International Journal of Marine Science, 2024, Vol.14, No.1, 57-65 http://www.aquapublisher.com/index.php/ijms 59 processes. Calcification is a crucial process for many marine organisms, including corals, shellfish, certain plankton, and algae, to construct shells or skeletons, which are mainly composed of calcium carbonate. As ocean acidification increases, the concentration of carbonate ions available for biological calcification in seawater decreases, which directly affects the ability of organisms to build and maintain their calcium carbonate structures. For coral reefs, acidified water slows the growth of coral skeletons, reducing their structural integrity and ability to withstand external stresses. Not only does this reduce the biodiversity habitat that coral reefs provide, it also reduces their role in coastal protection, such as mitigating storm-induced erosion and wave action. Shellfish and certain plankton are also severely affected by ocean acidification. The calcification process becomes more difficult for these organisms, affecting their survival, growth and reproduction. Especially for plankton at the bottom of the marine food web, calcification barriers will affect the energy flow and material circulation of the entire marine ecosystem because they are the basis of the food chain of many marine organisms. The impacts of ocean acidification on marine life are not limited to calcification processes. Changes in pH may also affect physiological functions of organisms, such as respiration, sensory orientation, and reproductive capabilities, thereby further affecting population health and biodiversity. 2 Key Challenges Facing Marine Life 2.1 Decline in biodiversity The decline in biodiversity of marine ecosystems is a growing global problem that poses a huge threat to the marine environment and other biological populations. The decline in marine biodiversity not only reduces biological species, but also damages the structure and function of marine ecosystems, affecting the ecological services they provide, such as carbon cycle, oxygen production and food web stability. Habitat change and loss is one of the main causes of global biodiversity decline, with a particularly serious impact on marine ecosystems. Marine life's habitats, including coral reefs, mangroves, seagrass beds, coastal wetlands and deep-sea environments, are affected to varying degrees by human activities and climate change. These habitats provide food, shelter and breeding grounds for marine life and are key to maintaining marine ecological balance and biodiversity. The impact of climate change on marine ecosystems is also a key factor in the decline of biodiversity. Rising ocean temperatures, ocean acidification, and sea level rise have put tremendous pressure on the living environment of marine organisms (Giddens et al., 2022). These changes not only affect the physiology and reproduction of organisms, but also change species distribution and migration patterns, further exacerbating the loss of biodiversity (Figure 1). Pollution is also an important reason for the decline of marine biodiversity. Plastic pollution, heavy metals and chemical contamination have toxic effects on marine life, affecting their health and ability to reproduce. In particular, the widespread presence of plastic particles has become a persistent threat to marine ecosystems. The emergence of invasive species has also put pressure on marine native species to compete and replace them, changing the structure of local biological communities and further threatening biodiversity. The introduction of these alien species is often caused by human activities, such as through ships' ballast water or marine aquaculture activities. 2.2 Changes in food webs Changes in food webs reflect complex adjustments to species relationships and energy flows within ecosystems, and such changes are particularly significant in the context of global climate change. Climate change is altering the food web structure of many ecosystems indirectly or directly by affecting environmental factors such as temperature, precipitation patterns, and ocean chemistry. These changes not only affect individual species, but also affect the interactions between species and the functions of the entire ecosystem (Tan et al., 2022).
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