stage. Excapsulated young embryos and mid-stages died in less than 4 days of culture. Despite their ability to swim, grow and feed, excapsulated veligers all died before metamorphosis. No juveniles were obtained from external fertilizations and excapsulated cultures, indicating that the release of crushed catches directly at sea could not present a dissemination risk from the standpoint of gamete or prematurely-excapsulated larval dispersal. Furthermore, by carrying out the crushing operations during the period of brood absence, the dissemination risk becomes nil. Negative ecological impact of such operations could be offset by attraction of motile predators, as yet unaccustomed to this introduced species, and their subsequent generalization to live slipper limpets and invasive feral Crassostrea gigas. At the very least, this biomass reduction approach would concentrate bottom habitat unavailability to restricted zones, freeing up the rest of the subtidal for other, formerly displaced species, as well as reducing the pressure on the trophic carrying capacity of affected habitats. La prolif?ration des cr?pidules, Crepidula fornicata gast?ropode suspensivore, le long du littoral europ?en, a stimul? de nombreuses strat?gies de contr?le de sa biomasse. Parmi elles, le dragage, broyage et relargage sur site des cr?pidules sont envisageables ? condition que le risque de diss?mination additionnel, li? au rejet de gam?tes et/ou d''embryons/larves excapsul?s, soit nul ou extr?mement faible. Trois ?tudes sont effectu?es pour ?valuer ce risque?: (1) la d?termination des p?riodes de pr?sence/absence de pontes, (2) les f?condations externes de gam?tes obtenus par scarification des gonades, (3) les cultures d''embryons et de larves m?caniquement excapsul?s. Une p?riode d''absence totale de ponte est observ?e entre novembre 2006 et janvier 2007. Les quelques zygotes obtenus (de 1,5?% ? 7,5?%) ? partir des f?condations externes ne survivent pas au-del? du stade 4 cellules. Les jeunes embryons et les stades interm?diaires excapsul?s sont morts en moins de quatre jours de culture. Malgr? leur capacit? ? nager, cro?tre et se nourrir, toutes les larves v?lig?res excapsul?es sont mortes avant la m?tamorphose. Aucun juv?nile n''a donc ?t? obtenu ? partir des f?condations externes et des cultures de propagules excapsul?es, indiquant que le relargage de cr?pidules broy?es en mer pr?senterait peu de risques de diss?mination par les gam?tes et par les larves pr?matur?ment excapsul?es ? partir du site de rejet. De plus, en effectuant les op?rations de broyage hors des p?riodes de ponte, le risque de diss?mination serait extr?mement faible. Les impacts ?cologiques n?gatifs g?n?r?s par de telles op?rations pourraient ?tre compens?s par l''attraction de pr?dateurs, encore non accoutum?s ? cette esp?ce introduite, sur les sites de rejet, pouvant stimuler leur pr?dation par l''abondance de cr?pidules vivantes et d''hu?tres sauvages Crassostrea gigas. De plus, le rejet de broyats pourrait ?tre concentr? sur des zones d?limit?es, permettant ainsi de lib?rer des habitats, du reste de la zone subtidale, pour d''autres esp?ces autrefois d?plac?es et de r?duire la pression trophique exerc?e par la cr?pidule sur les habitats infest?s. [ABSTRACT FROM AUTHOR]

Understanding the quality cues which govern the grazing of phytoplankton by suspension feeders is essential to understanding seston dynamics and benthic–pelagic coupling. We studied the effect of functioning cellular status on selection of two common coastal diatoms, Coscinodiscus perforatus var. pavillardii and Actinoptychus senarius, grazed upon by the commercially farmed oyster, Crassostrea gigas Thunberg. Two contexts were investigated, corresponding to those naturally encountered by oysters and their prey: (i) diatoms (C. perforatus var. pavillardii) larger than the size allowing selection on the gill (hence subject to selection on the labial palps only) and (ii) diatoms (A. senarius) within the size range allowing selection on the gill (hence subject to selection on both the gills and labial palps). Both intact and naturally dead cells possessed a perifrustular envelope, but the naturally dead cells lacked intracellular organic content. Oysters were able to discriminate between intact and naturally dead (empty) cells, both in the absence of prior selection on the gill and subsequent to prior selection on the gill. In contrast to previous findings in scallops, functioning cellular status is thus an important determinant of diatom selection and ingestion by oysters. This fine degree of discrimination may have evolved as an adaptation to the high turbidity, low food-quality estuarine environment typically colonized by oysters. The reduced organic content of rejected diatom cells in oyster pseudofaeces may affect the organic content of biodeposits, and subsequently the dynamics of nutrient release to the water column during mixing and resuspension. [ABSTRACT FROM AUTHOR]