France CLIMAREST – Resilient Ecosystems for Resilient Communities Upscaling Native Oyster Restoration and Evaluation of Ecosystem Services

Leading partners : SEABOOST, Ifremer

Collaborating institutions : Comité régional de la conchyliculture de Bretagne Sud, Cochet environnement, Syndicat ostréicole de la baie de Quiberon, OFB, Syndicat mixte de gestion du grand site dunaire Gâvres Quiberon, Auray Quiberon Terre Atlantique.

Co-funding from the European commission as part of Horizon Europe and EU Mission “Restore our Ocean and Waters by 2030”

Oyster restoration activities of the CLIMAREST project build on past research in France and Europe and focus on developing new knowledge and tools for upscaling and promotion of native oyster restoration projects as nature-based solutions for resilient coastlines and coastal communities.

Recent projects have proven essential in defining the conditions in which the species could be restored in the regional context of Brittany in France. However, restoration trials undertaken within these projects have been developed at a limited scale (m²) and have mostly focused at comparing the performance of different substrates for restoration. Upscaling the restoration of this species and its associated habitat now requires the development of scalable processes (focus: how we do it?) and a better quantification of associated ecosystem services to engage a wider set of stakeholders in future restoration efforts (focus: who does it and why?).

CLIMAREST actions and objectives are defined in collaboration with and as complement to the REEFOREST research project, supported by Ifremer and the French Office of Biodiversity.

In this context, the first objective of the project is to develop and test restoration protocols applicable at the hectare scale. Demonstration trials are carried out in two contrasting sites in which France’s main remaining flat oyster populations can currently be found: Rade de Brest and Quiberon Bay. Work on these two historical pilot sites benefits from the availability of extensive baseline data, and from collaboration with the French Office for Biodiversity. Work on these two sites also allows to account for different ecological sensitivity, varying human activity and stakeholder engagement, therefore leading to customized restoration methods and roadmaps.

Based on previous tests, specific substrate designs were developed and deployed in June/July 2023 and June/July 2024, at the peak of larval concentration. These structures are monitored over the course of the project to evaluate their effectiveness for restoration of large-scale oyster aggregates and will be used in comparison to adjacent control sites representative of the general state of the remaining oyster populations dispersed on the seabed. Substrates and structures used in the various trials include steel, rope made of natural fibers and an innovative hard substrate composed only of particles of crushed shells bound together using a biocalcification process.

*Quiberon Bay restoration site.*
Photo: Nicolas Brikke

*Ireef formation on settlement dome at T+1 year.*
Photo: Sébastien Petton, Ifremer

In Quiberon Bay, the potential of oyster restoration as a tool for erosion mitigation is evaluated through specific modeling work and in situ instrumentation. A physics-based numerical model was setup to appreciate the potential influence of different restoration scenarios on various aspects of local hydro-sedimentary dynamics. First results show that restored roughness of the seabed could have a significant influence on wave- and tide- induced hydrodynamics of the adjacent shoreline and could contribute to reduce beach erosion. Oyster reefs were also instrumented to develop specific values for current and wave friction coefficients.

In the bay of Brest, the filtration services provided by different restoration scenarios were assessed using a theoretical approach coupling clearance rate data to hydrodynamic modelling. First results strongly suggest that oyster populations associated to large-scale restoration efforts would have a relatively important effect on the suspended matter and phytoplankton loads in the bay and could lead to a significant improvement of water quality. To refine the study of this essential filtration service provided by flat oyster reef formations, an experimental in vivo approach is planned from summer 2024. The principle is to measure filtration in situ in a population of restored oysters of known density.

CLIMAREST will contribute to a better understanding of carbon storage potential of native oyster reefs in underlying sediments through the study of sediment and bio-deposition stabilization processes. Blue carbon is identified as a possible funding source for oyster restoration in some specific cases, and the extent of carbon storage for this species and habitat requires further demonstration and quantification. These models are supported by in situ data collected through specific campaigns and experiments (sediment coring and carbon analysis, sediment elevation evaluation, effect of oyster aggregate rugosity on water flow, water clearance rates…).

Last but not least, the project investigates the biodiversity associated to oyster reefs and focuses more specifically on two aspects: epiotic communities associated to the flat oyster according to the state of development of the reef, and interactions with surrounding habitats. One of the objectives of this work is to define specific biodiversity indicators and values that may serve in the evaluation of the success of restoration from the perspective of a reference state of conservation.

All data produced within the CLIMAREST project will be made available at the end of the project end of 2025.From a stakeholder engagement perspective, the project is contributing to develop an upscaling roadmap for Quiberon Bay, in collaboration with the area’s main public institutions and with representatives of the oyster farming industry. CLIMAREST also provides support to the development of alternative civil society-based restoration initiatives.

More infos on project here: https://climarest.eu