Effets à long terme des changements environnementaux sur la biodiversité nectonique et le fonctionnement des estuaires tropicaux – BIODIVNEK

Anthropogenic impacts are deeply modifying ? sometimes irreversibly - environments and geochemical fluxes. Estuarine and coastal ecosystems, which are among the most productive systems on Earth, are under increasing pressure due to drastic changes in land use of watersheds, acceleration of coastal urbanisation, sea rise and global warming. Among those ecosystems, tropical estuaries are marked by a high biodiversity and provide ecosystem services of high value (protein supply through fishing, water filtration, nursery habitats for juveniles) while they are severely impacted by mangrove deforestation, over fishing, aquaculture and increasing rates of sediment loading. Tropical estuarine ecosystems also yield a high diversity of habitats such as mangrove swamps, seagrasses beds, muddy or sandy sediments. These different habitats and their associated communities are not expected to respond in the same way when facing disturbances. For instance, many studies have reported seagrass loss following drastic environmental changes induced by human influence such as eutrophication. In turn, these modifications in the composition of these vegetated habitats may alter their quality for associated fish and invertebrates with, as a consequence, a loss of some ecosystem functions and a decrease in secondary productivity. In these coastal ecosystems, the nekton that is dominated by fish plays an important role in nutrient fluxes, both along the trophic level and through space with migrations. Thus, we urgently need to determine the factors (i) that maintain or threaten the biodiversity of nektonic communities, (ii) that influence fish growth, (iii) that modify fish migration patterns, and (iv) that induce shifts in trophic structures and ecosystem functioning. We focus on the Terminos tropical estuary (Mexico) coupled with the coastal Campeche Sound where historical data are available (1980, i.e. 30 years ago) on both biotic (nekton, fish) and abiotic factors (salinity, temperature, depth etc...). The Terminos lagoon, which is an exceptional case study regarding the collection of old data, is considered an archetypal tropical estuary under increasing pressure, which we can exploit to address our four issues, in particular by performing a new sampling campaign during the project to follow the dynamic since 1980. The originality of our project lies in the linking, into a single framework, of long term observations, organismal biology, and modelling. Moreover we believe that the project is innovative and original because: - Previous studies have provided a solid foundation of empirical evidence showing phase-shifts in coastal ecosystem functioning after environmental changes, yet the modelling of such relationships is still lacking in marine science. Modelling such complex systems will be very original and innovative. - We still lack large scale studies on the relationship between disturbance, ecosystem functioning and community structure. To our knowledge this will be the first time that such relationships will be investigated and modelled at large temporal and spatial scales. - The outputs from these combined analyses are likely to bring sufficient knowledge to contribute towards a better coastal ecosystem management.