Palau Coral Reef.

Palau Coral Reef

Coral reefs are one of the most complex and colorful tropical ecosystems, rivaling rain forests in their richness of life. Coral reef organisms build massive & intricate physical structures that are home to some of the most fascinating plants and animals in the world. Their extraordinary beauty captivates visitors and their productivity provides a wealth of resources for local communities and the world.

What is a coral reef?

Coral reefs are massive structures made of limestone that is deposited by living things. Although thousands of species inhabit coral reefs, only a fraction produce the limestone that builds the reef. The most important reef building organisms are corals.

Coral reefs support over twenty-five percent of all known marine species. As one of the most complex ecosystems on the planet, coral reefs are home to over 4,000 different species of fish, 700 species of coral and thousands of other plants and animals.

A good way to imagine a coral reef is to think of it as a bustling city or community, with the buildings made of coral, and thousands of inhabitants coming and going, carrying out their business. In this sense, a coral reef is like a metropolis under the sea.

What is coral?

Although coral is often mistaken for a rock or a plant, it is actually composed of tiny, fragile animals called coral polyps. When we say "coral" we are actually referring to these animals and the skeletons they leave behind after they die.

Although there are hundreds of different species of corals, they are generally classified as either "hard coral" or "soft coral".

Hard corals grow in colonies and are the architects of coral reefs. They include such species as brain coral and Elkhorn coral. Their skeletons are made out of calcium carbonate (also known as limestone) which is hard and eventually becomes rock. Hard corals are hermatypes or reef-building corals and need tiny algae called zooxanthellae (pronounced zo-zan-THEL-ee) to survive. Generally, when we talk about "coral" we are referring to hard corals.

Soft corals such as sea fingers and sea whips are soft and bendable and often resemble plants or trees. These corals do not have stony skeletons, but instead grow wood-like cores for support and fleshy rinds for protection. They are referred to as ahermatypes or non-reef building corals and they do not always have zooxanthellae. Soft corals are found in both tropical seas and in cool, dark regions.

Where do corals live?

Coral reefs are found in over 100 countries. Most reefs are located between the tropics of Cancer and Capricorn, in places such as the Pacific Ocean, the Indian Ocean, the Caribbean, the Red Sea and the Arabian Gulf. Corals are also found farther from the equator in places where warm currents flow out of the tropics, such as Florida and southern Japan. Worldwide, coral reefs cover an estimated 284,300 square kilometers (110,000 square miles).

Coral reefs grow best in waters with a temperature of between 21 and 29 degrees Celsius (70 ...

This is a preview of the whole essay

Where do corals live?

Coral reefs grow best in waters with a temperature of between 21 and 29 degrees Celsius (70 and 85 degrees Fahrenheit). It is possible for soft corals to grow in hotter and colder places, but growth rates under these conditions are very slow. Corals prefer clear and shallow waters, where lots of sunlight filters through to their symbiotic algae. It is possible to find corals at depths of up to 91 meters (300 feet), but reef-building corals grow poorly below 18-27 meters (60 to 90 feet). Corals also grow poorly near river openings or coastal areas with excessive run-off, because corals need salt water to survive.

Coral reefs occupy less than one quarter of one percent of the earth's marine environment, yet they are home to more than a quarter of all known fish species.

How is a coral reef constructed?

Coral reefs are complex, multi-story structures with holes and crevices shared by various creatures. If a coral reef can be thought of as a metropolis of the sea, then a coral colony can be thought of as an apartment building with many different rooms and hallways that house different marine species. Not all coral species build reefs. The actual architects of coral reefs are hard or stony corals, which are referred to as hermatypic or reef-building corals. As the polyps of stony corals grow, they produce limestone for their skeletons. When they die, their skeletons are left behind and are used as foundations for new polyps, which build new skeletons over the old ones. An actual coral mound or tree is composed of layer upon layer of skeletons covered by a thin layer of living polyps.

Other types of animals and plants also contribute to the structure of the reef. Many types of algae, seaweed, sponge, sediment and even mollusks like giant clams and oysters, add to the architecture of a coral reef. When these organisms die, they also serve as foundations for new corals.

Why is the coral reef important?
Coral reefs deserve protection for their intrinsic natural value. In addition, the economic, tourism, fishing and recreational resources of tropical areas around the world depend upon healthy coral reef ecosystems. Barrier coral reefs protect shorelines from erosion and storm damage. The food, tourism revenue, coastal protection and new medications that reefs provide are worth about $375 billion each year.

Why does the coral reef need protection?
Coral reefs can be damaged by natural processes, such as storms, but they are increasingly at risk from human activities. Coral reef health can be seriously affected and the growth of new colonies hampered by fi ne-grained sediment transported from land into coastal waters as runoff. This sediment runoff can be greatly increased by nearby land developments for agriculture, industry, and housing. Light necessary for photosynthesis by symbiotic algae living in corals is diminished in waters made cloudy or turbid by suspended sediment, reducing coral productivity.

