International Journal of Marine Science, 2024, Vol.14, No.2, 102-110 http://www.aquapublisher.com/index.php/ijms 104 expand. In fact, one of the main causes of sea level rise over the past few decades is the thermal expansion of seawater. This effect is particularly obvious in surface seawater, which is directly heated by solar radiation and is more sensitive to temperature changes. It is worth noting that the thermal expansion and contraction effects of seawater do not occur uniformly. Due to the uneven distribution of ocean temperature and salinity and the influence of deep ocean circulation, the degree of thermal expansion and contraction of seawater in different sea areas varies. Seawater reaches its maximum density near 4 °C, so the thermal expansion and contraction behavior of water near this temperature is different from that at other temperatures. 1.3 Human activities The factors causing sea level rise due to human activities are multifaceted and complex. Their impacts are both direct and indirect, involving global warming, melting of glaciers and ice caps, thermal expansion and contraction of seawater, and groundwater and reservoir management. Together, these activities have driven significant sea level rise over the past century, with profound consequences for coastal communities, ecosystems, and the global climate. Global climate warming is the core factor causing sea level rise caused by human activities. With the acceleration of the industrialization process, large amounts of greenhouse gases, especially CO2, CH4 andN2O, are emitted into the atmosphere, enhancing the greenhouse effect of the atmosphere and causing the global average temperature to rise. This rise in temperatures directly accelerates the melting of glaciers around the world, as well as the Greenland and Antarctic ice sheets. As these bodies of ice enter the ocean, they not only increase the total volume of seawater, but also push up global sea levels. Human activities also indirectly affect sea level rise in other ways. For example, over-exploitation of groundwater and redirection of natural water bodies, such as through the construction of large dams and reservoirs, increase the amount of water flowing to the ocean, thereby affecting sea levels. Urbanization and the development of coastal areas have also changed the natural drainage system of the land surface and accelerated the rate of land runoff entering the ocean (Zheng et al., 2022). 2 Impact of Sea Level Rise on Marine Ecosystems 2.1 Changes and loss of coastal ecosystems Coastal ecosystems, including mangroves, salt marshes, coral reefs, seagrass beds, etc., are among the ecosystems on earth with the richest biodiversity and the highest ecological service value. They provide habitat, breeding grounds and food sources for many species, and also provide important ecological services to human society, such as coastline protection, carbon sequestration, water quality purification and support for economic activities. However, due to the impact of human activities and the intensification of global climate change, coastal ecosystems are experiencing unprecedented changes and losses, which poses a serious threat to biodiversity, ecological balance, and human well-being. Human activities are the main cause of change and loss of coastal ecosystems. Land use changes caused by urbanization and industrial development, reclamation, port and dock construction in coastal areas, etc. have directly destroyed the natural state of coastal ecosystems (Chen et al., 2023a). Agricultural expansion, overfishing and pollution (including plastic pollution, chemicals and heavy metal pollution) further exacerbate the degradation of coastal ecosystems. The introduction of invasive species also destroys the local ecological balance and affects the structure and function of the original biological community. Global climate change, particularly rising sea levels, increased ocean temperatures and ocean acidification, poses a major threat to coastal ecosystems. Rising sea levels have restricted the growth space of mangroves and salt marshes, affecting their growth and reproduction; rising ocean temperatures have led to widespread bleaching of coral reefs, threatening the health of coral reef ecosystems; ocean acidification has affected the calcification process of many marine organisms, thus affecting its survival and development.
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