Coral Reefs and the Crown-of-Thorns Starfish (Final)
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A swim in a tropical stream, Corcovado Natl Park.
Dr. Hayes Cummins
The Crown of Thorns Starfish and the Coral Reefs
Belonging to the phylum Echinodermata, the crown-of-thorns starfish, Acanthaster planci, is a radial marine animal (Kosarek). It is related to sea urchins, sea lilies and sea cucumbers. Adults have 16-18 arms with poisonous spines. The Crown of thorns (COTS) is the only poisonous starfish. They are multi-colored with thousands of 4-5 cm sharp poisonous spines, in fact it got itŐs name from the long sharp spines all over itsŐ body. They may grow very large, up to 80 cm, but the average size is about 25-35cm (Sikorski). The Crown of thorns starfish cannot swim and is able to move around due to its tiny tubular feet located in the groove under each of it many arms.
They play a major role in the destruction of tropical coral reefs. Many of the worldŐs coral reefs have been infested with these starfish that eat all of the living coral. The COTS feeds mainly on the tabular coral species, Acropora specifically and coral polyps. They do not eat brain coral, algae, clams, sea anemones, or each other, but when the starfish become overpopulated and desperate for food they will eat less desirable corals. They can eat up to their body size in coral each day, causing the rapid decline of the coral population on the reefs. In some cases, coral cover can drop from 25-45% down to 1% in just 2-3 seasons (Sikorski). The COTS has a very unique way of eating the coral, they position themselves over a piece of coral and they release their stomach out of their mouth and spread its stomach over the fresh hard coral. It then secretes digestive juices which dissolve the soft fleshy layer of the coral (Bradbury). Finally, it digests the underlying coral tissue and leaves a white coral skeleton. The digestive juices are very toxic and contain a chemical called saponin that harms marine organisms and humans (Kosarek). It is feared that COT will destroy the structure of the coral reef and it will never fully recover.
The Crown of Thorns starfish spawns from December to April when the water temperature is about 82˚F. Acanthaster planci reproduce sexually. Sexes are separate and the timing of egg and sperm release is fairly simultaneous, therefore fertilization is external. Once an egg is fertilized in the water column and develops into a larva and drifts for 2-4 weeks on order to develop. Then the juveniles settle to the sea floor and continue development there, until they are about 6 months old. During that time they are transforming to an adult form, growing arms and spines and continuing to get bigger (Shmid). At 6 months the starfish are 25 cm across and are ready to eat coral. They reach full maturity after 2 years and are ready to breed and start the cycle over again. COTS reproduce very rapidly because each female produces 60 million eggs in a single season, which makes the odds that a large number of eggs will be fertilized very high. Finally after 3- 4 years they starfish enter the senile phase and begin to decline in size and movement (Sikorski). In the late 1970s, new research discovered that an increase in population had occurred earlier, followed by a period of decline in the population, thus showing that the COTS follow their own natural cycle ("crown-of-thorns starfish." Encyclopedia Britannica).
They are found in the Red Sea and Indo-Pacific coral reefs. These starfish are especially abundant in Australia's Great Barrier Reef (Schmid). The COTS prefer to live in deep water and sheltered areas with low water movement. They are also very sensitive to pollutants so they do not live near any highly populated coast. COTS are bottom dwellers who live very sedentary lives; moving slowly along the seafloor in search of food (Perrins).
Beginning about 1963 the COTS population increased enormously on Australia's Great Barrier Reef. The population explosion was attributed to the decimation of its chief predator, a large marine snail, the Pacific triton, by shell collectors. Thereafter, the starfish multiplied throughout the southern Pacific, hitting Hawaii about 1970, destroying the coral reefs and islands (Tellus Consultants Ltd.). Besides the Giant Triton, the COTS have no other predators as an adult. However it is very vulnerable in its early stages and can be eaten by many marine animals in and around the coral reefs, such as shrimp, worms and various reef fish, especially the Humphead wrasse, which feed on larvae or small adults ("crown-of-thorns starfish." Wikipedia). The COTS has 2 defenses against predators. The first and main defense are itsŐ spines, they are very sharp and are capable of pricking and stinging, inflicting great pain that can last for hours ("crown-of-thorns starfish." Wikipedia). The second defense is the saponin chemical that is released when attacked; this chemical is dangerous to humans and marine organisms. For humans it usually affects the feet and hands, causing intense pain, nausea, vomiting, numbness, and black and blue swelling around the puncture, but has also caused death in some cases (Sikorski).
