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Example research essay topic: Crown Of Thorns Coral Reefs - 3,746 words

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Coral reefs are among the most varied and productive communities on Earth. They are found in the warm, clear, shallow waters of tropical oceans worldwide. Reefs have functions from providing food and shelter to fish and invertebrates to protecting the shore from erosion. Unfortunately, as our understanding of corals and coral reefs increases, it becomes apparent that the effects of the human population on these communities may be increasing as well. Reef-building (or hermatypic) corals are of the order Scleractinia in the classAnthozoa of the phylum Cnidaria.

About 6, 000 species of Anthozoans exist, all of them marine (Pechenik 1991). Coral reefs of the western Pacific are much more different than those of the Atlantic and Caribbean. There are up to 75 % more genera and 85 % more species of corals in Pacific waters (Wilkinson 1987). Reefs are formed by calcium carbonate produced by tiny coral polyps. Corals are not the only builders and.

the chief architects of reef structure. Coralline algae connect various corals together with compounds of calcium, and other organisms such as tube worms and molluscs give their hard skeletons (Cousteau 1985). These organisms create many different types of reefs. Reefs are important land builders in tropical areas, forming islands and altering continental shorelines (Goreau et al. 1979). A coral colony may consist of thousands of polyps. Polyps are carnivorous, feeding on small particles floating in the water.

However, endo symbiotic algae known aszooxanthellae provide important sources of nutrition to hermatypic corals (Rowan and Powers 1991). Corals reproduce both sexually and asexually. Amazingly, an entire colony many meters in diameter can start out as a single polyp. Because many coral reef organisms can put up with only a narrow range of environmental conditions, reefs are sensitive to damage from environmental changes (Richmond 1993). Corals are open to diseases and bleaching.

Natural events such as hurricanes can damage coral reefs as well. In addition, many problems to reefs are human caused. Because of the important ecological and economic roles coral reef communities fulfill, an understanding of the stresses and dangers to the reefs is necessary. Fortunately, many of the human caused hazards to coral reefs can be resolved (Richmond 1993). Coral reefs consist of many different species of corals. These corals are made up tiny organisms called polyps.

The structure of the polyps and the skeleton of the cialis a simple combination. A polyp is made up or two cell layers: the epidermis and the gastro dermis. The non-tissue layer between the gastro dermis and the epidermis is called the mesoglea. The polyp contains mesentery filaments, which contain nematocysts used in food capture, a pharynx, endothelial dissepiment's (horizontal layers of skeletal material) andthe columella (the central axis of the corallite found below the mouth). The corallite issue part of the skeleton deposited by one polyp. The skeletal wall around each polyp is called the theca.

Other structures include the calice (the upper opening of the corallite), the coenosarc (the coral tissue that stretches over the surface of the coral between the polyps), the coenosteum (the skeletal material around the corallite's), and the coral lum, which is the skeleton of the coral. The coral anatomy also includes calcareous plate-like structure known as septa. The septa radiate from the wall to the center of the corallite. There are two types of septa: insert septa which lie below the corallite wall and exsert septa which protrude above the corallite wall. Corals are of two types: perforate and imperforate.

Perforate corals have porous skeletons with connections between the polyps through the skeleton. Imperforate corals have solid skeletons. Many corals have different growth forms. They can be placid as in Tubastreacoccinea (orange cup coral) and Favia fraud (golf ball coral).

They can also bemean droid in which corallite's form a series within the same walls, as in the speciesDendrogyra cylinders (pillar coral). Other growth forms include concord, spherical shaped and phalecoid, as in Eusmilia fastigiate. There are three basic kinds of coral reefs in the Caribbean: fringing reefs, barrier reefs and atolls. Fringing reefs are coral reefs that grow in shallow waters and border the coast closely or are separated from it by a narrow stretch of water. Fringing reefs consists several zones that are characterized by their depth, the structure of the reef, and its plant and animal communities. These regions include the reef crest (the part of the reef the waves break over), the fore reef (the region of medium energy), and the spur and groove or buttress zone (the region of coral growth which includes rows of corals with sandy canyons or passages between each row).

Barrier reefs are reefs that are isolated from land by a lagoon. These reefs grow parallel to the coast and are large and continuous. Barrier reefs also include regions of coral formation that include the zones found in fringing reefs along with patch reefs (small reefs), back reefs (the shoreward side of the reef), as well as bank reefs (reefs that occur on deep bottom irregularities). Coral reefs also include reef flats (the are of the reef not exposed), the reef crest, which runs parallel to the coast and is protected from waves, and a coral terrace (a slope of sand with isolated coral peaks). These features are followed by another coral terrace and a vertical drop into deeper waters. The third typeof coral reefs are atolls.

