Marine ecosystems capture carbon dioxide from the atmosphere and store it in the form of elemental carbon, acting as a “carbon sink”. Carbon stored in marine waters, be it in deep oceans or in the shallow coastal areas, is called “blue carbon”. Another example of the blue carbon sinks are the mangroves that inhabit coastal areas. Mangroves trap 10 times more carbon than their terrestrial counterparts and at up to 40 times the speed. Hence, with Seychelles’ 2195 hectares of mangrove forests, the country possesses abundant coastal blue carbon storage opportunities.
However, the same coastal features make Seychelles extremely vulnerable to climate change impacts such as sea-level rise and tropical cyclones. Hence, removing heat-trapping carbon dioxide from the atmosphere to mitigate climate change is a priority for the country. In part, this can be realised through the protection and restoration of mangrove ecosystems.
While qualitative data on the structure and composition of Seychelles’ mangrove networks are already available, there remains a big gap in quantitative information related to carbon storage capacity. This study aims to address this by collecting baseline information on local mangrove attributes such as height, diameter at breast height, and organic carbon content in soil. The resulting values give insights into Seychelles’ blue carbon storage capacity and solidify the case for mangrove protection, conservation, and restoration.
Field sampling estimates revealed that Aldabra holds the highest total carbon stocks, marked at 67% of the country’s total. This is expected as it is also home to 80% of Seychelles’ mangrove forests. Overall, the mangroves store almost 700,000 tonnes of organic carbon, 70% of which are trapped in soils. This is equivalent to 2.5 million tonnes of atmospheric CO2 removed from the atmosphere or 14,017 tonnes annually. In the national context, these coastal forests offset 3% of Seychelles’ annual CO2 emissions.
Analysis of field samples further uncovered that Seychelles’ mangroves captured carbon at a rate of 313.48 tonnes C/hectare, while the global average is between 702 to 856 tonnes of carbon per hectare of mangrove forest. This significant difference between global and local values further emphasises the need for local assessments to more accurately gauge country-specific blue carbon potential to avoid overestimating its offsetting capacity.
Overall, the outcome of this study quantifies the climate mitigation potential of
Seychelles’ mangrove forests using local field sampling results, and clarifies the role they play in supporting Seychelles to achieve its Nationally Determined Contributions commitments.