Body size is a fundamental structural characteristic of organisms, determining critical life history and physiological traits, and influencing population dynamics, community structure, and ecosystem function. For my dissertation, I focused on effects of body size on habitat use and diet of important coastal fish predators, as well as their influence on faunal communities in Bahamian wetlands. First, using acoustic telemetry and stable isotope analysis, I identified high variability in movement patterns and habitat use among individuals within a gray snapper (Lutjanus griseus) and schoolmaster snapper (L. apodus) population. This intrapopulation variation was not explained by body size, but by individual behavior in habitat use. Isotope values differed between individuals that moved further distances and individuals that stayed close to their home sites, suggesting movement differences were related to specific patterns of foraging behavior. Subsequently, while investigating diet of schoolmaster snapper over a two-year period using stomach content and stable isotope analyses, I also found intrapopulation diet variation, mostly explained by differences in size class, individual behavior and temporal variability. I then developed a hypothesis-testing framework examining intrapopulation niche variation between size classes using stable isotopes. This framework can serve as baseline to categorize taxonomic or functional groupings into specific niche shift scenarios, as well as to help elucidate underlying mechanisms causing niche shifts in certain size classes. Finally, I examined the effect of different-sized fish predators on epifaunal community structure in shallow seagrass beds using exclusion experiments at two spatial scales. Overall, I found that predator effects were rather weak, with predator size and spatial scale having no impact on the community. Yet, I also found some evidence of strong interactions on particular common snapper prey. As Bahamian wetlands are increasingly threatened by human activities (e.g., overexploitation, habitat degradation), an enhanced knowledge of the ecology of organisms inhabiting these systems is crucial for developing appropriate conservation and management strategies. My dissertation research contributed to this effort by providing critical information about the resource use of important Bahamian fish predators, as well as their effect on faunal seagrass communities.

Sea levels are rising due to global warming, which is induced by anthropogenic activities increasing the concentration of greenhouse gas emissions in the atmosphere. Sea level rise is already causing a severe impact on coastal wetland ecosystems, and the influence will intensify in the future. One of these coastal ecosystems is mangrove forests, which grow in intertidal zones and are therefore subject to tidal water level fluctuations. Mangrove forests provide essential ecosystem services to coastal environments and societies, and their exposure to sea level rise is a significant concern. The consequences of sea level rise, such as inundation, erosion, and lack of accommodation space, will increase the extent of mangrove loss. It is therefore essential to fully understand how sea level rise is influencing mangrove ecosystems in different geographical locations, and how likely they are to adapt and survive under different scenarios. This research used a systematic literature review to assess scientific articles from various regions, investigating the current knowledge regarding the impacts of sea level rise on mangrove ecosystems. The information was collected from 40 articles, which covered studies from five continents. The findings affirmed that the negative effects of sea level rise on mangrove ecosystems are recognized globally. It is well understood that, by the second half of the century, mangrove ecosystems will face severe issues if the highest IPCC emissions scenarios are reached. It is further well acknowledged that mangrove forests provide important ecosystem services, for example, by protecting the coastal areas under extreme weather events, benefiting natural resources sectors and recreation, and further delivering crucial climate change mitigation services by sequestering and storing blue carbon. It is therefore essential to recognize mangroves as an important ecosystem and treat them adequately. Mangrove ecosystems’ resilience under sea level rise was commonly found to be dependent on their hydro-geomorphological environment. Under sea level rise, one of the most significant factors contributing to mangroves’ survival and resilience was the availability of accommodation space, which they need to be able to migrate inland as the sea levels rise, along with their ability to adapt to changes in sediment elevation rates. To secure the needed accommodation space and to further help mangrove ecosystems grow and live under the sea level rise scenarios, adequate climate change adaptation strategies must be planned and adopted. These strategies include prioritizing high-priority areas for vegetation growth, estimating areal habitat suitability, strengthening the understanding of land use impacts on mangrove forests, and implementing hybrid solutions for coastal protection. Although the issue of sea level rise influencing mangrove ecosystems is well recognized globally, there was an observed lack of adequate research. Further research and improved understanding are needed to ensure that preparation for all emission scenarios, even for the worst ones, is possible and that climate change adaptation strategies will be well implemented.

