International Journal of Aquaculture, 2025, Vol.15, No.2, 57-66 http://www.aquapublisher.com/index.php/ija 62 decreases, the phytoplankton that they originally ate will increase in a large number. This will cause the water to turn green and turbid, which is eutrophication. After the water quality deteriorates, the ecological balance in the lake may be disrupted. Therefore, controlling carp populations, especially invasive species, is an important step in protecting lake ecology (Razlutskij et al., 2021; Hochstrasser and Collins, 2024). 6.3 Multi-trophic interactions in coral reef ecosystems There are many kinds of organisms living in coral reef ecosystems, and the nutritional relationship is also very complex. From the bottom phytoplankton to the grass-eating fish to the top vegetarian predators, everyone depends on each other. If the environment changes, such as too much nutrients in the water or too much temperature fluctuation, these relationships are easily broken. Community structure may change, and the entire ecosystem may become unstable (Lomartire et al., 2021). Here, zooplankton plays a very critical role. They eat phytoplankton and are eaten by more advanced animals, such as coral fish and some filter feeders. The fatty acids and sterols in the body of zooplankton are very important to their own growth and also affect the nutritional status of the upper animals. These nutrients are also different, they will vary depending on the type of zooplankton, what they eat and living environment. For example, some zooplankton eat specific types of food, so their nutrition will be different in their bodies. When coral reefs are under external pressure, such as rising water temperatures or excessive nutrients in the water, the nutrient structure of zooplankton also changes. This change may affect the operation and balance of the entire food web (Figure 3) (Thomas et al., 2022). Figure 3 Effects of nutrient manipulation differ based on zooplankton genus and broad nutrient type (Adopted from Thomas et al., 2022) 7 Challenges Facing Aquatic Ecosystems 7.1 Impact of overfishing on trophic balance Catching too many fish in the water, especially catching the top predators, will break the original nutritional balance of the ecosystem. If these predators are gone, the number of prey they originally controlled will increase rapidly. In this way, some species may be too many, while others will become less, causing chaos in the entire food web. Such changes may make ecosystems unstable and may also reduce biodiversity (Mao et al., 2020). Moreover, the disappearance of top predators may also cause the number of phytoplankton and zooplankton to be out of control and cannot maintain the “top to bottom” regulation. The result may be that algae grow wildly, and algae blooms appear, which makes the water quality worse (Su et al., 2021).
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