Coral reef restoration strategies use natural and anthropogenic processes to restore damaged coral reefs. Reefs suffer damage from a number of natural and man-made causes, and efforts are being made to rectify the damage and restore the reefs. This involves the fragmentation of mature corals, the placing of the living fragments on lines or frames, the nurturing of the fragments as they recover and grow, and the transplantation of the pieces into their final positions on the reef when they are large enough.
Background
Coral reefs are important buffers between the land and water and help to reduce storm damage and coastal erosion. They provide employment, recreational opportunities and they are a major source of food for coastal communities. It is estimated that $375 billion dollars come from ecosystem services provided by coral reefs each year.
The most prevalent coral in tropical reefs are the stony corals Scleractinia that build hard skeletons of calcium carbonate which provide protection and structure to the reef. Coral polyps have a mutualistic relationship with single-celled algae referred to as zooxanthellae. These algae live in the tissue of coral polyps and provide energy to the coral through photosynthesis. In turn, the coral provides shelter and nutrients to the zooxanthellae.
Half the world's coral since 1970 have disappeared, and all reefs being threatened with extinction by 2050. In order to ensure the existence of coral reefs in the future, new methods for restoring their ecosystems are being investigated. Fragmentation is the most common strategy for restoring reefs; often used to establish artificial reefs like coral trees, line nurseries, and fixed structures.
Threats to coral reefs
Some anthropogenic activities, such as coral mining, bottom trawling, canal digging, and blast fishing, cause physical disruption to coral reefs by damaging the corals' hard calcium carbonate skeletal structure.
Another major threat to coral reefs comes from chemical degradation. Marine pollution from sunscreens, paints, and inland mining can introduce chemicals that are toxic to corals, leading to their decay. Coral disease is often prevalent in areas where coral are stressed, and has increased in severity in recent decades. Often a result of pollution, eutrophication can occur in coral reef ecosystems, limiting nutrients from the corals. With changes happening on coastal lands such as deforestation, mining, farm soil tiling and erosion, much more sediments are entering the water column. This is known as sediment loading, which can directly smother the coral, or block UV light, effectively blocking the coral from photosynthesizing.
Additionally, increased CO2 emissions from human activities such as fossil fuel burning can effect the acidity of ocean waters. Ocean acidification occurs when excess CO2 reacts with ocean water and lowers the pH. Under acidic conditions, corals cannot produce their calcium carbonate skeletons, and certain zooxanthellae are not able to survive.
Perhaps the biggest threat to coral reefs comes from rising global temperatures. Most corals can only tolerate a 4-5 °C range in water temperatures. Under these adverse conditions, corals may expel their zooxanthellae and become bleached. As ocean waters warm beyond the tolerated temperature range, corals are dying. One study of the Great Barrier Reef found the reef mortality rate to be 50% after an extreme heatwave with 3-4 °C temperature increase. Due to bleaching events similar to this one, injured corals continue to die after the event due to increased disease susceptibility, it takes decades after bleaching events for the reef to recover, and the slow growing corals are put under an immense amount of stress. The rising global temperature is a consequence of releasing high amounts of greenhouse gases into the atmosphere. A study showed that about 655 million people live close to coral reefs, accounting for 91% of the world's population who are part of developed countries such as The United States of America, the Middle East and China. The same study also revealed that of the 655 million people, 75% of the population living in close proximity to coral reefs are from poorly developing countries and even though these low-developing countries depend on the coral reef ecosystem they only contribute to a small fraction of greenhouse emissions. Emission statistics have shown that developed countries contribute to about 11 times more greenhouse gas emissions than poor developing countries.