Climate change is predicted to affect the larval stages of many marine organisms. Ocean warming can reduce larval survival and hasten larval development, whereas ocean acidification can delay larval development. Ocean acidification is especially concerning for marine organisms that develop and grow calcified shells or skeletons in an environment undersaturated with calcium carbonate minerals. This study assessed the effects of ocean warming and acidification on the fertilization and larval development of the green sea urchin, Lytechinus variegatus, a tropical species common in Florida and the Caribbean. After spawning, gametes were fertilized and embryos/larvae were reared at: 1) 28°C and pH 8.1 (control), 2) 28°C and pH 7.8 (ocean acidification scenario), 3) 31°C and pH 8.1 (ocean warming scenario), and 4) 31°C and pH 7.8 (ocean warming and acidification scenario). Exposure to acidified conditions had no effect on fertilization, but delayed larval development, stunted growth and increased asymmetry. Exposure to warm conditions decreased fertilization success at a high sperm to egg ratio (1,847:1), accelerated larval development, but had no significant effect on growth. Under exposure to both stressors (ocean warming and acidification), larval development was accelerated, but larvae were smaller and more asymmetric. These results indicate that climate change will have a serious impact on the larval development and growth of the green sea urchin, L. variegatus, and may negatively affect its persistence.

For decades, humans have impacted marine ecosystems in a variety of ways including contamination by pollution, fishing, and physical destruction of habitats. Global change has, and will, lead to alterations in in a number of abiotic factors of our ocean in particular reduced oxygen saturation, salinity changes, elevated temperature (ocean warming or OW) and elevated carbon dioxide (ocean acidification or OA). Now and in the future, OA and OW will operate together with local anthropogenic drivers such as oil pollution. And yet, at present, very little is known about their potential combined interactive effects on physiological performance and tolerance of marine organisms. Therefore, multiple driver experiments are required if we are to understand and predict future vulnerability of species, populations and ecosystems. Early life stages of invertebrates are generally considered most vulnerable to environmental stress. However, few studies consider the combined effects OA and OW on survival and growth during early development of marine invertebrates, and to our knowledge, there is no information on the additional effects of oil pollution. Therefore, the aim of this thesis was to investigate the effects of combined exposure to OA, OW, and incorporating local drivers such as oil pollution on the development, morphology and physiology of three economically and ecologically important marine invertebrates. These are Northern shrimp Pandalus borealis, Northern krill Meganyctiphanes norvegica, and the green sea urchin Strongylocentrotus droebachiensis. All are cold-water species, assumed to have a narrower tolerance than more temperate species, and so could be particular sensitive to combined stressor affects. Both Northern krill and to a lesser extent Northern shrimp larvae survived experimental conditions, mirroring those predicted under a future global change scenario (combined OA and OW exposure). Neither was hatching success affected. Both shrimp and krill larvae exhibited accelerated developmental rates and incurred greater maintenance costs as a result of exposure to these stressors. Shrimp larvae showed accelerated developmental rates (-9 days), increased metabolic rates (+20 %), and increased feeding rates (+20 %), but reduced growth (- 9 %) when exposed to OW compared with the control. OA increased development rate but only at the control temperature. Although juvenile mortality of krill was not affected by predicted OA/OW conditions, metabolic rate increased significantly (+ 36 %), as did larval developmental rate, while number of moults, feeding rate and growth (- 67 %) decreased significantly (- 67 %, - 60 % and -8 % respectively). Accelerated development was accompanied by greater maintenance costs possibly due to experience a mismatch between energy supply and demand. Both species had an excess of food, and so growth reduction was more likely to be associated with higher metabolic demands in the future global change treatments. Food shortage in situ, due to variable food availability in the sea and/or mismatch with key prey species (algae and zooplankton) could result in more negative effects on growth and ultimately survival. Green sea urchins were also able to survive OA exposure, without detectable effects on hatching success. However, at day 44 post-fertilization, larval body length in the OA treatment was 9 % lower compared to the control. Furthermore, there was a significant tendency of urchin larvae to increase swimming activity in the OA conditions that might indicate compensatory feeding. Elevated maintenance and repair costs as a result of exposure to multi-stressors affected the energy budget of all the three species studied here resulting in reduced growth. Global drivers (OA and OW) resulted in trade-offs with more energy reallocated to swimming activity and metabolism, rather than growth. Exposure to oil reduced the acquisition of energy by reduced feeding which in turn resulted in less energy being available for growth. Both shrimp and sea urchin larvae showed reduced