This study examined the effect of a growing environmental stressor, sedimentation, on the physiology and oxidative stress throughout the different life stages of two common scleractinian corals Montastraea cavernosa and Porites astreoides. Physiology, oxidative stress, and settlement success of newly released P. astreoides larvae were measured after exposure to various turbidity treatments. No significant effects were seen on larval settlement and photosynthetic efficiency, however carbonyl content and catalase activity were significantly higher in 2015 compared to 2014; highlighting a possible inter-annual variability in susceptibility. Larval settlement deterrence in the presence of a layer of accumulated fine- or coarse-grained sediment was examined and showed significant differences between treatments but not between sediment grain sizes. Ultimately showing that any sediment can deter settlement. The deleterious effects of sediment accumulation on the survival of newly settled spat was examined by smothering with varying layers of fine- or coarse- grained sediment. Survival was significantly different by treatment with coarse-grained sediment showing decreased survival with increasing accumulation. In adult P. astreoides fragments photosynthetic efficiency significantly decreased after being exposed to layers of accumulated sediment, with recovery monitoring after exposure revealing that over time photosynthetic efficiency did not recover to pre-exposure levels. However, in M. cavernosa the photosynthetic efficiency of fragments exposed to high sedimentation saw significant recovery after exposure. Significant differences among oxidative stress biomarkers (catalase activity and carbonyl content) were seen among exposed P. astreoides fragments, however no significance was seen in M. cavernosa. Tissue mortality was also assessed with P. astreoides fragments having significantly higher mortality compared to M. cavernosa. These results highlight the negative effects of sedimentation on scleractinian corals throughout their life history stages, increasing our need for a more thorough understanding of this growing environmental stressor.

Dans de nombreux pays, l’aquaculture de pectinidés dépend aujourd’hui du succès de la production contrôlée de juvéniles. Néanmoins, les fortes variations des taux d’éclosion des oeufs et de la survie larvaire, enregistrées à ce jour, rendent cette production imprévisible. Les élevages larvaires en flux ouvert de coquilles Saint-Jacques (Pecten maximus) ont été développés en Norvège et présentent des résultats prometteurs. Malheureusement, les rendements de production encore faibles et l’impossibilité de travailler à fortes densités restent un frein majeur au développement de cette technique. En France, une technique en flux-ouvert, en petit volume (5 L), et à forte densité (≤ 300 larves mL-1) a été développée pour les ostréidés. Des expériences préliminaires visant à décliner ce système d’élevage aux larves de P. maximus se sont avérées infructueuses : retard de croissance et forte mortalité en quelques jours. Il est reconnu que les larves de pectinidés doivent faire face à des contraintes diverses en écloserie : bactériologiques, physiologiques et environnementales. Elles sont également plus sensibles que les larves des autres espèces de bivalves comme par exemple l’huître japonaise (Crassostrea gigas). Il apparait donc nécessaire aujourd’hui d’identifier plus clairement l’origine des phénomènes perturbant le bon développement des larves en flux ouvert afin d’améliorer la qualité des élevages et les rendements larvaires. Grâce à l’étude et à la compréhension des mécanismes physiologiques impliqués dans la lutte contre le stress des larves de P. maximus en flux ouvert, ce projet de doctorat donne des clés permettant d’améliorer cette technique d’élevage tout en limitant l’utilisation de produits chimiques en milieu contrôlé. / In many countries, aquaculture of pectinids depends on the success of artificial spat production in hatchery. This production is always unpredictable due to the variability of hatching rate and larval survival. Flow-through larval rearing systems were developed in Norway for the King scallop Pecten maximus and showed promising results. Unfortunately the system needs to be optimized since the larval yields and the densities used are still relatively low. In France, a small-scale (5 L) and high-density (≤ 300 larva mL-1) flow-through larval rearing system was successfully developed for oysters. First trials in such system and in similar conditions with P.maximus failed as we registered slower growth and high mortality rate in only a few days. It is known that pectinids larvae are more sensitive to environmental conditions than the oyster Crassostrea gigas, for example.Nowadays, it is important to identify and to understand the phenomena disturbing larval development in flowthrough system to improve larval quality and production yields. This doctoral project provided some indications how improving P. maximus flowthrough rearing system while limiting the use of antibiotic through a better understanding the physiological mechanisms involved in the larval response to a stressful environment