Coral Reefs

(CC) Image by Nick Hobgood

Coral reefs are one of the most diverse ecosystems on earth, second only to the rainforests in terms of biodiversity. Covering less than one tenth of one percent of the oceans surface area, coral reefs are home to over 2 million species and 25% of all marine life. Coral reefs are made up of both hard corals (Scleractinia) which have rigid exoskeletons and soft corals (Gorgonians) which lack an exoskeleton and sway with the oceans current. Climate change along with a combination of factors including overfishing, sediment runoff and unsustainable tourism are all contributing to the rapid decline of the world’s coral reefs. Without swift action, the precious marine ecosystems could disappear along with thousands of marine species.

The Importance of Coral Reefs

The coral reef ecosystem is a vital source of food and shelter for many different species of fish, mollusk, sponge, cetacean, sea turtle and crustacean. Coral reefs are also vital for absorbing carbon dioxide as coral polyps turn carbon dioxide into limestone shells, which helps coral reefs expand. Without coral to absorb vast quantities of CO2, the ocean would become more acidic and this would affect a huge number of ocean species. Another importance aspect of coral reefs is that they act as coastal barriers by slowing waves before they reach shore, helping to prevent floods and tsunamis. Coral reefs also help reduce the impact of hurricanes and typhoons, which ravage coastal areas.

Coral Bleaching

Increased ocean temperatures, as a result of global warming and pollution, place coral organisms in an extremely vulnerable position as coral is hypersensitive to temperature change. Coral bleaching occurs when coral polyps release the algae inside them when exposed to increased heat, changes in water acidity, increased sediment and ultraviolet radiation. Essential for the corals survival, the algae provides up to 80% of a corals energy. When these algae are released en masse, it can result in the bleaching of a coral. Coral reefs in the Maldives, Tanzania, the Seychelles, Kenya and Sri Lanka have been reduced by 90% due to increased sea temperatures and coral bleaching.

Overfishing

Commercial fishing practices, occurring on a massive scale, threaten the ecological balance of reefs by damaging the food chain. The Wildlife Conservation Society working in conjunction with the University of California at Santa Cruz, conducted an 18 year study on the effects of overfishing on coral reefs off the coast of Kenya. The study found that large scale commercial fishing gave rise to an explosion in sea urchin populations, which destroy coral algae that is essential for coral growth and survival. In contrast, areas unaffected by commercial fishing had lower populations of sea urchins and as a result, had higher growth rates.

Unsustainable Tourism

Poorly managed tourism in some coral regions, particularly in Southeast Asia, is responsible for significant coral degradation and bleaching. Over 80% of the coral reefs in Southeast Asia are considered at risk due to overdevelopment of coastal areas and the development of tourist resorts on top of reefs. Some resorts empty their sewage into the ocean, causing an increase in water acidity which directly impacts on a reef’s ecology. Careless diving, particularly when tourists touch reefs and take pieces of coral as souvenirs, permanently damages corals. Divers and tourists can also stir up sediment in reefs, contributing to coral bleaching.

Sedimentation

Construction along coastal regions, mining, agriculture, deforestation, dredging, tourism, logging and industry create sediment runoff which seeps into coastal rivers and estuaries. Sediment particles travel from rivers into the sea and into coral reef areas, depriving coral of the light it needs to survive. High rates of sedimentation have been demonstrated to lead to coral bleaching, which in turn affects species that rely on coral reefs for survival. Mangrove trees, found in the tropics and subtropics, act as sediment barriers, by filtering sediment before it reaches the ocean. However, deforestation of mangrove trees for firewood and for land clearance is allowing excess sediment into the oceans and into coral reef regions.

(CC) Image by Toby Hudson

(CC) Image by Nick Hobgood

(CC) Image by travelinknu

Image by National Park Service

(CC) Image by Shahnoor Habib Munmun

Action

One of the most vital steps needed to help protect coral reefs is the creation of marine reserves to ensure corals are safe from further human-induced effects. Recognising the importance of The Great Barrier Reef for thousands of marine species, The Australian government currently protects 33% of it in a marine reserve. Other governments need to follow the example of Australia and must recognise the importance of coral reefs as they contain around 25% of all marine species. Urging governments and decision makers to push for greater protection of reefs will help ensure they survive for many years to come. By not purchasing any item that comes from a coral reef including shells, dead corals, starfish souvenirs or sponges you can help reduce the number of marine species being taken from their reef homes. If diving or snorkelling in a coral reef region, please ensure you never touch the coral or remove any parts of a reef.