Coral Reefs

Coral Reefs in Danger

Coral Reef
A school of Anthias swimming over tropical coral reef with healthy hard coral gardens with Staghorn coral in Komodo National Park, Indonesia. Jeff Hunter/Getty Images

Coral reefs are physical formations primarily comprised of corals which are small invertebrate marine animals. An individual coral, also called a polyp, is cylindrically shaped with an exoskeleton. The exoskeletons give each polyp a hard rock-like outer body and a sac-like inner body. Chemically, corals secrete calcium carbonate from their bodies, which form their exoskeletons. Since corals remain immobile individual polyps cluster together and form colonies, which allow them to secrete calcium carbonate and form coral reefs.

The coral reefs attract algae, which aid coral by producing food. In turn, the algae receive shelter by the coral. Living corals and algae form closest to the water's surface on top of older, deceased corals. The corals secrete limestone during their life cycle, which helps reefs expand in area. Since reefs need algae to survive most form in calm, shallow, clear waters, and thrive on sunlight. They form in the waters fed by warm oceanic currents which largely limits their extent to no more than 30 degrees north and south latitude. Other marine life develop along reefs, making them among the most diverse ecosystems in the world. Altogether coral reefs attract nearly a quarter of the world's ocean species.

Types of Coral Reefs

Some coral reefs can take thousands of years to form. During their formation they can develop into several different shapes depending on their location and surrounding geologic features.

Fringing reefs are comprised of platform-like coral rock.

They are usually either connected to the mainland or very close to the shore, separated by a semi-enclosed lagoon where deeper water lies.

Barrier reefs form close to the shoreline but are not connected like fringing reefs. A wider semi-enclosed lagoon forms between the reef and shore where coral cannot grow due to ocean depth.

Barrier reefs also sometimes extend above the water's surface, which can often hinder navigation.

Atolls are circular shaped reefs that completely enclose a lagoon. Lagoons within atolls are more brackish than the surrounding sea water and often attract fewer species types than the surrounding coral reef due to the higher salinity.

Patch reefs form on shallow patches of the seabed separated by deeper water from nearby fringing reefs and barrier reefs.

Functions of Coral Reefs

Coral reefs have several different functions. Coral reefs help prevent sediments from washing up and damaging the shoreline. They act as a physical barrier which helps create a healthier, protected coastline habitat. They also sequester carbon dioxide, which helps create an environment that continues to attract marine biodiversity. Coral reefs also have economic benefits for nearby cities and towns. Coral can be harvested for use in medicines and jewelery. Fish and marine plants can be harvested for use in aquariums worldwide. Tourists may also visit to view the spectacular underwater life of coral reefs.

Environmental Threats to Coral Reefs

Many coral reefs have experienced a phenomenon known as bleaching, where corals turn white and die after expelling the algae that helped support them.
Bleached coral grows weak and eventually dies, which causes the entire reef to die. The exact cause of bleaching remains unclear, though scientists predict it may be directly related to sea temperature changes. Global climate events such as El Nino and global climate change have raised sea temperatures. After the El Nino event in 1998 approximately 30% of coral reefs had been lost permanently by the end of 2000.

Sedimentation also poses a threat to coral reefs worldwide. Though reefs only form in clear, sediment-free waters, soil erosion due to mining, agriculture and forestry causes rivers and streams to carry sediment to the sea. Natural vegetation such as mangrove trees live along waterways and shorelines remove sediments from water. Loss of habitat due to construction and development increases the amounts of sediment in the sea.

Pesticides also make their way into the sea through crop field runoff, which increases the amount of nitrogen in the sea, causing corals to grow weak and die. Careless management practices such as overfishing and extensive coral mining also disrupt coral reef ecosystems.

Coral Reef Conservation and Regeneration

One proposal to help save coral reefs is to tend to them as one would a garden. Introducing plants to remove sediment and algal overgrowth can help temporarily keep coral reef ecosystems in balance. Increasing efforts to reduce pesticide runoff from crop fields can also help reduce nitrogen levels in the sea. Reducing carbon dioxide emissions from human activities can also help improve overall coral reef health.

Programs specifically targeted to locally improve reef health have also been created. The Coral Gardens Initiative was a non-governmental organization's approach to manage resources and help conserve reefs in the southern Pacific Ocean. Existing management capacities were reviewed to determine the effectiveness of the practices. Any gaps were identified so that they could be improved upon. Building and improving management capacities were stressed along with training people to continue and facilitate information exchanges. The project's approach empowered local residents to change their land management techniques that would have a greater impact on their local ecosystems. Conserving and regenerating existing reefs remain the best approach to keeping coral reef ecosystems healthy and thriving in the future.