If the Crown of Thorns starfish is not stopped, it will cause many adverse problems for the coral reefs and surrounding areas. This has been an issue on the Great Barrier Reef and other Indo-Pacific reefs for nearly forty years. It is feared that the structure of the reef will be totally destroyed exposing the North Queensland coast to increased levels of wave action and erosion. Coral reef communities may never fully recover if the COTS continue to kill the slow growing corals and having outbreaks every 15 years, not giving the coral a chance to rebound form the last outbreak. In 1988, the Australian Institute of Marine Science initiated a large scale survey program, surveying 228 reefs through out the length of the Great Barrier Reef within one year. They found that 65% of all reefs surveyed were considered to have experienced a recent outbreak of starfish. Almost 86% of reefs currently experiencing an outbreak had moderate to high coral mortality over at least a third of their perimeters (Moran).
There are many future consequences if the COTS if not stopped. There will be a hug loss of tourism if the coral reefs are destroyed and in order to keep the healthy they need costly research and control programs. There will be a loss of coral dwelling organisms causing a negative impact on the local fishing industry. As mentioned before there will be a loss of shoreline protection causing erosion. There will be a loss of medicinal properties available in the corals and a loss of education al benefits provided by the coral reefs.
The coral reefs provided us with a wealth of resources and it would be a shame to lose them. They are a huge money earner for lower-income countries through exploitation of their resources and through tourism. The coral reefs are also home to one third of all known species of marine fishes and one million species on all. They protect an estimated 155 of all beaches and coastlines from storms and erosion by reducing the action of ocean waves. They are made of polyps that remove carbon dioxide from the atmospheres as part of the carbon cycle. It serves as a tourist attraction and building materials in many parts of the world. Without the coral reefs millions of dollars would be lost as well as hundreds of jobs. In Florida, coral reefs provided $1.6 billion in revenue from recreation uses, in the Caribbean, tourism provides 50% of the GNP (Gross National Product). In Thailand 5,000 small boat and dive shops depend on the reef tourism and on the Great Barrier Reef, tourism produces $1.4 billion in revenue (Sikorski). Without the reefs many of these countries would be struggling and be living in even more poverty.
The big question is, Ňwhat do we do about the Crown of Thorns starfish?Ó We cannot just leave it up to nature, because there is a flaw in the cycle. The COTS only has one predator as an adult, known as the Pacific Triton Shell. However, the Pacific Triton has been over fished, and the population is currently so low that they have little effect on controlling the Crown of Thorns population (Tellus Consultants Ltd.).
In order to control the population marine biologists and scientists have come up with a few solutions. They can go to each coral reef and inject every starfish with a concentrated solution of copper sulfate or by injection with formaldehyde ("crown-of-thorns starfish." Encyclopedia Britannica). However that is very costly and time consuming and since the starfish reproduce so rapidly it is very difficult to get them under control, while other COTS are simply removed from the reefs and destroyed. These two methods are very costly. It costs millions of dollars in order to keep small areas of the reefs under control. The cost of killing 3,100 crown of thorns starfish in $54,000, and that only covers ¸ of a square kilometer (Sikorski). They have also discovered that using underwater fences can control where the COTS are and can keep then away from the coral reefs. However it also costs a lot of money to buy and lay the fences on the bottom of the ocean, a lot of money that the countries in which it affects the most do not have. Even after the starfish is under control it will take over ten years for the coral reef to recover and return to its original form.
The Crown of Thorns starfish is a huge problem that needs to be solved but at the time there is no reasonable way of controlling the outbreaks. Coral reefs are the most beautiful and most abundant natural habitats that need to be saved from the wasteland that it will become, if the crown of thorns attack invades. Luckily, the Crown of thorns has not been found in the Atlantic Ocean and has not affected the Florida coral reefs, but we need to stay alert and watch for outbreaks, in order to keep them under control or completely out of the reefs.
1.) Bradbury, Dr. Roger. "The eating habits of Crown-of-Thorns starfish." Everything2. 01 Oct 2002. 25 May 2006 .
2.)"crown-of-thorns starfish." Encyclopedia Britannica. 2006. Encyclopedia Britannica Premium Service. 30 May 2006 .
3.) "Crown-of-thorns starfish." Wikipedia. Wikipedia, 2005. Answers.com 25 Mar. 2006. http://www.answers.com/topic/crown-of-thorns-starfish
4.) Kosarek, N. 2000. "Acanthaster planci" (On-line), Animal Diversity Web. Accessed 22 May, 2006 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Acanthaster_planci.html.
5.) Moran, P. J. , R. H. Bradbury , and R. E. Reichelt. Australian Institute of Marine Science, P.M.B. No. 3, 4810 Townsville M.C., Australia.
6.)Perrins, C., A. M.. 1985. Spiny-skinned Invertebrates. The Encyclopedia of Aquatic Life. Oxford: Equinox Ltd..
7.) Schmid, H. 1998. The Crown-of-Thorns Starfish. Ocean Realm, Spring: 29-31.
8.) Sikorski, Janelle. "Topics in Oceanography." Shideler Hall, Oxford, OH. 20 Apr 2006.
9.) Tellus Consultants Ltd., "Out of Control." Community Environmental Research in the Pacific Islands. 22 May 2006 .
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