Camille CARPENTIER

Reef effect of offshore wind farms: Impacts on primary carbon production (CARBOREEF)

The English Channel, a macro-tidal epicontinental sea, is influenced by climatic variations and subject to various anthropogenic pressures. The Norman coast is expected to become the primary wind energy producer in France by 2030. Offshore wind farms have socio- environmental impacts, both positive and negative. The structures of wind farms act as artificial reefs, creating new habitats that can increase local productivity but also lead to problems such as the introduction of non-indigenous species, habitat degradation, and modification of carbon fluxes. The lack of knowledge on these impacts is emphasized, and the precise influence of the nature of the structures on the reef effect has not yet been quantified in the English Channel, although the complexification of these artificial ecosystems seems beneficial. Projects using marine eco-engineering have shown positive results, limiting negative effects, and improving the ecological state of artificialized areas. The Interreg MARINEFF project (2019-2023) tested the contribution of eco-engineering to the biodiversity and productivity of artificialized ecosystems. The teams developed innovative materials, designs, and methodologies, evaluating eco-designed structures compared to traditional ones. BOREA's experiments focused on algae colonization and associated primary production, showing reef effect typologies ranging from so-called "primary producer" reefs rich in macroalgae to so-called "primary consumer" reefs where the functioning relies on the use of phytoplankton. In this context, an eco-design approach aims to assess the impact of different reef effect typologies on carbon primary production and its sequestration in ecosystems.

This PhD project seeks to understand and assess carbon fluxes related to primary producers in relation to the artificialization of the ecosystem due to wind farm development. The proposed experiments will be conducted both in situ and in mesocosms at the CREC-Station Marine. For the in situ approach, three pilot sites will be used to represent different zones and depths of the Courseulles-sur-Mer wind farm. The study will focus on compartments such as "macroalgae," "microphytobenthos," and "phytoplankton" to understand process modifications and their impact on primary production and potential carbon sequestration. The in situ approach will evaluate primary productivity and carbon sequestration based on different reef effect types. Eco-designed prototypes, provided by Builders - Ecole d'Ingénieurs, will be evaluated in comparison with traditional structures. Environmental monitoring of submerged structures will include the use of non-destructive methods such as photography and scraping samples. Community metabolism will be characterized using innovative benthic chambers and photosynthesis measurements based on variable fluorescence techniques. Carbon biomasses will be measured based on carbon labile properties to estimate sequestration. In parallel, experimental studies in mesocosms will be conducted on prototypes placed in mesocosms where conditions will be controlled. Three reef effect typologies will be obtained, and carbon fluxes between biological compartments will be studied with the help of 13C enrichment. Biological diversity and carbon pools will also be characterized. The complementary in situ and mesocosm approaches will help understand colonization dynamics and associated carbon fluxes during the implantation of artificial structures in the English Channel, contributing to advancing the modeling of carbon fluxes in this region.