International Journal of Aquaculture, 2025, Vol.15, No.2, 67-75 http://www.aquapublisher.com/index.php/ija 68 abundant species, it is often called the “tropical rainforest of the ocean”. Although coral reefs account for less than 0.1% of the ocean area, they provide space for about a quarter of marine life. These organisms include various fish, shrimp, crabs, and many invertebrates (Nama, 2020). Corals, especially stony corals, can form complex structures. These structures provide “home” and food for many marine life. Different species of animals can find their own place here and form many interdependent relationships. These relationships help keep the ecosystem healthy and balanced (Principe et al., 2021). But the problem arises. Climate change and human activities have led to many coral degradation. This puts the otherwise abundant ecosystem at great threat (Nelson et al., 2016). 2.2 Functions and roles of coral reefs in marine ecosystems Coral reefs are not just habitats in the ocean, they have many other important functions. First, it provides food and shelter for various marine animals. At the same time, coral reefs are also involved in energy flow and nutrient circulation in the ocean. In this system, there are many interactions between microorganisms, sponges, benthic animals, etc. For example, a sponge absorbs organic matter from water and then releases small molecules. These small molecules can be used by microorganisms. Then, microorganisms become food for larger animals, which forms a cycle. This process is called "sponge ring". It helps coral reefs maintain high biodiversity and yields in water with little nutrients. In addition, microorganisms play two roles in coral reefs. Some are good for corals, such as helping them grow; but some may become pathogens when corals are stressed, causing disease or coral bleaching (Figure 1) (Vanwonterghem and Webster, 2020). Even if the coral dies, the skeleton structure it leaves behind can keep some invertebrates living there. However, if these structures are destroyed, biodiversity will also decline. Research has found that marine protected areas can make coral reef systems stronger by protecting fish populations and species. Especially some fish that eat seaweed can help control algae growth and give corals a better living space (Topor et al., 2019). Figure 1 Cycling of dissolved and particulate organic matter through the microbial and sponge loops (Adopted from Vanwonterghem and Webster, 2020) 2.3 Contributions of coral reefs to coastal communities and economies Coral reefs are very important to people in many coastal areas. The services they provide include: preventing coastal erosion, providing fish resources, attracting tourists, etc. Millions of people around the world rely on coral reefs to survive. But now, issues such as climate change, pollution and overfishing are degrading coral reefs. Once the coral system collapses, many people who rely on it may lose their jobs, causing local economic difficulties and social problems (Hoegh‐Guldberg et al., 2017). Therefore, it is very important to protect the diversity and ecological functions of corals. Only in this way can we ensure that these ecosystems continue to provide services that help humanity (Ng et al., 2022).
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