International Journal of Aquaculture, 2024, Vol.14, No.1, 1-8 http://www.aquapublisher.com/index.php/ija 6 and Yi, 2021). The model incorporates two competing coral species that respond to future ocean warming and acidification through either the symbiotic algae switching mechanism (replacing existing algae types with more stress-tolerant types) or the symbiotic algae evolution mechanism. The model indicates that the switching mechanism is more effective, and the greatest impact on coral reef degradation is ocean warming rather than acidification. However, the ultimate outcome on a global scale will depend on the impact of warming and specific adaptive mechanisms. While the model provides a simplified representation of coral ecology and evolution, the research results enhance our understanding of coral adaptability. This understanding can help guide coral reef conservation efforts and suggest future research directions. 3.3 Antioxidative defense mechanisms Under conditions of high temperature and high light intensity, photosynthetic algae produce excessive oxidative substances, such as oxygen free radicals. These oxidative substances can damage the cells and tissues of hard corals, leading to coral bleaching. To counteract this stress, hard corals have developed a series of antioxidative defense mechanisms. Oxygen molecules possess strong oxidizing properties and are the main source of free radicals generated within an organism. If free radicals cannot be effectively cleared, they can cause damage to cells and tissues, leading to aging and even death of the organism. Therefore, antioxidants are crucial for organisms, as they can eliminate free radicals within the body, thereby protecting the cells and tissues of corals. Corals can obtain antioxidants through various pathways. On one hand, corals can self-synthesize antioxidants such as vitamins C and E to enhance their own antioxidative capacity. Additionally, corals can utilize exogenous antioxidants from marine microorganisms and seaweed in the ocean to enhance their antioxidant capacity. These microorganisms and seaweed contain carotenoids, polyphenols, flavonoids, and other antioxidative components, effectively clear free radicals within corals, providing protective effects. Hard corals can produce antioxidative substances, such as superoxide dismutase and catalase, to neutralize oxygen free radicals (Kramer et al., 2022). Hard corals can also adjust the rate of photosynthesis in symbiotic algae to reduce the risk of excessive production of oxygen free radicals. These antioxidative defense mechanisms help hard corals alleviate oxidative stress caused by climate change, thereby increasing their chances of survival. 3.4 Metabolic adaptations of hard corals Hard corals also exhibit metabolic adaptations to cope with different environmental conditions. When water temperature rises, the metabolic rate of corals increases, leading to faster growth. However, prolonged exposure to high temperatures can exert significant stress on corals, potentially leading to their death. To adapt to high-temperature environments, corals produce heat shock proteins, which protect the cellular structure and functions of corals from damage caused by elevated temperatures. Under high-temperature conditions, some hard corals can adjust their metabolic rates to reduce oxygen and symbiotic algae's demands (Zhang et al., 2021). This helps hard corals survive in high-temperature and low-oxygen environments, enhancing their resilience to the impacts of climate change. The biochemical adaptability mechanisms between hard corals and symbiotic algae enable them to seek new strategies to maintain their survival and reproduction in the face of climate change challenges. However, although these adaptive mechanisms can help hard corals cope with challenges in the short term, in the long term, they still face significant threats. Therefore, conservation and management measures remain crucial to ensure the ongoing existence of the relationship between hard corals and symbiotic algae, maintaining the ecological balance of coral reef ecosystems. 4 Summary and Outlook In nature, tropical hard coral reefs play an indispensable role in sustaining biodiversity and productivity in the global marine ecosystem. However, environmental changes triggered by climate change, especially elevated
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