The Role of Artificial Reefs in Structuring Marine Communities and Carbon Dynamics: An Experimental Approach in Mesocosms
CONTEXT AND CONTENT OF THE INTERNSHIP:
Offshore wind power is one of the main drivers of the energy transition in Europe (Karlsson et al., 2022; Zupan et al., 2023) and in France, particularly in the English Channel, which benefits from favorable climate conditions for the deployment of offshore wind farms with regular winds and relatively shallow seabed. As such, the Normandy coastline is set to become, by 2030, the leading zone for national wind power production, with several farms already active and others, such as the one at Courseulles-sur-Mer, currently being installed. However, this expansion is taking place in a coastal area already heavily impacted by various anthropogenic pressures (fishing, tourism, maritime transport, eutrophication, and coastal artificialization), generating both socio-economic challenges and significant environmental impacts. These impacts can be considered positive or negative (Raoux et al., 2018; Peña & al., 2024). The submerged parts of the wind turbine masts introduce a new hard substrate into the environment, acting as artificial reefs that can be colonized by various organisms. This phenomenon, known as the “reef effect”, increases the environment’s carrying capacity, potentially boosting local productivity and favorably influencing fisheries resources (Vivier et al., 2021). However, these artificial structures can also generate negative effects, such as the introduction of non-indigenous species, habitat degradation, or modification of carbon fluxes (Degraer et al., 2020). These fluxes are largely dependent on the activity of primary producers (macroalgae, microphytobenthos, and phytoplankton), whose photosynthetic production not only fuels trophic networks but also conditions the fixation and transfer of carbon within marine ecosystems. The deployment of artificial reefs, by influencing the abundance or composition of primary producers, could therefore modify the overall dynamics of marine carbon, with effects on the biogeochemical functioning of the areas concerned.
Since access to wind farms presents significant regulatory and technical constraints, the immersion of artificial structures on a smaller scale constitutes an interesting alternative for experimenting with and evaluating the ecological effects linked to this type of development. Artificial structures, partly composed of concrete blocks, were immersed as part of the INTERREG RECIF project (2013-2015) in the Bay of Seine and in the large harbour of Cherbourg. Previous studies have shown distinct communities and primary production for these two sites, leading to different typologies of reef effect, ranging from so-called “primary producer” reefs, rich in macroalgae, to so-called “primary consumer” reefs, where functioning is based on the use of phytoplankton (Vivier et al., 2022).
In continuation of previous work, this internship aims to study the carbon fluxes between the different biological compartments that have colonized these concrete blocks, as well as the global metabolism (photosynthesis and respiration) of these structures with an inter-site comparison. To do this, concrete blocks immersed in situ for ten years at each site will be recovered by the team of scientific divers from the MERSEA unit and the CREC, then placed in mesocosms under controlled conditions (light, temperature, oxygen, etc.).
Several methodological approaches will be implemented: 3D photogrammetry for characterizing colonized surfaces, modulated fluorescence, and deployment of O$_2$/pCO$_2$ sensors for monitoring gas exchanges. Complementary measurements of diversity, biomass, and photosynthesis will make it possible to link the community structure to their metabolic activity. Finally, a stable carbon enrichment () will be performed to trace the incorporation and transfer of carbon between producers and primary consumers using isotopic analyses. These analyses will be carried out with the support of the PLATIN’ isotope platform at the University of Caen Normandy.
This study will help to understand the dynamics of colonization and the associated carbon fluxes during the installation of artificial structures in the English Channel, contributing to the advancement of carbon flux modeling in this region.
SOUGHT PROFILE:
- Master 2 student in marine sciences, ecology, biology, or equivalent discipline.
- Skills in laboratory work, data analysis, and writing.
- Enjoyment of sea outings.
- Ability to work in a team.
- Interest in research.
APPLICATION INFORMATION
Applications (cover letter and CV) should be sent by email to Pascal Claquin and Camille Carpentier before 31/10/2025 midnight.