La reconstitution des paléoenvironnements et la compréhension des dynamiques géomorphologiques sont de plus en plus appréhendées au regard des recherches archéologiques. Toutefois, en Indonésie, cette approche est encore peu usitée. L’étude du site de Kota Cina (Sumatra Nord, Indonésie) entreprise dans le cadre de cette thèse, est un travail pionnier qui vise à comprendre les changements environnementaux à l’interface Homme/Nature, dans le but d’une reconstitution paléogéographique. Cet ancien comptoir commercial portuaire du Détroit de Malacca, actif entre les XIème et XIVème siècles AD, se trouve aujourd’hui à 7 km du rivage. Afin de s’interroger sur les variables de contrôle naturelles et anthropiques de l’évolution paysagère de la région, des investigations ont été menées à Kota Cina et dans la vallée de Deli. Deux approches ont été privilégiées : (1) une approche géomorphologique qui permet de reconstituer les dynamiques hydro-sédimentaires du site et de sa vallée ; (2) une approche biogéographique à travers une analyse du contenu phytolithiques des dépôts de Kota Cina, afin de renseigner l’évolution de la végétation du site. Cette étude met en exergue des évolutions paléoenvironnementales notables, en réponse à des forçages singuliers. Le volcanisme pré-holocène de la région a engendré par son détritisme un remplissage majeur de la vallée. La réponse hydro-sédimentaire holocène a modifié la géomorphologie de la région par une forte incision et un important transfert sédimentaire. Enfin, à l’époque historique, une nouvelle transformation paysagère a eu lieu avec l’anthropisation du milieu, notamment à partir du XIXème siècle avec l’essor des plantations coloniales. / Paleoenvironment reconstructions and geomorphological dynamics understanding are increasingly being considered with regards to archaeological research. However, in Indonesia, this approach remains unusual. The present study of Kota Cina site (North Sumatra, Indonesia) is a pioneering work that aims to understand environmental changes dynamics at the human/nature interface for the purpose of paleogeographic reconstruction. Kota Cina is an ancient trade harbour of the Strait of Malacca. It was active between the XIth and the XIVth centuries AD. Nowadays, the site is located at 7 km from the coast. In order to examine the implication of natural and anthropogenic factors in the landscape changes of the region, investigations were carried out at Kota Cina and the Deli Valley. Two approaches were developed: (1) a geomorphological approach to reconstitute the hydro-sedimentary dynamics of Kota Cina site and its valley; (2) a biogeographical approach to reconstruct the vegetation changes at Kota Cina from a phytolith analysis of the site deposits. This work highlights important paleoenvironment changes as response to unique forcings. The pre-Holocene volcanism of the region generated a major filling of the valley by its detritism. The Holocene hydro-sedimentary response has altered the geomorphology of the region through a strong incision and significant sediment transfer. Finally, during the historical period, new landscape changes took place with the environment anthropisation, especially from the XIXth century with the development of colonial plantations.

Sediment accretion and elevation change in tidal forests, and the corresponding ability of these wetlands to keep pace with sea-level rise (SLR), represent data gaps in our understanding of wetland sustainability. Surface Elevation Tables and marker horizons were installed in three mature tidal forests and a restored tidal marsh, allowing us to measure elevation change, accretion, and subsidence. Additionally, we measured predictor variables to test for their significance in explaining accretion and elevation change rates. Mean accretion at our sites was 11.67 +/- 3.01 mm yr-1 and mean elevation change was -20.22 +/- 8.10 mm yr-1, suggesting subsidence occurring beneath the sites. Processes contributing to accretion and elevation change at our sites may be driven by hydrologic patterns. Comparing our elevation trends with SLR trends suggests that our study sites may not keep pace with SLR. However, we may be observing short-term oscillations that do not indicate true long-term trends.

