International Journal of Aquaculture, 2025, Vol.15, No.2, 67-75 http://www.aquapublisher.com/index.php/ija 69 3 Theoretical and Scientific Foundations of Coral Reef Ecosystems 3.1 Coral symbiosis theory Corals can grow healthily, a large part of the reason they establish symbiotic relationships with some small algae called dinoflagellates. These algae belong to the family Symbiodiniaceae, which live in corals. These small algae can perform photosynthesis, convert sunlight into nutrients, and then provide them to corals. With these nutrients, corals can calcify, that is, build their own “skeleton” and help coral reefs grow little by little (Weis, 2019; Keeling et al., 2021). However, this partnership is fragile. If the sea water is too hot or the environment becomes worse, this symbiosis will be interrupted. As a result, corals lose color (bleaching) and even slowly die (Bove et al., 2022). To protect corals, we must first figure out how they cooperate with symbiotic algae, and we must understand them clearly from the cellular to the molecular level. 3.2 Principles of coral reef ecology Coral reefs are an ecosystem with a lot of biological species and very complex relationships. In this system, reef-making corals are the foundation. They have established relationships with many marine organisms, such as sponges, bryozoans and other cnidaria. These interactions help keep the whole system balanced and also make the reef more “resilient” in the face of damage (Montano, 2020). Scientists have a word called “coral holobiont”, which refers to the coral itself plus various microorganisms on it. This overall is important for coral health and determines whether it can adapt to environmental changes (Bourne et al., 2016; Putnam et al., 2017). So, figuring out how these organisms interact is very helpful for us to understand the ecological function of coral reefs and how they cope with stress. 3.3 Coral adaptation and evolutionary theories Now, many studies are focusing on one question: Can corals adapt to climate change ? The sea water temperatures are getting higher and higher, and if the corals cannot adapt, they will become extinct. Therefore, scientists have used many ecological-evolutionary models to study whether corals have this ability (Cropp and Norbury, 2020). Research has found that corals and their symbiotic algae can adapt to the new environment to a certain extent, so that the entire ecosystem has the opportunity to hold on. Moreover, symbiotic relations play a big role in this process. It not only provides nutrition, but may also help corals fight environmental stress. Therefore, if we want to improve the resilience of corals, we cannot ignore these symbiotic microorganisms (Apprill, 2020). To predict the future of corals or to develop conservation plans, you must first understand how they adapt to changes. 4 Major Challenges Facing Coral Reefs 4.1 Impacts of climate change and ocean acidification One of the biggest problems coral reefs face now is climate change and ocean acidification. These two problems are mainly because humans emit too much carbon dioxide. The more carbon dioxide, the higher the sea water temperature and the more acidic it is. This will make the coral very fragile. In many places, such as the Great Barrier Reef in Australia, large areas of coral bleaching occurs because of the heat of the sea water (Harvey et al., 2018). Scientists predict that if we do not control greenhouse gas emissions, most of the global tropical coral reefs may disappear between 2040 and 2050. Worse, corals evolve slowly and their environments get too fast, so they simply don’t have time to adapt (Hoegh-Guldberg et al., 2017). 4.2 Overfishing and destructive fishing practices Too much fishing is also hurting coral reefs, especially some destructive fishing methods, such as fried fish and poisonous fish. Not only does it catch all the fish, it also directly blows up the coral reefs or tramples. Some fish, such as herbivorous carp, are “cleaners” who help corals control seaweed. But these fish are caught too much, and seaweed grows wildly, so the corals cannot survive (Ahmad et al., 2021; Wilkins et al., 2021). The study also found that as the number of fish decreases, small corals (juvenile corals) also decreases. This can make it difficult to recover from coral reefs, especially after being hit by storms or pollution (Steneck et al., 2018). We need to promote sustainable fishing methods and establish marine protected areas (MPAs) to reduce these problems.
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