International Journal of Marine Science, 2025, Vol.15, No.4, 220-232 http://www.aquapublisher.com/index.php/ijms 222 also bring about differences in carbon sink functions. For example, the dominant stands of mangrove families usually have higher xylem carbon content and underground root input, resulting in higher carbon reserves (Sigamani et al., 2023). 2.3 Effects of natural conditions on carbon sink function (tidal, salinity, etc.) The function of mangrove carbon sinks is also regulated by local natural environmental conditions, among which tidal law and salinity are two key factors. Tides not only bring nutrients and sediments to mangroves, but also affect the soil flooding cycle, thus having a dual effect on carbon sinks. Moderate tidal flooding helps bury organic carbon: as the tide rises and falls, suspended organic matter and sediment are deposited on the mangrove subsoil to form a new carbon layer; at the same time, frequent flooding creates an oxygen-deficient environment and slows down the decomposition of organic carbon in the soil. However, overly strong currents may also wash away the yet-stable organic debris, reducing carbon retention (Yong et al., 2024). Therefore, there are differences in the carbon sink effect of mangroves under different tidal amplitudes and frequencies. Generally speaking, silt environments such as the estuary delta are more conducive to mangrove carbon deposition than the scattered coast (Fu et al., 2025). Salinity indirectly regulates carbon sink function by affecting the activity of mangrove plants and soil microbial activities. In mangrove environments with lower salinity or freshwater input, trees grow faster and produce more biomass, which is conducive to carbon accumulation; but freshwater erosion may increase the rate of organic matter decomposition. In addition to tides and salinity, factors such as temperature, rainfall, and nutritional levels will also affect the growth and carbon dynamics of mangroves. For example, high temperatures can prolong mangrove growth period and increase photosynthesis intensity, but extreme high temperatures or droughts may lead to mangrove stress and even death, thereby releasing carbon reserves (Rodda et al., 2022). 3 Analysis of the Causes of Mangrove Degradation and Decline in Carbon Sink Function 3.1 Coastal development, breeding and deforestation pressure Human activities are the main reason for the accelerated degradation of mangroves and the decline in carbon sink functions in modern times. Large-scale development in coastal areas directly leads to the loss of mangrove habitats. When ports, urban infrastructure and tourism facilities are built in coastal areas in many countries, large-scale land reclamation has been reclaimed, destroying the original mangrove wetlands. At the same time, the emission of industrial and urban domestic sewage causes the deterioration of coastal water quality, further affecting the growth and survival of mangroves (Passos et al., 2022). Secondly, the expansion of aquaculture industry has put great pressure on mangrove ecology. Since the 1970s and 1980s, a prawn farming boom has emerged around the world, especially in Southeast Asia, and a large number of mangrove swamps have been cleared and dug into shrimp ponds and fish ponds (Mitra and Sikder, 2023). According to statistics, during this period, mangrove losses caused by aquaculture development accounted for 30%~50% of the total losses. Once mangroves are replaced by breeding ponds, they not only lose the carbon fixation capacity of live trunks, but also the carbon accumulated in the original soil is also rapidly oxidized due to excavation and exposure, and converted into CO₂ and discharged into the atmosphere. Again, excessive cutting and timber collection are also important human factors in mangrove degradation. In some underdeveloped coastal areas, mangroves have been cut down by local residents for fuel, wood and charcoal, exceeding the forest’s own regeneration capacity, resulting in forest land degradation or even complete disappearance (Gowda et al., 2025). In addition, coastal agricultural reclamation, salt field development, etc. also occupy a large amount of mangrove habitat. 3.2 The impact of invasive species and natural disasters In addition to direct man-made destruction, ecological invasions and natural disasters can also lead to mangrove degradation, which in turn affects its carbon sink function. In some mangrove areas, invasive alien species are changing the structure and function of local ecosystems. For example, some invasive plants (such as saline herbs such as serrata) spread in mangrove habitats, which may compete with young mangrove plants for space and nutrients, hindering the natural renewal of mangrove forests. In addition, invasive herbivores or insects (such as some mangrove-eating beetle larvae) will also cause damage to mangroves and reduce stand density and vitality when they reproduce in large quantities. These ecological invasions are often the result of unintentional
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