Coral reefs are marine ecosystems that are important for recreational, tourism, commercial, and fishery industries around the world. Diverse plants and marine animals in the coral reef ecosystem provide a rich resource from where scientists obtain natural products to treat a wide variety of diseases. Many countries depend on coral reefs for food. The varied biodiversity gives rise to a marine aquarium industry; however, this rich habitat is being threatened by natural and human threats. Overfishing is significantly altering the ecological balance, contributing to its degradation.
Overfishing promotes algae growth
Dense populations of sea urchins and grazing fish on the coral reef ecosystem often help maintain low levels of algae. On reefs where the abundance of fish and invertebrates is significantly large, the algae present in the reef ecosystem is maintained naturally at small growth rates. Scientific experiments have revealed that the depletion of fish grazers from the reef due to disease or overfishing can promote reproduction of algae subsequently surpassing the rate at which corals grow. This may eventually cause an over shift where corals are replaced by fast-growing seaweed.
Overfishing of predatory fish
Overfishing of predatory fish, such as triggerfish, leads to a chain of events that affects the coral reef ecosystem. Triggerfish are natural predators of sea urchins. Overfishing of this fish promotes overpopulation of sea urchins. Sea urchins, in turn, reduce the abundance of coralline algae by excessive grazing. coralline algae play an important role in the life-cycle of coral polyps. coralline algae secrete calcium carbonate, forming a hard carbonate shell on the substrates where they adhere to. This helps build the limestone structure of coral reefs; however, the grazing of crustose coralline algae significantly affects the coral reef habitat.
Overfishing of herbivores
Overfishing of certain types of fish can significantly affect the coral reef biodiversity. Some fish, such as the grouper, feed on corals by creating holes in them. The algae grows in those wholes, over time, smothering the coral. Overfishing of fish that feed on marine plants can affect the ecological balance and biodiversity of the reef, leading to increased levels of algal growth. The rich biodiversity of marine species in the coral ecosystem has promoted the biomedical, aquarium and aquaculture industries. Overfishing of certain marine species for commercial purposes has decreased marine populations.
Fishermen sometimes use dynamite and cyanide to stunt the fish in the coral reef. The high demand of certain fish species and the abundance of them in the reef has promoted the practice of this damaging fishing technique. These fishing practices generally are not target specific to certain species and often a number of species are killed in the process. Cyanide fishing is a practice during which sodium cyanide is sprayed into the target fish's habitat so as to stunt the fish. The fishing method not only damages the fish population, but also other marine animals and plants, affecting the whole coral reef ecosystem.
Marine species inhabiting the reef depend on each other for survival. Overfishing breaks the links in the food chain, from the zooxanthellae, which lives in a mutualistic relationship with the coral to bigger marine predators which feed on smaller fish. While smaller marine species, lower in the food chain, may prosper, this can lead to an unbalanced ecosystem, eventually destroying the reef ecosystem. According to nceas.ucsb.ed, the coral reef ecosystems are among the most highly productive and diverse ecosystems in the world, but are, in the present. threatened by natural and anthropogenic causes. Coral reef degradation leads to an irreversible damage where the dominance of corals is replaced by dominance of seaweed or fleshy macroalgae.