Research on blue carbon stocks in Vietnam's coastal seagrass beds

Dr. Cao Van Luong on a survey and sample collection diving trip

Seagrass - A reliable carbon sink

Seagrasses are the only group of flowering plants that live in marine and brackish environments. Seagrass beds are vital habitats for coastal aquatic organisms, especially in tropical coastal regions. Beyond their ecological value, seagrass ecosystems are recognized for their significant role in environmental regulation due to their ability to store large amounts of organic carbon. Globally, seagrasses are estimated to store about 19.9 billion tons of organic carbon, which is 2-3 times higher than evergreen forests per unit area. Their carbon absorption rate is 35 times faster than that of tropical rainforests. Although seagrass beds occupy only 0.2% of the global area, they contribute 10-18% of the organic carbon in marine ecosystems, with an average annual accumulation of 48-112 million tons.

Conserving and expanding seagrass beds is considered a natural solution to support efforts in mitigating and adapting to climate change. In recognition of this, the Third International Seagrass Conference, held in Manila (Philippines) in April 1998, adopted the "Seagrass Charter" addressed to the UN Secretary-General, urging maritime nations to prioritize the protection and development of seagrass resources. The restoration of this crucial ecosystem was also included in climate change mitigation plans, as 159 seagrass-holding nations signed the Paris Agreement in 2015.

Vietnam, with over 3,260 km of coastline and more than 50,000 km² of territorial waters (according to the Ministry of Foreign Affairs, 2002), boasts a rich coastal aquatic flora, regarded as a massive blue carbon ecosystem. Seagrasses are recognized for their important role in carbon absorption and storage. However, research on the carbon absorption and storage capabilities of underwater ecosystems, including seagrass ecosystems in Vietnam, remains limited. In national inventory reports, seagrasses have not received the same attention as terrestrial vegetation. Calculating and determining the organic carbon stocks in coastal seagrass beds will contribute to the scientific basis for Vietnam's efforts to reduce greenhouse gas emissions, and mitigate and adapt to climate change.

Research Findings

Aiming to determine the organic carbon stocks in representative seagrass beds in some coastal regions of Vietnam and propose effective and sustainable management, exploitation, and use strategies for seagrass ecosystems in these areas, Dr. Cao Van Luong and his colleagues at the Institute of Marine Resources and Environment conducted the project: "Research on Determining Blue Carbon Stocks in Seagrass Beds in Vietnam's Coastal Regions" (Code VAST06.01/22-23).

Study site map

Seagrass beds and coral reefs

In this study, the scientists developed and updated four detailed maps of seagrass distribution in Ha Dong, Cua Gianh, Van Phong and Phu Quoc, adding them to the seagrass distribution database and mapping system in Vietnam. The total dry biomass in the four study areas reached 67,097.4 tons. The total organic carbon stocks in seagrass beds (biomass and sediment) in the four study areas reached 346,032.6 tons of Corg (40.12 tons of Corg/ha). The estimated total organic carbon stock of Vietnam's seagrass beds is 878,026 tons of Corg, equivalent to 3,222,356 tons of CO2 or 3,222,356 carbon credits. Through this study, Dr. Luong and his colleagues estimated the value of organic carbon stocks in Vietnam's seagrass beds to be approximately 64.447 million USD.

Based on the research results, the scientists proposed solutions for the effective and sustainable management and use of seagrass ecosystems, while also developing and expanding seagrass conservation areas. In addition to maintaining and restoring coastal ecosystems, the study provides a scientific basis for Vietnam to prepare for participation in regional and global carbon markets.

Dr. Cao Van Luong noted that these are initial successes, and the research results are immediate evaluations over two years. For more accurate results on seagrass ecosystems, long-term monitoring, evaluation and research on seagrass bed services are needed in the future. Moreover, it is essential to supplement research on seagrass beds in offshore areas, such as some archipelagos in the Gulf of Thailand. Finally, specific actions are required from management agencies, stakeholders, and policymakers to strengthen the management and further attention to seagrass beds in Vietnam.

Translated by Phuong Huyen
Link to Vietnamese version