Saltmarshes provide a diverse range of ecosystem services and are protected under a number of international designations. Nevertheless they are generally declining in extent in the United Kingdom and North West Europe. The drivers of this decline are complex and poorly understood. When considering mitigation and management for future ecosystem service provision it will be important to understand why, where, and to what extent decline is likely to occur. Few studies have attempted to forecast saltmarsh morphodynamics at a system level over decadal time scales. There is no synthesis of existing knowledge available for specific site predictions nor is there a formalised framework for individual site assessment and management. This project evaluates the extent to which machine learning model approaches (boosted regression trees, neural networks and Bayesian networks) can facilitate synthesis of information and prediction of decadal-scale morphological tendencies of saltmarshes. Importantly, data-driven predictions are independent of the assumptions underlying physically-based models, and therefore offer an additional opportunity to crossvalidate between two paradigms. Marsh margins and interiors are both considered but are treated separately since they are regarded as being sensitive to different process suites. The study therefore identifies factors likely to control morphological trajectories and develops geospatial methodologies to derive proxy measures relating to controls or processes. These metrics are developed at a high spatial density in the order of tens of metres allowing for the resolution of fine-scale behavioural differences. Conventional statistical approaches, as have been previously adopted, are applied to the dataset to assess consistency with previous findings, with some agreement being found. The data are subsequently used to train and compare three types of machine learning model. Boosted regression trees outperform the other two methods in this context. The resulting models are able to explain more than 95% of the variance in marginal changes and 91% for internal dynamics. Models are selected based on validation performance and are then queried with realistic future scenarios which represent altered input conditions that may arise as a consequence of future environmental change. Responses to these scenarios are evaluated, suggesting system sensitivity to all scenarios tested and offering a high degree of spatial detail in responses. While mechanistic interpretation of some responses is challenging, process-based justifications are offered for many of the observed behaviours, providing confidence that the results are realistic. The work demonstrates a potentially powerful alternative (and complement) to current morphodynamic models that can be applied over large areas with relative ease, compared to numerical implementations. Powerful analyses with broad scope are now available to the field of coastal geomorphology through the combination of spatial data streams and machine learning. Such methods are shown to be of great potential value in support of applied management and monitoring interventions.

Les milieux humides littoraux sont des systèmes écologiques complexes qui résultent des interactions entre des processus hydrologiques, géomorphologiques et biologiques. Ils sont généralement très convoités pour leurs intérêts tant écologiques qu’économiques. Plusieurs approches ont été employées pour mieux comprendre leurs évolutions spatiotemporelles en fonction de perturbations aussi bien naturelles qu’anthropiques qu’ils subissent. Les outils de la télédétection et des potentialités des Systèmes d’Informations Géographiques (SIG) ont été largement développés. Ainsi dans cette étude, on propose une approche cartographique de deux milieux humides, basée sur la classification orientée-objet des photographies aériennes et les images satellitaires multidates et multi-résolutions et utilisant un modèle numérique de terrain (MNT) topo-bathymétrique intégré pour étudier ces perturbations. Cette approche a permis d’étudier l’évolution de deux milieux humides situés dans deux contextes climatiques et géographiques différents qui sont l’estuaire de la Rance situé à l’ouest de la France dans un contexte tempéré océanique et ayant subi la construction d’un barrage marémoteur (aménagement hydraulique majeur) en 1966. Le deuxième milieu est le lac de l’Ichkeul situé au nord de la Tunisie, un des milieux humides les plus importants de la méditerranée qui est sujet à des aménagements hydrauliques continus