A swim in a tropical stream, Corcovado Natl Park.
Coral reefs are ocean habitats that are warm, clear, shallow and rich in life. Coral reefs cover less than one percent of the earth’s surface, however they are the most diverse and oldest marine ecosystem on earth. Coral reefs have many benefits that affect communities at the local and national level. For example they provide protection, medicinal benefits; in addition they provide many economic benefits in the form of tourism dollars. Corals and other species that secrete calcium carbonate construct coral reefs. Corals are actually little plant-like animals, which build a coral skeleton that eventually forms the complex structures that we call coral reefs. These corals are composed of tiny cells of algae (zooxanthellae) that work in a symbiotic relationship with the coral polyps to convert sunlight and other nutrients into energy, which facilitates in coral growth and production. Reefs are formed when coral polyps die and leave behind a hard, stony structure made of limestone.
Coral reefs are found worldwide but are concentrated around the equator. Many coral reefs are found in shallow waters. Coral reefs house thousands of fish as well as crustaceans, sea turtles, mollusks, jellyfish, anemones, sea stars and many other marine species that are found nowhere else on earth. Individual coral colonies may be up to 1000 years old. Since these habitats are so diverse and house many species they are often referred to as the “rain forests of the sea”. In the United States coral reefs sustain a multibillion-dollar industry in the form of tourism annually. Unfortunately coral reefs are depleting at an alarming rate. Already 27% of the world’s coral reefs are gone and if the current trends continue then it is estimated that another two thirds will be lost in the next 30 years. Coral development takes a long time, in one year corals can grow about 1 cm. It could take up to 500 years to recover a 5-meter stretch of coral
Since corals are plant-like animals they depend greatly on sunlight and therefore require clear water for growth and production. The health of the coral reef depends on a delicate balance of sunlight, stable salinity, and water temperature. Clear water along with the shallow depth allows sunlight in to work with the symbiotic algae within the coral. The algae photosynthesize an produce valuable nutrients that are needed by both organisms. A gentle wave action is also needed in order to remove sediment from coral reefs, without the gentle movement corals would suffocate and starve. The wave action also brings in a large supply of planktonic organisms that feed the coral.
There are two main types of coral: hard and soft coral. Hard corals have hard limestone skeletons that form the basis of coral reefs. Soft corals do not actually build reefs. Soft corals look like colorful plants or trees; soft corals do not possess the zooxanthellae (algae) but do produce a small amount of calcium carbonate to help them maintain their shape. Since soft corals do not possess the symbiotic algae they can live in other places besides clear shallow warm water, for instance soft corals can also be found in cool dark deep waters. You can easily distinguish between soft coral polyps and hard coral polyps because soft coral polyps have eight tentacles and hard coral polyps have multiples of six tentacles.
Even thought hard corals are know as the reef builders, they are still fragile and can be damaged or even destroyed by cyclones or by boat anchors. Corals are found in many oceans but the hard corals that build reefs are only found in the tropical and subtropical areas. The major reef-building corals are brain corals, small and large star corals, finger corals, elkhorn corals, staghorn corals and the plate corals.
Elkhorn or Staghorn have the same branching shape that can be found in a variety of colors ranging from pastels to bright green, blue and orange. Most of them are think dense branches that grow faster than other hard corals. These types of corals are mainly found in shallow waters. Boulder corals are massive and are the base of the reef. Boulders are often the largest of the rocky outcrops on the coral reefs. This type of coral can exhibit many different growth patterns including but not limited to mountains, domes, boulders, multi-lobed heads or knobs. Foliate or leaf corals like the name implies actual look like giant leaves or a cutting from a plant with very thin walls. These colonies are very fragile and they can be the dominant type of coral in shallow water reefs. Brain corals exist in a variety of colors including shades of green, pink, red, blue, or brown and are often found with an iridescent sheen. As their names imply these corals have large groves that resemble a brain. The shape of a brain coral is spherical or hemispherical. Pillar corals as their name implies resemble large dense cylinders. Pillar coral is different from all other types of hard corals because they feed during the day. Pillars can reach heights of up to 10 feet tall. This type of coral shares many of the same similarities as the Elkhorn or Staghorn.
