The dual climate role of seagrass meadows in Arcachon Bay

2026

Article référencé dans le Web of Science WOS:001695954000001

Dolivet-Maréchal M., Schmidt S., Cognat M., Schübert C., Gervaix J., des Chatelliers C. C., Labourdette N., Bertrand I., Rossi L. M., Dugué Rémi, Ahr M., Richaume A., Le Roux X., Florio A.

Earth Systems and Environment, 2026, [Early access], p. [17 p.] ISSN 2509-9426

Vegetated coastal ecosystems such as seagrass meadows are increasingly recognized as key contributors to climate regulation. Acting as blue carbon sinks, they exhibit carbon burial rates up to 30-50 times higher than those of terrestrial forest soils, thereby storing large amounts of organic carbon in their sediments. However, these benefits may be partly offset by the release of greenhouse gases (GHG), particularly methane (CH4) and nitrous oxide (N2O), which possess a much higher global warming potential than CO2. Comparing seagrass meadows to bare sediments helps identify their specific role as blue carbon ecosystems. In this study, we assessed carbon accumulation rates (CAR) together with in situ fluxes of CH4 and N2O in Zostera noltii seagrass meadows and adjacent bare sediments within Arcachon Bay, France, which hosts Europe's largest Z. noltii meadows. Our results demonstrate that seagrass areas exhibit CAR values that are 2.5 times higher, highlighting their superior carbon burial capacity. However, GHG emissions from seagrass meadows were 3.5 times higher than those from bare sediments, offsetting 28.7 +/- 0.3% of the estimated net climate benefit provided by carbon burial across the bay. Hydrodynamic conditions influence this balance: sheltered areas promote organic matter accumulation but also amplify GHG emissions. Despite these trade-offs, Z. noltii meadows still provide a net climate benefit 2.2 times greater than bare sediments, emphasizing their significant contribution to climate regulation. These findings highlight the dual nature of seagrass meadows as both carbon sinks and GHG sources. Incorporating GHG flux estimates into blue carbon assessments will improve global model predictions and guide better conservation and restoration strategies.Graphical AbstractThis graphical abstract provides a concise and visually engaging summary of the study assessing the net climate benefits of seagrass meadows in Arcachon Bay, France. The comparison between seagrass meadows with adjacent bare sediments at seven study sites with six replicates for each sediment type, highlighting the dual processes of carbon burial and greenhouse gas (GHG) fluxes (CH4 and N2O). Downward green arrows represent the burial of organic carbon in sediments, while upward red arrows illustrate gaseous emissions to the atmosphere. The balance between these opposing fluxes is central to understanding the overall climate impact of coastal ecosystems. The bar plots emphasizes that, although seagrass meadows bury carbon at rates 2.5 times higher than bare sediments, they also release 3.5 times more GHG, offsetting part of their climate benefit. Importantly, the net climate contribution of seagrass meadows remains 2.2 times greater than that of bare sediments. By distilling the study into a clear and intuitive image, this graphical abstract provides readers with a rapid understanding of the research without reading the full manuscript. It underscores the importance of integrating both carbon burial and GHG fluxes into blue carbon assessments and highlights the value of conserving and restoring seagrass meadows to mitigate climate change, providing actionable insights for their restoration and management.

Sciences du milieu [021] ; Ecologie, systèmes aquatiques [036] ; Etudes, transformation, conservation du milieu naturel [082]

FRANCE ; ATLANTIQUE ; ARCACHON BASSIN

Fonds IRD [F B010096398]

fdi:010096398