• Energy Research

Les effets actuels du changement climatique dû aux émissions de gaz à effets de serre, sur les écosystèmes et les sociétés sont indéniables. La France dispose de nombreux gisements lui permettant de développer les Energies Marines Renouvelables, et notamment les parcs éoliens, afin d’opérer une transition énergétique. L’objectif de cette thèse est de mettre en place une approche écosystémique estimant les effets combinés de l’implantation d’un parc éolien flottant dans le Golfe de Gascogne et du changement climatique. Premièrement, un modèle de distribution spatiale des espèces a servi à projeter la niche écologique potentielle des espèces de poissons et de céphalopodes du Golfe de Gascogne, ainsi que des espèces subtropicales non indigènes, indiquant une modification des communautés marines. Puis, plusieurs modèles Ecopath ont été mis en place pour projeter les conséquences de ces arrivées sur le réseau trophique actuel, illustrant de nombreux impacts. Enfin, une spatialisation de ces deux premières parties a été réalisée grâce au module Ecospace, pour simuler l’implantation d’un parc éolien flottant, avec ses effets sur la faune marine (i.e. effet récif, effet DCP et effet réserve), dans un écosystème déjà soumis au changement climatique. Les résultats indiquent des effets positifs sur la faune marine à l’intérieur du parc. The current effects of climate change due to greenhouse gas emissions on ecosystems and societies are undeniable. France has many deposits which permit to develop Renewable Marine Energies, and in particular wind farms, in order to proceed an energy transition. The objective of this thesis is to set up an ecosystem-based approach estimating the combined effects of two pressures: the installation of a floating wind farm in the Bay of Biscay and the climate change. First, a species distribution model was used to project the potential ecological niche of fish and cephalopod species in the Bay of Biscay, as well as non indigenous subtropical species, showing a modification of marine communities. Then, several Ecopath models were set up to project the consequences of these arrivals on the current trophic network, illustrating the deep modifications. Finally, a spatialization of these first two parts was carried out using the Ecospace module, to simulate the installation of a floating wind farm, with its effects on marine fauna (i.e. reef effect, FAD effect and reserve effect), in an ecosystem already submitted to climate change. The results indicate positive effects on marine fauna within the park

The consequences of climate change for marine organisms are now well-known, and include metabolism and behavior modification, distribution area shifts and changes in the community. In the Bay of Biscay, the potential environmental niches of subtropical non-indigenous species (NIS) are projected to expand as a response to sea temperature rise by the mid-century under the RCP8.5 climate change scenario. In this context, this study aims to project the combined effects of changes in indigenous species distribution and metabolism and NIS arrivals on the functioning of the Bay of Biscay trophic network. To do this, we created six different Ecopath food web models: a “current situation” trophic model (2007–2016) and five “future” trophic models. The latter five models included various NIS biomass combinations to reflect different potential scenarios of NIS arrivals. For each model, eight Ecological Network Analysis (ENA) indices were calculated, describing the properties of the food web resulting from the sum of interactions between organisms. Our results illustrate that rising temperature increases the quantity of energy passing through the system due to increased productivity. A decrease in the biomass of some trophic groups due to the reduction of their potential environmental niches also leads to changes in the structure of the trophic network. The arrival of NIS is projected to change the fate of organic matter within the ecosystem, with higher cycling, relative ascendency, and a chain-like food web. It could also cause new trophic interactions that could lead to competition and thus modify the food-web structure, with lower omnivory and higher detritivory. The combined impacts (increasing temperatures and NIS arrivals) could lower the resilience and resistance of the system.

Under climate change, future species assemblages will be driven by the movements and poleward shift of local species and the arrival of more thermophilic species from lower latitudes. To evaluate the impacts of climate change on marine communities in the Bay of Biscay, we used the hierarchical filters modelling approach. Models integrated 3 vertical depth layers and considered 2 Intergovernmental Panel on Climate Change (IPCC) scenarios (Representative Concentration Pathway, RCP2.6 and RCP8.5) and 2 periods (2041-2050 and 2091-2100) to simulate potential future species distributions. Results predicted potentially suitable future ranges for 163 species as well as future arrivals of non-indigenous southern species. We aggregated these results to map changes in species assemblages. Results revealed that coastal areas would undergo the highest species loss among the Bay of Biscay species, depending on their vertical habitat (benthic, demersal, benthopelagic or pelagic). Benthic and demersal species were projected to experience a westward shift, which would induce a deepening of those species. In contrast, pelagic species were projected to shift northward. The potential ecological niche for half of the studied species, mostly benthic and demersal, was projected to decrease under climate change. In addition, a high rate of southern species arrivals is expected (+28%). Assessment of community composition showed high species replacement within the 0-50 m isobath, driven by the replacement of native species by southern ones. This could lead to a major reorganization of trophic networks and have socio-economic impacts.