Human threats to coral reefs and coral damage

In 2001, it was estimated that 58% of the world’s coral reefs were threatened by human behaviour (Spalding et al., 2001). While there is debate over whether coral bleaching is a naturally occurring event or largely caused by humans, there are many causes of coral destruction that are undoubtedly anthropogenic.

Firstly, overfishing is regarded as one of the main anthropogenic threats to reefs. This has a direct impact on the ecosystem as the balance of producers, consumers and predators is shifted, but the indirect consequences of this are also significant. As many reef fish are herbivores, feeding on algae, removal of these consumers leads to high rates of algal growth on the surface of corals. Unlike the algae living within the coral polyps, these algae are larger, fleshy algae and are incapable of forming a symbiosis with the coral. Instead, they can reproduce at rapid rates and completely cover large surface areas of corals at a very high rate. This can either suffocate the corals, because of the increased levels of algal respiration leading to decreased levels of oxygen, or can block sunlight from reaching the intracellular zooxanthellae (Roberts, 1995). The latter means the zooxanthellae cannot photosynthesise, leading to their death, which can also lead to coral death as the polyps will no longer be receiving nutrients from the zooxanthellae. In many countries, fishing within coral reefs has become such a large source of income that it is being carried out at unsustainable levels. In order to try and allow fishing to proceed at sustainable levels, regulations need to be put in place to prevent overfishing.