Inventorying carbon stocks of protected European blue carbon ecosystems: first outcomes from a systematic review

Among the several ecosystem services provided by seagrasses, saltmarshes and mangroves, carbon sequestration and long-term storage in sediments is receiving increasing attention as a possible nature-based solution contributing to climate change mitigation. Therefore, an inventory of available data on the carbon stocks of blue carbon (BC) ecosystems is of crucial importance to understand the extent of the contribution of such a nature-based solution and to guide management practices towards conservation and restoration strategies. In this study we reviewed the state of knowledge on carbon stocks of European BC systems in protected and unprotected sites, with the aim to emphasize their role as key ecosystem service providers that should be included in conservation priorities. A systematic review approach was used to assess the literature focusing on European seagrass and saltmarsh habitats. A total of 661 data were extracted from 47 papers out of 832 retrieved that were published between 1994 and 2023. Most of the sites of the 18 countries inventoried were protected under the Natura 2000 Habitats Directive (EU countries) or were Special Areas of Conservation (non-EU counties). The top meter soil Corg stocks (kg Corg m-2) of seagrass habitats was significantly higher in protected sites than in unprotected sites, but not in saltmarsh habitats. The results of this study provided baseline information on BC systems at the European level and revealed a lack of data in most of the Mediterranean basin, suggesting the need to increase the spatial coverage of carbon stock studies, especially in Mediterranean Marine Protected Areas. In this context, protected areas can serve as valuable laboratories to test the effectiveness of protection on the potential of the BC systems and can help to provide a more comprehensive picture of their potential role in climate change mitigation.