activity and feeding when exposed to oil. It is possible that the reduced swimming activity observed may be due to a narcotic effect of the oil. Furthermore, early stage sea urchin larvae showed increased mortality when exposed to oil while the older larvae did not, indicating a stage specific toxicity to oil for sea urchin larvae. The combination of global drivers and oil pollution acted additively on growth for both sea urchin and shrimp larvae. The impact of combined drivers on the size of shrimp larvae was equal the sum of the negative impacts observed for each driver: a 5 % reduction when exposed to OA and OW, a 9 % reduction when exposed to oil, and a cumulative 15 % reduction when exposed to all stressors. Similarly, the impact of combined drivers on the size of sea urchin larvae was equal to the sum of the negative impacts observed for each driver: a 14 % reduction when exposed to OA, a 9 % reduction when exposed to oil, and a 21 % reduction when exposed to all drivers. Therefore, the study demonstrated the additive physiological effects of OA, OW and a contaminant, and indicated that larval (sea urchin and shrimp) resilience to future changes (i.e. pollution) could be greatly reduced if larvae were already energy limited and severely stressed (reduced development) as a result of exposure to the global drivers. This study therefore shows the importance that the effective management of local drivers such as oil pollution could have against the backdrop of OA and OW, and emphasises that it is important to study impacts of toxicants, such as an oil pollution, in the context of predicted changes in the environment, as OW and OA are becoming major concerns. Finally, the fact that some local and global drivers seem to act additively should encourage local managers to act on local driver regulations, to obtain positive effects on local populations and environment and thereby rendering them more resilient to the negative impacts of future global drivers.

Corals face serious worldwide population declines due to global climate change in combination with direct anthropogenic impacts. Global climate change is difficult to manage locally, but policy makers can regulate the magnitude of local stressors affecting reefs. The objective of this experiment is to investigate if reducing sedimentation will enable reef corals to better endure global climate change. It has been shown that some coral species can handle climate change stress when provided with additional energy resources. Here I tested if the capacity of corals to cope with climate change can be improved when their ability to feed and photosynthesize was not compromised by increased sedimentation. Sedimentation can impede coral feeding and their ability to photosynthesize due to direct polyp blocking and increased turbidity, which reduces light availability. To evaluate the potential of enhancing coral ability to tolerate climate change by reducing a local stressor, I examined the survival and growth of brooding coral Porites astreoides juveniles when exposed to ambient and elevated water temperatures under differing sedimentation rates. I also assessed if sediment composition has significant impacts on these results. I used sediment from a reef and sediment from a boat basin within a port to mimic natural and anthropogenic sediment types and processes (e.g. dredging). Experiments were conducted to quantitatively assess the synergistic effects of sediment concentration and composition, along with increased temperature on the survival and growth of juvenile P. astreoides. The most detrimental effects were observed with anthropogenic sediment, when both sediment concentration and water temperatures were high. However, increased natural reef sediment was found to be beneficial to juvenile corals. More interestingly, I found that corals capacity to deal with higher temperatures is improved when anthropogenic sedimentation is maintained at minimal levels and turbidity resulting from sedimentation was low. Therefore, this information will aid managers in making decisions that regulate dredging and construction activities to minimize sedimentation, which will contribute to increase coral survival under climate change.

Ocean warming and acidification pose major threats to coral reef organisms. It is unknown how the early life history stages of Atlantic corals cope with the combined effects of these two global environmental stressors. Here, I investigate how these stressors influence the fertilization success, larval survivorship, and settlement of the threatened Atlantic coral, Orbicella faveolata. Gametes from O. faveolata were subjected to a factorial combination of present and future scenarios of oceanic temperatures (28.5° C and 30° C) and pH (8.2 and 8.0) predicted to occur by 2050. Results indicate that treatment type did not significantly affect fertilization success. Elevated temperature caused complete larval mortality and inhibited the settlement of O. faveolata. Interestingly, these negative effects of high temperature were partially mitigated when combined with ocean acidification. Overall, both the larval survivorship and settlement in the combined treatment was reduced to approximately half when compared to ambient treatment. Although ocean acidification may partially mitigate the negative effects of ocean warming during the larval stage, the overall reduced survival and settlement of larvae under future oceanic conditions, coupled to reduced calcification in adults, portends devastating effects on the health of this threatened species.

