International Journal of Marine Science, 2024, Vol.14, No.1, 14-20 http://www.aquapublisher.com/index.php/ijms 18 Figure 4 Process of ocean acidification The acid-base balance in the ocean plays a role in many chemical reactions, where carbonate ions and hydrogen ions react with calcium ions (Ca2+) to form calcium carbonate (CaCO3), which is an important process for corals and other marine invertebrates to form bones and shells. Carbonate ions and hydrogen ions react with boric acid (H3BO3) to form quaternary salt ions (B (OH) 4-), which are crucial for the cycling of boron in the ocean and the metabolic processes of organisms. Carbonate ions and hydrogen ions react with iron ions (Fe3+) to form iron carbonate, helping the iron cycle in the ocean and the growth and development of organisms. PH value is an indicator of the acidity and alkalinity of a solution. Ocean acidification causes an increase in the concentration of hydrogen ions in seawater, leading to a decrease in pH value (Luan et al., 2023). The pH value of normal seawater is approximately 8.1~8.3, while in areas affected by ocean acidification, the pH value may decrease to 7.8 or lower (Chen et al., 2016). 3 Physiological Effects of Ocean Acidification on Corals 3.1 The impact of ocean acidification on coral growth and bone formation Ocean acidification leads to a decrease in the concentration of carbonate ions (CO3 2-) in seawater, and corals utilize the carbonate ions and calcium ions (Ca2+) in seawater to form their skeletal structures. However, due to acidification and the scarcity of carbonate ions, corals face a shortage of calcium ion supply, which limits the formation and growth of bones (Morgado et al., 2022). In acidic environments, the calcium content in coral bones decreases and the quality of the bones weakens, making the structure of corals fragile and susceptible to external pressure and damage, such as storms, waves, and physical damage, and directly affecting the growth rate of corals. In an acidic environment, corals require more energy to absorb and utilize the scarce carbonate and calcium ions in seawater, slowing down the growth process of corals and resulting in a slower overall growth rate. Weakening the immune system of coral makes it difficult to resist attacks from pathogens and other stress factors, making it more susceptible to disease and infection, increasing the risk of coral disease and death. The limited growth and decreased bone mass of corals pose a threat to the overall health and stability of coral reefs. The reduction of corals can lead to a decrease in the biodiversity of coral reef ecosystems, affecting the survival and reproduction of many species that rely on coral reefs. 3.2 Impact of ocean acidification on nutrient uptake and metabolism of corals Corals are the cornerstone of coral reef ecosystems, providing habitats and food sources for other organisms. Ocean acidification has a negative impact on the survival and growth of corals, leading to a decrease in coral coverage and degradation of coral reef structures. Ocean acidification may affect coral's ability to absorb nutrients such as nitrogen and phosphorus. Under such conditions, the permeability of coral cell membranes may change,
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