Threats to Coral Reefs

Corals and coral reefs are extremely sensitive. Slight changes in the reef environment may have detrimental effects on the health of entire coral colonies. These changes may be due to a variety of factors, but they generally fall within two categories: natural disturbances and anthropogenic disturbances. Although natural disturbances may cause severe changes in coral communities, anthropogenic disturbances have been linked to the vast majority of decreases in coral cover and general colony health when coral reefs and humans occur together.

One of the greatest threats to coral reefs is human expansion and development. As development continues to alter the landscape, the amount of freshwater runoff increases. This terriginous runoff may carry large amounts of sediment from land-clearing areas, high levels of nutrients from agricultural areas or septic systems, as well as many pollutants such as petroleum products or insecticides. Whether it is direct sedimentation onto the reef or an increase in the turbidity of the water due to eutrophication, decreases in the amounts of light reaching corals may cause bleaching (Brown and Ogden 1993). In addition, increases in the amounts of nutrients enhance the growth of other reef organisms such as sponges which may outcompete the corals for space on crowded reefs.

In addition to runoff, outflows from water treatment plants and large power plants are the cause of much damage to coral reefs. Sewage treatment facilities greatly increase the nutrient levels surrounding their outflow pipes while large power plants alter water temperatures by discharging extremely hot water into the coastal waters. As with all these factors, the basis for the continued degradation of coral reefs is the increasing size of the human population.

As this population increases, so does the harvest of resources from the sea. Due to over fishing, reef fish populations have been greatly decreased in some areas of the world. The removal of large numbers of reef fish has caused the coral reef ecosystems to become unbalanced and allowed more competitive organisms, such as algae, which were once controlled by large fish populations, to become dominant on reefs in many regions.

Due to decreased yields, fishermen have been forced to change their methods in order to catch enough fish to sustain their needs. In some areas this means fish traps with small mesh diameters which catch even the small juvenile fish. In other areas of the world, the use of explosives or poisons has become quite common (Richmond 1993). Not only do these practices kill all fish in the affected areas, but they also severely damage the corals in these areas.

Corals are also very popular as decorations. Often, when people vacation in tropical locations surrounded by beautiful reefs they want to take coral souvenirs home. In order to do this, they either collect pieces of coral themselves or buy pieces from a "curios" shop. These shops receive their corals from commercial collectors who select well developed colonies which will make them the most money. This is very damaging because a large amount of the healthiest corals are selected.

Coral reefs also receive much damage from both commercial and private vessels. The leakage of fuels into the water and the occurrences of spills by large tankers are extremely damaging to local corals. Boat anchors are also very damaging to reefs by breaking and destroying entire colonies. The grounding of large sea-going vessels also results in large sections of coral reefs being destroyed. It has also been found that the anti-fouling bottom paints used by many boats contribute to the formation of toxic concentrations of Tributyl tin and several other chemical compounds which may be harmful to corals or other coral species (Desrosiers, personal communication).

Since most corals mass spawn and produce floating gametes, pollutants and toxins on the surface can effect coral reproduction and development for a large area. Therefore, much care must be taken to reduce or prevent the spillage and leakage of contaminants into the water as well as to improve cleanup procedures of such accidents.

Although much of the coral reefs degradation is directly blamed on human impact, there are several natural disturbances which cause significant damage to coral reefs. The most recognized of these events are hurricanes, or typhoons, which bring large and powerful waves to the tropics. These storm waves cause large corals to break apart and scatter fragments about the reefs. After the storm, these slow growing corals might easily be overgrown by quicker growing algae. In addition, these storms generally bring heavy rain which increases runoff and sedimentation.

Another common threat to coral populations of the Pacific Ocean is the crown-of-thorns, Acanthaster planci. A. planci is a large starfish which feeds on corals by extruding its stomach out onto the coral to digest the living tissue layer (Birkeland 1989). These predators have had serious effects on the coral populations in many regions of the Pacific, and Acanthaster breakouts have been linked to regions of increased development and eutrophication (Birkeland 1989). Many other predators such as fish and gastropods also are known to cause damage to coral colonies, but these generally do not compare to the drastic effects which A. planci has on coral populations.

There are a great number of threats to coral reefs, and most of the threats can be attributed either directly or indirectly to humans. Work must be done quickly to protect our threatened resources. The list of solutions to the many coral reef problems is extensive. These range from better methods of development in order to decrease runoff to the installation of permanent moorings at heavily used anchorage sites. Whatever the solutions, there always needs to be adequate enforcement to ensure proper techniques are being followed. Unfortunately, enforcement has not been great enough in the past and will probably not be in the future. Therefore, the education and cooperation of people throughout the world is necessary if coral reefs are to survive.

By Veenesh Halai