Assessment of blue carbon stocks and seagrass health dynamics in the Gulf of Tunis: case study of the Sidi Rais barrier reef

Climate change is a major global environmental challenge, and marine vegetation, or blue carbon habitats, are crucial in mitigating it by storing large amounts of atmospheric CO ₂ . These ecosystems are highly effective at carbon sequestration. This study is among the first in Tunisia to assess the carbon storage capacity of seagrass meadows. By quantifying the total organic carbon (TOC) in three cores collected approximately 100 m offshore from the beach at the Posidonia oceanica barrier reef, with water depths ranging from 0.5 to 2.0 m, and using remote sensing to map the seagrass beds, we determined both short and long-term carbon sequestration. Results highlight the considerable carbon sequestration potential of seagrass ecosystems. The short-term carbon storage capacity, estimated at 137.6 gC m ^− 2 yr ^− 1 , whereas the long-term sequestration flux reached 32 gC m ^− 2 yr ^− 1 . These results underline the importance of seagrass beds in both short-term carbon uptake and long-term storage on the Tunisian coast. It has also been found that the Sidi Rais seagrass bed, an important marine ecosystem, stores annually around 15,864 tonnes of CO ₂ , compensating for 6.8% of annual local CO ₂ emissions, estimated at 233,486 tonnes per year for 849,184 inhabitants in 2019. Despite their role in carbon sequestration, seagrass cover has alarmingly declined from 133 hectares (2009) to 97 (2015) and, more recently, 51 hectares in 2021, according to mapping results. This work aligns with the growing evidence of the contribution of seagrass to climate change while highlighting the need to preserve it on the Tunisian coast.