et fortement dépendant des perturbations climatiques. Pour l’exemple de l’estuaire de la Rance, l’étude des évolutions géomorphologiques a été effectuée en utilisant des comparaisons du MNT intégré réalisé dans le cadre de cette étude à partir de données bathymétriques et topographiques acquises avant la construction du barrage marémoteur avec des données bathymétriques acquises en 1982 puis en 1998. On a par exemple confirmé localement les évolutions de la topo-bathymétrie. On révèle la déviation du chenal principal, ainsi que l’érosion des zones situées à l’aval à proximité du fort courant ou bien au contraire leur sédimentation dans les zones protégées de l’action des courants. L’étude de l’évolution de la végétation du schorre (herbus) a été effectuée par deux méthodes : une cartographie surfacique multidate de la végétation à partir des photographies aériennes acquises en 1953, 1961, 1966, 1978, 1982, 1996 et une orthophotographie aérienne acquise en 2002 et une cartographie de la végétation du schorre faite en exploitant les capacités de segmentation des images à haute- résolution spatiale offertes par la méthode de classification orientée-objet et le modèle topobathymétrique intégré. Cette étude comparative a montré que la surface globale du schorre a augmenté suite à la mise en place du barrage marémoteur, une tendance à l’équilibre des surfaces est observée depuis 1978. Un nouvel équilibre global s’est instauré dans l’estuaire douze ans après la construction du barrage marémoteur. Dans le cas de l’étude du milieu humide du lac Ichkeul, correspondant au deuxième exemple étudié ici, la méthode de classification orientée-objet a été utilisée pour la cartographie de l’évolution de la végétation en utilisant des images satellitaires multisources, multi-résolutions et multidates (MSS-Landsat (1972), TM-Landsat (1987), ETM+ Landsat (2001) and Aster-Terra (2007)) et le MNT topobathymétrique intégré. Cette méthode a permis d’identifier les principales communautés végétatives caractéristiques des marais de l’Ichkeul, à savoir la communauté à base de Sarcocornia fruticosa, la communauté à base d’Hordeum Marinum, la communauté à base de Visnaga Daucoides et la communauté à base de Bolboschoenus. L’évolution morphologique du lac est étudiée en comparant le MNT topo-bathymétrique intégré réalisé à partir de données topographiques et bathymétriques acquises en 2003 avec des données bathymétriques acquises en 1967, 1983, 1986 et 1993. Elle fait apparaître le déplacement des zones d’accrétion et de sédimentation dans le lac suite aux aménagements hydrauliques ainsi on relève : (1) une érosion dans la partie est du lac entre 1967 et 1982 (2) un engraissement aux alentours de l’écluse entre 1982 et 1986 et (3) un déplacement des zones les plus profondes vers le sud-ouest du lac et un comblement de la partie du lac située au pied (nord-est) du Djebel Ichkeul depuis 1993. Cette étude a montré que les modifications drastiques des apports d’eau et les perturbations climatiques constituent les principales causes des altérations physiques du milieu humide de l’Ichkeul. Le retour à une dynamique naturelle est loin d’être atteint et dépend fortement des interventions humaines et des facteurs climatiques. La méthode utilisée ici a permis d’étudier deux milieux humides différents et leurs évolutions en se basant sur le degré de complexité de chacun d’eux ainsi que sur le type de la perturbation qu’ils subissent, permettant ainsi de différencier les tendances d’évolution actuelles (stabilité ou évolution) de chaque milieu. L’étude du contexte géomorphologique associant (1) les évolutions de la végétation des milieux humides, et (2) l’exploitation de la classification orientée-objet, multidates et multi-résolutions, à partir d’une approche intégrée de télédétection utilisant les SIG présente par conséquent un fort potentiel pour proposer et optimiser les modes de gestion adaptés aux objectifs de préservation des zones humides et de développement durable en général / Coastal wetlands are an important component of the natural environment of the coastal zone. Wetlands are affected by hydrologic and geomorphic controls that must be taken into consideration when attempting to understand wetland responses to disturbance, provide information for better wetland management, or aid in the restoration of lost habitat. The functioning of coastal wetlands is a result of complex linking of distinct biological, geomorphologic and human factors interacting in varying scales. Natural water circulation and water quality can altered the natural