International Journal of Marine Science, 2025, Vol.15, No.4, 220-232 http://www.aquapublisher.com/index.php/ijms 223 introduction of human activities, but they pose a long-term threat to the health of mangroves, which in turn weakens their carbon sink capacity. Tropical storms, hurricanes and typhoons often rage mangrove areas, and strong storm surges can destroy large areas of mangroves in a short period of time. Taking the tropical cyclone "Nargis" that attacked Myanmar in 2008 as an example, it caused more than 35% of mangroves in the Irrawaddy Delta to be destroyed, and the carbon stocks accumulated over decades were released. Gradually induced environmental pressures such as sea level rise, extreme high temperatures and droughts, etc., are also seen as potential threats to mangroves (Liu et al., 2024). For example, sea level rise increases the risk of mangroves being submerged. If the siltation rate does not match the Shanghai plane rise rate, the mangroves may retreat or even die out, and the stored soil carbon is reexposed. 3.3 Large-scale shrimp farming in Southeast Asia leads to mangrove degradation and carbon loss Large-scale shrimp farming in Southeast Asia is one of the most representative cases of mangrove degradation and carbon loss. Since the 1970s, a craze for shrimp exports has been set off in coastal areas such as Thailand, Vietnam, and Indonesia. Large areas of mangrove forests have been cut down and ponds have been dug for construction of shrimp fields (Hashim et al., 2021). It is reported that between the 1970s and 1990s, about one-third of mangrove losses in Southeast Asia could be attributed to the expansion of the shrimp farming industry. This industrial-driven land use change has severely damaged the function of mangrove carbon sinks: first, the original mangrove vegetation was completely removed, and a large amount of carbon stored in the trees was immediately lost; more hidden but far-reaching, the excavation of shrimp ponds exposed the mangrove peat soil layer to the air, and the organic carbon accumulated in the soil that has been accumulated for hundreds of years is quickly decomposed by microorganisms and released into CO₂ and methane. According to research estimates, every hectare of mature mangroves clearance can cause soil and vegetation carbon reservoirs to release hundreds of tons of carbon dioxide equivalent to the atmosphere. If the disturbances to soil and periodic drainage during shrimp pond operation are taken into account, carbon emissions will be further increased. Not only that, many shrimp farming ponds were abandoned after several years of operation due to diseases or deterioration of water quality, leaving behind bare ground and salinized mud bottoms that are difficult to recover. These degraded lands often cannot grow back into mangroves for many years, which means that carbon sink function is lost for a long time and may even be converted into a net carbon source. The lessons of the large-scale replacement of mangroves in Southeast Asia by shrimp ponds are profound: short-term economic benefits cause huge ecological costs and destroy valuable blue carbon pools (Rahman et al., 2024). In recent years, with the global re-understanding of the value of blue carbon, some Southeast Asian countries have begun to take measures to curb the further transformation of mangroves into breeding ponds. Vietnam and Thailand have introduced coastal land use control policies, prohibiting new shrimp farms in key mangrove areas, and encouraging ecological restoration of abandoned shrimp ponds (Figure 1) (McSherry et al., 2023). However, restoring lost carbon reserves is not easy and takes decades of effort. The case in Southeast Asia shows that anthropogenic land use changes can significantly regress the function of mangrove carbon sinks in a short period of time, emphasizing the importance of strengthening coastal planning management and preventing blind aquaculture expansion. This is also the lessons that must be learned from promoting the protection and restoration of mangroves and achieving carbon sink improvement. 4 Strategies and Technologies for Mangrove Restoration 4.1 Comparison of natural recovery and artificial assisted recovery technology For the recovery of degraded mangroves, two technical paths can be adopted: natural recovery and artificial assisted recovery, each with its advantages and disadvantages and applicable conditions. Natural recovery refers to restoring stands by relieving stressors and improving environmental conditions, relying on the natural diffusion and renewal capabilities of mangroves themselves. For example, stop interference and restore tidal channels, so that the seeds and combrots adjacent to healthy mangroves spread to the degraded areas with the flow of water, and naturally germinate into forests. This method is low in cost and has less manual intervention, and the recovered communities are often more ecologically adaptable and diverse. In areas with a highly degraded and isolated from mangrove mother sources, it may be difficult to re-establish mangrove vegetation by relying solely
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