Soft corals are different from hard corals because some do not contain the algae (zooxanthellae), which helps the hard coral build its calcium carbonate skeleton. Hard corals need to be in very clear shallow water in order to receive the amount of sunlight that is need for the algae to photosynthesize. Soft corals can be found in more diverse environments than the hard corals because of the lack of dependence on the algae. Soft corals come in a larger variety of colors than the hard colors, and most of the time they are associated with poisonous chemicals that are designed to discourage other coral growth and predation by fish. You need to look at a soft coral more closely to notice some of the features that differentiate them from hard corals. In addition to having a different number of tentacles the tentacles on the soft corals have a feathery appearance.
A prime example of a soft coral is a sea fan. Sea fan can grow up to several feet across and are usually found in strong currents. Sponges are another example of a soft coral. Sponges actually filter the water in the reef, like their counterparts that we use to bathe with they can absorb up to 30,000 times their body volume each day. Sponges also hold the promise of medical benefits. The compounds found in these soft corals are being explored by researchers to determine their medicinal properties.
Coral reefs are found mainly in shallow, warm, sunny regions between the Tropics of Cancer and Capricorn. They usually only extend further north or south where there are warm currents. They usually develop near land and most prefer temperatures between 21-30 °C (70-85 °F). Coral reefs can occur at depths up to 100 meters. Coral reefs can be found in over 100 different countries waters, and they cover and estimated 300,000 square kilometers or 110,000 square miles. The majorities of the world’s coral reefs lie within the waters of developing nations, and consequentially support millions of people through seafood, tourism, and medicinal products. In addition to the monetary benefits reefs also provide shoreline protection from storms and erosion. Unfortunately, the reefs are being destroyed at rapid rates and we stand to lose much more than monetary benefits we could lose biodiversity because the coral reef are considered biodiversity hotspots.
There are many threats to coral reefs and the majority of them are human induced. Coral reefs are particularly susceptible to human activities because most coral reefs occur in shallow waters that are near shores where human impacts are the greatest. Human impacts such as population stress, increased sediment load, shipping, development along shorelines, over-fishing, habitat destruction, pollution, careless tourism, and ocean warming and bleaching have dramatic negative impacts on the coral reefs. Natural disasters such as hurricanes and earthquakes have significant effects on the coral reef ecosystem however the damage is considered a natural cycle of the ecosystem. Human damage has a more significant effect on the coral ecosystem and it can take a much longer time for the reef to recover.
Human practices such as the use of dynamite or poison capture have lead to over-fishing as well as enormous damage to the coral reefs. The reefs are so fragile that even an inadvertent touch by a diver or snorkeler can severely damage the coral polyps. Pollution especially siltation from land-based construction, and fertilizer runoff have lead to coral reefs destruction worldwide not just in the United States. The sedimentation clouds the water and blocks the sunlight required for photosynthesis by the symbiotic algae. Hard corals are very dependent on the zooxanthellae algae and the relationship is being threatened by global warming. Global warming increases sea temperatures and therefore puts the delicate symbiotic relationship in jeopardy.
Water pollution is has been identified as one of the primary causes of coral reef degradation. Pollution comes from a variety of sources and is often hard to trace to one particular source. Oil, gas, and pesticides are poisons to the marine and coral life. Water pollution comes from humans, animal waste and/or fertilizers that are dumped directly into the ocean or river systems. Hence, there are increased amounts of nitrogen and phosphorus that are added to the ecosystem. As a result algae grows out of control and the reefs are smothered because the sunlight is cut off. Pollution comes in several forms. Trash in the oceans also contributes to the destruction of the reefs by blocking sunlight. Trash is also very damaging to the marine life that lives in the coral reef. Sea turtles can mistaken plastic bags for jellyfish and accidentally eat them, which will eventually cause the turtle to starve to death. Discarded fishing nets snag on reefs and literally strangle thousands of fish and other marine life.
