Coral reefs are complex and diverse habitat. They are perhaps on of the most interesting and colorful ecosystems to be found in the marine environment. They are very unique in many ways. Coral reefs play many important poles in the marine world. They must have certain conditions to be formed, and to survive. Lots of different sea life rely on reefs for habitat and sources of food, including some endangered species. Coral reefs are perhaps one of the greatest yet least known of wonders of our world.
The formation of a coral reef is a long and slow process, taking about a year for a reef to grow about half an inch. Many factors affect the growth of the coral. The general pattern of coral reefs is a continuous cycle of growth and destruction, resulting from the growth of the coral and destructive activities of animals and storms. This pattern serves to keep the coral reef alive and at a fairly constant level. Coral reefs must have certain conditions to survive. They must be in reasonably shallow water. Low levels of sedimentation in the water are very important too, because too many sediments in the water can block the sunlight needed for the coral reefs. Because of the sunlight required for reefs to survive, they can only grow to depths of 45 meters deep. They only form in tropical seas and areas that stay above 20 degrees Celsius. The amount of oxygen is also important. Oxygen is produced in the daytime by plant photosynthesis, but the level drops dramatically at night. Ocean waves and water movement play a part in the amount of oxygen in the water as well, this allows diffusion of oxygen into the surface levels.
There are three different kinds of coral reefs. There are fringing, barrier, and atoll. Fringing reefs are attached to margins of an island or continent, rough, table like surface, as much as 1 kilometer wide. On their seaward side they slope steeply to the ocean floor. Fringing reefs grow in shallow water near the shore and prefer dry climates with limited river runoff. There are also barrier reefs, which are similar to fringing but separated from mainland with a lagoon. The number of barrier reefs is greatly increasing due to global warming, because of the rise of the water’s level. Barrier reefs grow best where the land is sinking faster than the water. The most popular barrier reef is the Great Barrier Reef in Australia, which spans over 2,000 kilometers.
The third type of coral reef is the atoll. Atolls consist of a continuous or broken ring of coral reef surrounding a central lagoon. Atolls are unique because they reach to depths of thousands of meters to the ocean floor. This presented a paradox: how can warm, shallow, sunlit water no deeper than 45 meters, create structures that reach thousands of meters to the ocean floor? In 1831, Charles Darwin set out upon the H.M.S. Beagle and circumnavigated the globe. On his journey he came up with a hypothesis on the formulation of coral islands. The essence of his hypothesis was that as a volcanic island slowly sinks, coral reefs form along the sinking flanks of it. Atolls owe their existence to sinking oceanic crust.
Coral reefs are a very important to many different species of sea life. The reefs cover only about 1% of the earth’s surface, yet contain of all of the earth’s species pf fish. Amongst the reefs are complex food webs, and prey relationships. Algae growing on the coral is food for many herbivores. The coral itself is food to many species. The butterfly fish eats individual coral polyps, while the Crown-of-thorns starfish eats entire colonies. A number of species are predators. With all of the dangers of predators in the reefs, there are many different methods of defense, one of which being camouflage. Camouflage is the ability for organisms to change color and appearance to match the environment which they are in, so they are hard to distinguish from their surroundings. Other organisms have distinct coloration that is used as warning predators.
Even some species use chemicals to distract predators. These include chemicals that are toxic, and some that have just a distinctly foul odor that distracts other organisms. There are many interesting forms of sea life found in reefs. Brittle stars are unique to coral reefs. Hence their name, brittle stars break off parts and arms at the slightest hint of danger. They are similar to their sea star friends, but move much quicker. Also found in reefs are Cowries. Cowries are mollusks that are prized by shell collectors because of the various sizes and colors on the shells. There are also many fish that live in coral reefs that show spectacular coloration shapes and intricacies that aren’t found outside the coral environments.
Due to the all of the distinct colors, and unique species, and beautiful sites, coral reefs are extremely popular with divers. Divers do not pose a huge threat to reefs and their environments, but they do pose somewhat of one. Reefs are in danger of many different things. For instance, pollution from all sorts, oil spills being one of the greatest, along with land runoff. Other threats to coral reefs are fishing with dynamite, coral mining, haphazard coastal development, or even over fishing. Scientific reports show that there has been a rapid increase in the damage to reefs in the past 20 years, and scientists have reason to believe that in two more decades, the world’s reefs will decline by 30%. Over half the world’s reefs are in danger of human harm, and 27% are at high risk. The reefs of Southeast Asia, which happen to be the most species diverse reefs in the world, are also in the most danger.
Coral reefs are one of the most interesting things on earth. It is a shame that people know so little about them and that they aren’t taken care of near as well as they should be. They are fascinating to learn about how what they are and what all they do for our environment. There is still some that is unknown about them to us today, and it seems that the best way to find out all that we can about them, is to make it a priority to protect them so they will continue to be around long enough to study.