La baie de Marennes Oléron, premier site ostréicole français, est influencée par la pollution polymétallique historique de l’estuaire de la Gironde avec des concentrations en cadmium dans les huîtres proches de la limite de consommation européenne (RNO 2006; 5 μg.g-1 ps, ECNo.466/2001). Ces travaux de recherche pluridisciplinaires ont pour objectif de caractériser le comportement des ETM en zone côtière et les mécanismes de contamination en ETM des huîtres, spécifiquement en Cd, dans la baie de Marennes Oléron. Pour cela, sept missions océanographiques en période contrastée ont permis de caractériser la spéciation des ETM à l’embouchure des estuaires de la Charente et de la Gironde ainsi qu’au Pertuis de Maumusson.Une étude spatio-temporelle complémentaire des sédiments de surface de la baie de Marennes Oléron a montré un enrichissement des sédiments de surface en Cd dans la zone sud baie,confirmant la connexion des eaux girondines et l’apport en Cd particulaire à la baie par le Pertuis de Maumusson. Cette zone sud a ainsi été choisie pour mener une transplantation d’huîtres pendant trois mois. L’hydrodynamique régionale, observée par imagerie satellite, a présenté unrôle important dans la distribution et la variation temporelle des concentrations en Cd dissous et particulaires minérales de la baie. La bioaccumulation en Cd des différents organes d’huîtres cultivées sur table a été plus importante que celle des huîtres cultivées directement sur le sol,suggérant le faible rôle de la diffusion de Cd par la remise en suspension des sédiments de surface et du microphytobenthos sur la bioaccumulation. De plus, le temps d’immersion étant relativement proche entre les deux conditions, nous suggérons que la voie trophique via le plankton pélagique participe à la contamination des huîtres en plus de la voie directe. Cette contribution de la voie trophique a été confirmée lors d’expérimentations en conditions contrôlées en laboratoire par le développement d’une méthode de traçage simultané des voies de contamination directe et trophique par ajouts d’isotopes stables de Cd, conduites pour des concentrations 10 fois supérieures à l’environnement et des concentrations réalistes observées en baie de Marennes Oléron (40 ng.l-1 et ~0.7 mg.kg-1). / The Marennes-Oléron Bay, hosting the largest oyster production in France, is influenced by thehistoric polymetallic pollution of the Gironde Estuary, with cadmium levels in oysters close tothe consumption limit level (5 μg.g-1 dw, EC No.466/2001). The aim of this pluridisciplinarywork was to characterize the behaviour of trace metals in the coastal zone and the mechanisms ofCd contamination in oysters in the Marennes Oléron Bay. Seven oceanographic cruises wereconducted during contrasting season to characterize trace metals behaviour and speciation in theGironde and Charente estuaries and the coastal zone. Then, a spatial and temporal study of tracemetals in the surface sediments of the Marennes-Oléron Bay showed punctual Cd-enrichedsediments in the southern part, reflecting the connexion with the Gironde waters and theparticulate Cd inputs via the Maumusson inlet. Thus, this area was chosen to study Cdbioaccumulation in oysters over a three months transplantation. The regional hydrodynamic,observed by satellite images, played an important role on Cd speciation and the temporalvariability of dissolved and particulate Cd concentrations. Cadmium bioaccumulation in organsof oysters reared on tables at 60 cm height was more important than in oysters reared near thesediment, suggesting the absence of Cd released during tidal suspension from sediment andmicrophytobenthos. Furthermore, as the immersion time was closed between the two rearingconditions, we suggested Cd bioaccumulation via the direct pathway and also via trophicpathway of contamination by pelagic plankton ingestion. This trophic pathway of Cdcontamination was validated during laboratory experiments using a simultaneous tracing of Cddirect and trophic pathways in oysters by stable isotope spikes at concencentrations 10-foldhigher than the Gironde Estuary and at realistic concentrations observed in the Marennes-OléronBay.

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This research programme was instigated in response to concerns regarding the potential impact of sewage contamination from a long sea-outfall commissioned in 1991 in Portsmouth, Hampshire, on the long-term quality of local, historic wreck timbers. Information pertaining to the quality of seawater and the degradation of sacrificial wood samples, with particular emphasis on the action of the wood-boring crustacean, Limnoria spp, was collected and is presented in this thesis. The data was collected from three wreck sites in the Solent and surrounding waters: the Mary Rose (1509 - 1545), HMS Invincible (1744 - 1758) and HMS Hazardous (1698 - 1706). Both the Mary Rose and HMS Invincible sites are situated in an area of the Solent that was contaminated by sewage discharge. The site of HMS Hazardous is in cleaner water at Bracklesham Bay and was therefore designated as the control. Limnoriid activity was found to be higher at the HMS Invincible site than at the Mary Rose site - the HMS Invincible site also recorded the highest levels of sewage contamination. However, limnoriid activity was greater still at the "clean" control site of HMS Hazardous, thereby ruling out a conclusive link with sewage contamination. Water quality analyses showed the existence of vertical layering in the water column for many of the parameters determined. L. quadripunctata dominated the limnoriid population at the three sites but there was a significant presence of L. lignorum at the deeper Mary Rose site. On one occasion (winter 93/94), L. lignorum dominated the limnoriid population at the Mary Rose site. At the same time, the affinity for Scots pine wood observed during the rest of the study was not apparent. Faecal indicator bacteria were isolated from the biofouling layer of the wood blocks at both the Mary Rose and HMS Invincible sites and microbiological activity appeared to be greatest at the Mary Rose site. Fouling barnacles on the wood samples appeared to offer some protection from limnoriid activity in the short-term but had no long-term protective effect.

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