Sedimentation tends to have similar effects as water pollution. Sedimentation is a result of construction and deforestation along costs and inshore construction, mining, logging and farming. All these processes lead to erosion, which results in sediment overloading in ocean ecosystems. The sedimentation blankets coral reefs and actually smothers the coral because it deprives the corals of sunlight for photosynthesis. Some natural marine ecosystems include mangrove trees and sea grass beds. These are vital aspects of the marine ecosystem because the trees and grasses act as filters for sediment. Unfortunately these natural filters are being destroyed at alarming rates as well, which has lead to an increase in the amount of sediment that reaches the reefs.
Development along the coast along with an increased population that goes along with it has put great pressure on our coastal resources. In some drastic cases piers as well as other structures even airports have been built directly on top of coral reefs. At one point in time large cities like Hong Kong, Honolulu, and Singapore use to have flourishing coral reefs. Dredging in harbors and shipping pressures have also lead to the destruction of the coral reefs. In some areas corals are mined for there construction materials that are eventually made into cement. Pieces of coral are often removed for the sole purpose for use as bricks or road-fill. Coral are often removed for other reasons than construction purposes. Coral is frequently sold as souvenirs or jewelry.
Many of our current fishing practices are very destructive and very unsustainable. Some of the more popular fishing techniques include cyanide fishing and blast fishing. Cyanide fishing supplies live fish however the technique requires the fisherman/woman to squirt the poison into the reef in order to stun fish. The cyanide actually poisons the coral polyps. Another destructive fishing practice is over-fishing where too many fish are taken from the reef. This is often a result of a large population in an area were the people are extremely dependent on the reef for survival. In some areas people even use explosives to blast apart the coral in order to fish.
Careless tourism is another leading cause of coral reef destruction. Some resorts empty their sewage into fragile waters that surround coral reefs. Even wastes kept in septic tanks can leak out into surrounding waters. The sewage pollutes the reef waters but it also promotes algal growth, which block sunlight. Recreational activities associated with tropical locations can also lead to coral reef damage. Activities such as boating, diving, snorkeling and fishing have significant effects. Walking near coral reefs would be enough to stir up sediments, which would contribute to coral reef destruction by blocking valuable sunlight. When boating or fishing people accidentally harm reefs by dropping anchors directly on the reef. Some tourists collect the corals and don’t even realize the damage they are causing to the coral reef.
Ocean warming could be due to greenhouse gas build up, which is a result of trapped solar radiation. Mass coral bleaching has also been linked to increased water temperatures. The increased heat or ultraviolet radiation can cause coral polyps to eject the zooxanthellae algae that live within them. The algae can provide up to 80% of the energy that corals need. The majority of the time the algae are also responsible for the color of the coral. Therefore when the temperatures rise and the algae leave the coral the coral can appear white or “bleached”. Corals can come back from bleaching but human pressures often prevent coral colonies from recovery.
Indirect human influences are the most damaging to the coral reefs. Shoreline construction and deforestation release sediments into the ocean directly or indirectly through stream and rivers. The sediments smother the corals by blocking the photosynthesizing algae. Nutrient rich algal blooms form from fertilizer runoff. In addition hot-water discharge from industrial plants poisons coral communities.
Should we be concerned about the destruction of our coral reefs? Of course we should, coral reefs have many benefits including housing the second most diverse group of organisms on earth, providing pharmaceutical products, economic and educational benefits of tourism, all while buffering local communities.