behaviours of that ecosystem. Remote sensing techniques (pixel based classification methods) and geographic information system are well used herein in monitoring coastal wetlands areas. But they are confronted to many difficulties such as combing together both onshore and offshore data and process and discriminate wetlands from uplands areas. The overall goal of our study is to develop improved methods for wetland monitoring and management in two cases studies those are located in different areas and climate zones, which are : - The Rance estuary in Western France is subject to many morphologic and biological modifications due to the management of the Rance tidal power station since 1966. The construction had required isolating completely open sea from the Rance estuary for more three years. Since that time, some environmental changes took place in the Rance estuary area, such as modifications and disappearance of sandbanks in some areas, leading to a new equilibrium since 1978. - The Ichkeul Lake in the North of Tunisia is one of the most important wetlands in the Mediterranean region. However, the decreasing of water discharge into the lake caused by the damming of three of the six major rivers feeding the lake coincided with severe drought periods, restricting supplies of fresh water, and modifying saltmarsh vegetation communities and other significant wetland degradation. Furthermore, one specific objective of our work is to investigate the capabilities of the object oriented classification methods combined to integrated topographic-bathymetric digital terrain model in those areas. In the case study of the Rance estuary morphological evolution after the settlement of the tidal power station is done by the comparison of the integrated Topographic-Bathymetric Digital Terrain Model (DTM), combining the 1953 bathymetric data, and 1957 topographic ones, with bathymetric profiles acquired in 1982 and 1998. It shows that increase of topography corresponding to accretion is frequently observed in coves characterised by low current energy. In contrast, the places exposed to high currents present generally strong eroded features, which decrease and erode the topography. The meandering of channels has also observed through time. The use of object-oriented classification of aerial photographs, acquired between 1953 and 2002 and the integrated DTM of salt marshes area in the Rance estuary, enhanced their surface regression from 1953 to 1978. It shows their stability since, due to hydrologic modifications induced in the Rance estuary after the tidal power plant management such us the change of tidal range and the period of slack water. In the case study of the Ichkeul, the application of object-oriented classification approach to identify Ichkeul wetland vegetation is based on the following multi-spectral imagery: the MSSLandsat (1972), TM-Landsat (1987), ETM+ Landsat (2001) and Aster-Terra (2007) acquired in growth period of vegetation. Results show the declining of vegetation communities in Ichkeul wetlands exposed to alternative fresh and salt-water diversion. Sarcocornia fruticosa, communities, Hordeum communities are the largest units in the study area. The Bolboschoenus communities is absent in the 1987 and 2001 vegetation maps. This is conformed by previews studies witch are showing that due to dry periods and rivers damming the Bolboschoenus disappeared for many years. The monitoring the lake Ichkuel sedimentation process was done by comparison of five sets of bathymetric data taken in 1967, 1983, 1986, 1993 and 2003. It shows the alteration of sedimentation process in the Ichkeul Lake as behaviour of the coastal zone after the settlement of dams. To conclude, owing to difference of climatic and hydrodynamic characteristics the responses of coastal wetland to natural and human will vary according to difference of their geomorphology and ecology. The Rance estuary seams to have new ecology balance ten years after the settlement of the tidal power station. However, the Ichkeul Lake is still affected by anthropogenic and climatic factors. Therefore, the used methodology provides detailed information on wetland vegetation and adjacent land-use/land-cover types in schorre wetland areas in the cases of the Rance estuary, and the Ichkeul marches areas. This technique is combining both integrated DTM and remote sensing data that is a useful tool for wetland vegetation monitoring and for resolve some major classification confusions that occur in such wetland areas

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