Dans le contexte du changement global, la diminution de la disponibilité en oxygène (hypoxie) combinée à la hausse de la température sont deux phénomènes particulièrement présents dans les eaux côtières vers lesquelles les larves de poissons peuvent dériver à la fin de leur développement. Il est admis que les régulations mises en oeuvre par les organismes pour faire face à leur environnement au cours des premières étapes de leur vie peuvent avoir des conséquences sur leur trajectoire de vie ultérieure (plasticité développementale). Ainsi, l'objectif principal de cette thèse était d’évaluer si des conditions d'oxygénation (40% et 100% de saturation) combinées à des conditions thermiques (15 et 20 °C) au stade larvaire, pouvaient avoir des impacts durables sur la physiologie des futurs juvéniles de bar (Dicentrarchus labrax). Nos résultats ont révélé que les retards de croissance associés à la plus basse température et à l’hypoxie au stade larvaire induisent une croissance compensatrice. De plus, les analyses des réserves hépatiques en glycogène et en lipides ont révélé que le métabolisme des juvéniles pourrait être affecté par les conditions environnementales au stade larvaire. Par ailleurs, nos données indiquent que la capacité d'extraction de l'oxygène a été affectée chez des juvéniles en raison de déformations operculaires causées par l’exposition précoce à l'hypoxie. Enfin, l'exposition précoce à l'hypoxie induit une sur-expression à long terme de gènes de l'hémoglobine de juvéniles replacés en situation d’hypoxie. Globalement, nos résultats contribuent à faire avancer les connaissances sur la façon dont les poissons marins font face aux changements climatiques actuels. / In the context of global change, decrease in oxygen availability (hypoxia) combined with rising water temperature are especially prevalent in coastal regions, towards which marine fish larvae may drift at the end of their development. It is well admitted that the physiological regulations implemented by organisms to cope with their environment during the early life stages of life can cause profound consequences in their subsequent life-history trajectory (developmental plasticity). Therefore, the main objective of this thesis was to investigate whether ecologically relevant conditions of oxygenation (40% and 100% air saturation) combined with thermic conditions (15 and 20 °C), occurring at the last stages of larval development of European sea bass (Dicentrarchus labrax) larvae, could have long-lasting impacts on juvenile physiology. Our data showed that growth depression resulting from low temperature and hypoxic conditions at larval stage induced a subsequent compensatory growth. Moreover, our analyses of hepatic glycogen and lipid stores revealed that metabolic features of juvenile could be affected by early exposure to oxygen and temperature conditions. Furthermore, our data revealed that oxygen extraction capacity was affected due to opercular deformities caused by early exposure to hypoxia. Finally, when seabass juveniles, that have been exposed to hypoxia at larval stage, were under chronic hypoxic condition they show a long-term up-regulation of hemoglobin genes. Overall, our findings contribute to make predictions of how the marine fish communities could be altered by current climate change.

Scleractinian corals are the ‘engineers’ of tropical coral reef ecosystems. Their three-dimensional structure provides habitat for thousands of fish and invertebrate species. The persistence of corals is threatened by climate change. In this study I investigated if corals may be able to increase tolerance to ocean warming through developmental acclimation, i.e. if corals that experience warmer temperatures during embryonic and larval development are better able to cope with higher temperatures later in life. Larvae of the broadcast spawning coral Montastraea cavernosa were raised at ambient (29°C) and future projected ocean warming temperatures (+2°C, 31°C). After larval settlement, coral juveniles from each treatment were split and reared for two months at either current or +2°C conditions. Larvae reared at the warmer temperature had lower survival and displayed a smaller size at settlement. Juveniles that were in the warmer conditions had faster growth rates. Individuals raised during larval and juvenile stages at 31°C had faster growth rates than individuals only in the elevated temperature treatment after settlement, thus indicating that developmental acclimation may have occurred. However, the highest mortality also occurred in this treatment, therefore the growth results could also be explained by positive selection of the most thermally tolerant individuals. My results suggest that acclimation and/or directed selection may help corals withstand future rises in ocean temperature.