Well-developed reefs contain thousands of years of history. Since the reefs last so long and contain so much history they are an important part of many cultures, in many cases they hold the natural heritage of the area. Coral reefs house almost a million fish and other marine species and many of these species are needed for survival in certain areas. In many areas the reefs are the sole source of protein. Reefs contain more species of fish than anywhere else in the sea, it is estimated that 25% of all know marine species find shelter in coral reefs. Reefs house over 4,000 species of fish, 700 species of coral and thousands of other plant and animal life.
Coral reefs are the second most diverse ecosystem, second only to the tropical rainforests. Sadly the biodiversity that is found within the coral reef community is rapidly depleting. This rapid deterioration in such a diverse region is why many of the coral reef communities found around the world are considered biodiversity hotspots. There are many marine species that are found only in coral reefs and nowhere else on earth.
Coral reefs have often been called the medicine cabinets of the sea. Reefs hold the possibility of cures for cancer, human bacterial infections, arthritis, viruses and other diseases. Out of a possible nine million reef species only one million have actually been identified. There are many drugs that have already been developed from coral reefs one of the most famous is AZT, which is a treatment that is used for people infected with HIV. The AZT is based on chemicals that come from a Caribbean reef sponge. Other compounds that have been extracted from coral reefs have been used as treatments for cardiovascular diseases, ulcers, leukemia and skin cancer. Coral has even been used as a bone grafting material. Surprisingly marine organisms are the focus of more than half of all the new cancer drug research.
Many countries depend on coral reefs as their main source of income. On average countries that have coral reefs within their waters generate more than half of their gross national product from the reefs. Every year tens of millions of tourists dive or snorkel on coral reefs worldwide. In Caribbean countries most of their foreign earnings come from tourism, and fees that are by paid by tourist to support marine parks. Reef tourism in the Florida Keys generates an estimated $1.6 billion dollar a year. People that depend on tourism in coral reefs areas are significantly affected by reef destruction. One of the biggest benefits of the coral reefs is the fact that they provide protect to shoreline communities from storms, wave damage, and erosion. When coral was mined away in Maldives, the protection replacement wall cost approximately $10 million dollars a kilometer.
Despite all the extraordinary value that coral reefs provide they are extremely threatened by human activities. Currently 25% of all the coral reefs in the world have been severely destroyed and without drastic global conservation the outlook is bleak. In 2000 NOAA along with other federal agencies and coastal states and territories came up with the U.S. National Plan to Conserve Coral Reefs. The aim of the project is to understand coral reefs and reduce the adverse impacts of human activities. Currently digital maps of coral reefs are being made to make a monitoring system that would track the health of the U.S. coral reefs. Reefs only cover less than one percent of the ocean floor but support approximately 25 percent of all marine species. Even with the concentration of coral reefs in the tropics people beyond the boundaries of the reefs benefit.
United States Coral Reef Task Force. http://www.coralreef.noaa.gov/ 2003.
Bohnsack, J. A. (1996). “The impacts of fishing on coral reefs.” Biological Conservation 76(2): 211.
Edinger, E. N. R., Michael J. (2000). “Reef classification by coral morphology predicts coral reef conservation value.” Biological Conservation 92(1): 1-13.
Grenfell, A. M., Spalding, M.D. (1997). “New estimates of global and regional coral reef areas.” Coral Reef 16(4): 225-230.
Hernandez, G. (2003). Coral Reef, NOAA. http://coralreef.gov/ 2003.
Hodgson, G. (1999). “A Global Assessment of Human Effects on Coral Reefs.” Marine Pollution Bulletin 38(5): 345-355.
Hoffmann, T. C. (2002). “Coral reef health and effects of socio-economic factors in Fiji and Cook Islands.” Marine Pollution Bulletin 44(11): 1281-1293.
McClanahan, T. R., Obura, D. (1997). “Sedimentation effects on shallow coral communities in Kenya.” Journal of Experimental Marine Biology and Ecology 209(1-2): 103-122.
McClanahan, T. R. (2000). “Bleaching Damage and Recovery Potential of Maldivian Coral Reefs.” Marine Pollution Bulletin 40(7): 587-597.
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