International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 260-266 http://ecoevopublisher.com/index.php/ijmec 263 growth rate, regenerative capacity or symbiotic density is difficult to return to the original level (Brown et al., 2023). In addition, the continuous deterioration of the environment (such as deteriorating water quality and nutritional imbalance) will also reduce the success rate of recovery. Habitat complexity and community structure also affect the settlement and growth of coral larvae, thereby determining the long-term recovery potential of the entire population. 5 The Evolutionary and Ecological Mechanisms of Coral Adaptation to Heat Stress 5.1 Adaptation and screening of symbiotic algae Symbiotic algae (Symbiodiniaceae) are an important component of coral heat tolerance. Different algae (such as Clade D, Clade C) show significant differences in heat tolerance. Corals can improve their heat tolerance by combining with more heat-tolerant symbiotic algae (such as certain symbiotic algal branches like Durusdinium trenchii and Cladocopium C15) (Cunning and Baker, 2020; Al-hammady et al., 2022). Long-term heat stress may lead to the screening of heat-tolerant symbiotic algae in coral populations (adaptive bleaching hypothesis). Furthermore, under the background of heat stress, the structure of symbiotic algal communities may be reassembled to enhance the heat tolerance of the overall host-algal system. Heat stress can disrupt the nutrient exchange between corals and algae, leading to coral bleaching (Figure 2) (Radecker et al., 2021; Marangon et al., 2025). Important heat-tolerant genes are involved in functions such as cellular stress response, membrane stability and metabolic reprogramming, and their expression characteristics can directly affect the tolerance threshold of corals to heat waves. Figure 2 Proportion of dividing algal symbiont cells on day 10 of heat stress (Adopted from Rädecker et al., 2021) Image caption: NanoSIMS images for 12C14N− were used to quantify the abundance of (A) regular and (B) dividing algal symbiont cells in the coral tissue sections (Adopted from Rädecker et al., 2021) 5.2 Adaptation mechanisms of coral hosts There are mainly two ways for corals to respond to heat stress: genetic alteration and plasticity. Selective breeding can help corals better withstand heat waves. Studies have shown that this method is highly effective (Moghaddam et al., 2021). Heat resistance is partly hereditary. It is estimated that genetic factors account for approximately 20% to 30% of this ability. Chemical markers on DNA are also very important. This is particularly important for young coral larvae. These markers will affect their future growth and health (Bisanti et al., 2025). Corals living in areas with drastic or frequent temperature changes usually have stronger adaptability. They can regulate metabolism and immune responses more precisely. This helps them tolerate higher temperatures. 5.3 Ecological adaptation strategies Corals use a variety of strategies to survive in the environment. They can adjust the breeding time. They may instead coexist with different types of symbiotic algae or migrate to cooler and more shady microhabitats. Some coral reefs experience significant daily temperature variations. These places can serve as "adaptive hotspots". Corals in these areas are usually better able to withstand heat waves (Banaszak et al., 2023).
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