Le plancton a un rôle crucial dans le cycle du carbone. Il est donc primordial de projeter son évolution dans le contexte de changement climatique. Une partie des résultats rapportés au niveau des communautés planctoniques montrent une stimulation de la production primaire avec l’augmentation de concentration en CO2 et très peu d’expériences combinant plusieurs facteurs ont été faites. Qui plus est, les expériences ont été réalisées majoritairement dans des conditions naturellement élevées ou enrichies en sels nutritifs et très peu de données existent dans les zones naturellement pauvres en nutriments et chlorophylle a, c’est à dire dans les zones oligotrophes telles que la mer Méditerranée, bien que ces régions représentent une surface importante et en expansion de la surface de l’océan. Plusieurs approches ont été utilisées au cours de cette thèse pour étudier les effets du réchauffement et de l’acidification de l’océan sur des communautés planctoniques dans le NO de la Méditerranée. Une des approches, restreinte à l’effet de l’acidification seule, a été l’utilisation de mesocosmes. En Baie de Calvi (expérience #1; été 2012 sur 22 jours) la communauté étudiée présentait un efficace processus de recyclage des sels nutritifs ainsi qu’une production régénérée importante alors que dans le Baie de Villefranche (expérience #2; hiver/printemps 2013 durant 11 jours) la communauté était caractérisée plutôt par un système autotrophe et par une production nouvelle dominante. Une troisième expérience a été réalisée pour étudier les effets synergétiques de l’acidification et du réchauffement de l’océan (expérience #3; March 2012; post-bloom). Toutes les expériences ont ainsi été menées dans des conditions de faibles concentrations en sels nutritifs avec des communautés dominées par des petites espèces phytoplanctoniques telles que des haptophytes, cynaobacteries et chlorophytes. Lors de l’expérience #3, toutes les populations ont décliné au cours de l’expérience (12 jours) à l’exception des cyanobactéries (principalement Synechococcus spp.) qui ont significativement augmenté durant cette période. Cette augmentation était d’autant plus prononcée dans les conditions de température plus élevée, bien que l’augmentation concomitante de CO2 ai eu tendance à limiter cet effet. Pour les trois expériences, l’acidification de l’océan seule n’a pas montré d’effet sur les taux métaboliques quelque soit la méthode utilisée (O2-LD, marquage au 18O, 13C et 14C) alors que durant l’expérience #3, les conditions élevées en température ont favorisé la production brute déterminée par la méthode de marquage 18O. Des biomarqueurs spécifiques, les acides gras des lipides polaires, utilisés de façon combinée avec du marquage au 13C a permis la détermination des productions primaires par groupe. Ceci a confirmé que l’acidification de l’océan seule n’a pas particuliérement favorisé un groupe phytoplanctonique par rapport à un autre dans nos conditions expérimentales.Basé sur nos résultats et sur une revue de littérature, il apparait que la plupart des expériences (57 % des études) réalisées jusqu’à maintenant n’ont pas montré d’influence notoire de l’acidification de l’océan seule sur les communautés planctoniques, alors que le réchauffement de l’océan semble avoir plus d’effet sur la composition et la production planctonique. De plus, la biomasse dans les écosystèmes dominés par des petites espèces de phytoplancton semble être insensible à l’augmentation de CO2. A l’heure actuelle, il est impossible, basé sur ces résultats, de fournir un concept général de l’effet de l’acidification de l’océan sur les communautés planctoniques. Cependant il semble que l’acidification n’augmentera pas la biomasse et la production primaire pour la majorité des communautés. / Plankton plays a key role in the global carbon cycle. It is therefore important to projectthe evolution of plankton community structure and function in a future high-CO2 world.Several experimental results reported at the community level have shown increased rates ofprimary production as a function of increasing pCO2 and few multi-driver experiments havebeen performed. However, the great majority of these experiments have been performedunder high natural or nutrient-enriched conditions and very few data are available in areaswith naturally low levels of nutrient and chlorophyll i.e. oligotrophic areas such as theMediterranean Sea, although they represent a large and expanding part of the ocean surface.Several approaches have been used during this thesis to investigate the effects ofocean warming and acidification on plankton communities in the NW Mediterranean Sea.One approach, restricted to the investigation of ocean acidification effects alone, was the useof mesocosms. In the Bay of Calvi (experiment #1; summer 2012 during 22 days), thecommunity was very efficient in recycling nutrients and showed important regeneratedproduction while in the Bay of Villefranche (experiment #2; winter/spring 2013 during 11days) the community was characterized by a more autotrophic state and larger newproduction. A third experiment was set-up to investigate the combined effects of oceanacidification and warming in small containers in the Bay of Villefranche (experiment #3;March 2012; post-bloom conditions).All experiments were conducted under low nutrient conditions with communitiesdominated by small species (e.g. haptophytes, cyanobacteria, chlorophytes). During the thirdexperiment, biomass of populations decreased throughout the experiment (12 days), exceptcyanobacteria (mostly Synechococcus spp.) that significantly increased during that period.This increase was even more pronounced under elevated temperature, albeit the combinationwith elevated pCO2 tended to limit this effect. For the three experiments, ocean acidificationalone had no effect on any of the metabolic processes, irrespective of the methods used (O2-LD, as well as 18O, 13C and 14C labelling) while during the multi-driver experiment #3, oceanwarming led to enhanced gross primary production as measured by the 18O labellingtechnique. Specific biomarkers, polar lipid fatty acids, were used in combination with 13Clabelling to assess group primary production rates. This confirmed that ocean acidificationalone did not favour any phytoplankton group under our experimental conditions.Based on our findings and on an extensive literature review, it appears that most (57%) of the experiments performed to date have shown no effect of ocean acidification alonewhile ocean warming seem to have an effect on plankton composition and production.Furthermore, plankton biomass in ecosystems dominated by small phytoplankton speciesappears insensitive to elevated CO2. It remains, for the moment, impossible based on thesefindings to provide a general concept on the effect of ocean acidification on planktoncommunities. However, it appears that ocean acidification will likely not lead to increasedbiomass and primary production rates for most communities, as it was previously anticipated.Furthermore, although warming will likely lead to increased primary production, it appearsthat small species with a low capacity for export will be favoured. If this proves to be awidespread response, plankton will not help mitigating atmospheric CO2 increase through anenhancement of the biological pump.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In the present work we studied the vertical profile of the Global Ocean temperature in years of occurrence El Nino-Southern Oscillation events, to better understand the functioning of this phenomenon. For its realization were used three sets of ocean reanalysis: ORAS4 produced by European Centre for Medium-range Weather Forecasts, the GODAS produced by National Centers for Environmental Prediction and SODA produced by Carton and Giese, 2008. The three sets of reanalysis showed the same potential temperature pattern in all layers of depth. The Ocean Temperature Index Equatorial Pacific is very well El Nino-Southern Oscillation events, as detected all El Niños and La Niñas occurred in the period of 52 years. Finally, it is concluded that the proposed new index can be used to determine (characterization) of El Nino-Southern Oscillation events with the same precision as the Oceanic Niño Index, and with superior accuracy for predicting El Nino-Southern Oscillation events as it detects these events several months in advance of the Oceanic Niño Index. Therefore, we can add one more tool to help us predict and better understand the El Nino-Southern Oscillation events. / No presente trabalho foi estudado o perfil vertical da temperatura do Oceano Global, em anos de ocorrência de eventos de El Niño Oscilação Sul, para compreender melhor o funcionamento deste fenômeno. Para a sua realização foram utilizados três conjuntos de reanálises oceânicas: ORAS4 produzida pelo European Centre for Medium-range Weather Forecasts, o GODAS foi desenvolvido pelo National Centers for Environmental Prediction e SODA desenvolvido por Carton e Giese, 2008. Os três conjuntos de reanálises apresentaram o mesmo padrão de temperatura potencial em todas as camadas de profundidade. O Índice de Temperatura Oceânica do Pacífico Equatorial representa muito bem os eventos de El Niño-Oscilação Sul, uma vez que detectou todos os EL Niños e La Niñas ocorridos no período de 52 anos. Por fim, conclui-se que o novo índice proposto pode ser utilizado para determinação (caracterização) de eventos de El Niño-Oscilação Sul com a mesma precisão que o Índice de Niño Oceânico, e com superior precisão para a previsão de eventos de El Niño-Oscilação Sul, uma vez que detecta estes eventos com alguns meses de antecedência em relação ao Índice de Niño Oceânico. Assim podemos acrescentar mais uma ferramenta que nos ajudará a prever e entender melhor os eventos de El Niño-Oscilação Sul.