Atolls are round reefs that develop at or near the surface of the sea when islands that are surrounded by reefs declines. Atolls separate ancestral lagoon and are circular or sub-circular. There are two types of atolls: deep sea atolls that rise from deep sea and those found on the continental shelf. Corals can obtain food in a variety of ways. Reef-building corals rely on the photosynthetic products of zooxanthellae for the majority of their nutrients. However, corals also capture zooplankton for food.

Corals are suspension feeders. They utilize twain methods of prey capture: nematocyst adhesion and mucus entrapment (Sebens and Johnson, 1991). Nematocysts on the tentacles and mesentarial filaments can be used testing prey and move it into the mouth. Some corals will trap prey in sticky mucus on their tentacles and move the prey into the mouth using the mucus and cilia. Prey size is correlated to polyp size (Sebens and Johnson, 1991). Most corals feed at night.

This maybe because night is when the zooplankton travel into the water column and become available for capture. Keeping the tentacles retracted during the day may also help corals avoid predation, protect themselves from UV light, and avoid shading theirzooxanthellae. Prey can be brought into contact with the tentacles by direct interception (the flow of water makes the particles impact the tentacles), by inertial impaction (momentum of dense particles makes them turn aside from the water flow and impact the tentacles), and by gravitational deposition (gravity causes heavy particles to fall into the tentacles) (Sebens and Johnson, 1991). Regardless of the method of capture, prey is moved through the mouth, down the pharynx (gullet), to the gastrovascular cavity for digestion. Corals exhibit sexual and asexual reproduction. The coral colony enlarges in size budding.

Budding may be intra tentacular, in which the new bud forms from the oral discs of the old polyp, as in Diploma, or extra tentacular in which the new polyp forms from the base of the old polyp, as in Montastraea cavern osa. A common type of asexual reproduction in corals is by fragmentation. Broken pieces of corals that land on a suitable substrate may begin growing and produce a new colony. This type of reproduction is common in branching corals like Acroporacervicornis. Many coral species mass spawn. Within a 24 hour period, all the corals fremont species and often within a genus release their eggs and sperm at the same time.

This occurs in related species of Montastraea, and in other genera such as Montipora, Platygra, Favia, and Favorites (Wallace, 1994). In some Montastraea and Acropora species, the eggs and sperm are released in a sack. They float to the surface where they separate and fertilization takes place. Intra species is common but mass spawning raises the possibility of hybridization by congeneric species (Wallace, 1994). The zygote develops into larvae called planula which attaches itself to a suitable substrate and grows into anew colony. Some species of coral brood their larvae.

The sperm fertilizes the egg before both are released from the coral. The larvae float to the top, settle, and become another colony. Species of Acropora release brooded larvae. Four coral conditions have been identified as diseases: white band disease (WBD), black band disease (BBD), bacterial infection, and shut down reaction (Richmond 1993). They are also vulnerable to tumors and parasitic worms.

These maladies are all stress related, and anthropogenic stresses can increase a corals susceptibility to these diseases. Diseases such as BBD and WBD actually kill coral tissue while progressing in and around the coral and leaving the white coral skeleton behind. Edmunds (1991) stated that BBD, caused by cyanophyte Phormidium corallyticum, may have a role in maintaining coral variety because it is most prevalent in coral species that form large colonies and provide a structural framework for the reef. When BBD kills part of these colonies, the skeleton is available to be colonized by other coral species recruits. However, after 25 months, there were not coral recruits among corals infected by BBD (Edmunds 1991). WBD has much of the same effect on corals, leaving behind a white, lifeless coral skeleton.

Gladfelter (1982) does not see WBD as being beneficial to reefs. He feels that WBD destroys the reef structure because the dead coral skeleton brought about by the algae is colonized by algae, invertebrates, gastropods, and boring clinic sponges that work to weaken the coral skeletons making them more exposed to breakage during storms. This situation is also probable for BBD. The exact method by which the diseases are transmitted are unknown.

Eventhough healthy corals may get BBD through contact with an infected coral, diseased corals are not collected naturally on the reef and can be separated by great distances. Thus, it is also suggested that BBD can be spread by currents through trichome's that come off infected colonies and land on other colonies (Edmunds 1991). Corals under stress are more likely to be infected, and BBD has a higher rate of infection in warmer water. Thus seasonal temperatures affect the spread of BBD, andale any anthropogenic warming of water temperatures may increase BBD.

BBD was also found to be more abundant near anthropogenic disturbances. However, WBD has not been found to be related to anthropogenic disturbances (Gladfelter 1982). Corals may also be affected by diseases indirectly. Diseases that infect other reef population may affect ecology of corals. In 1993, a newly encountered pathogen was found to affect coralline algae in the Pacific Ocean (Littler and Littler 1995).

This pathogen also leaves the coralline algae skeleton white as it progresses in a orange band, destroying the algae. Coralline algae help the coral reef community by joining togethesand, coral fragments, and other debris into a hard substrate for the establishment of coral colonies and by absorbing wave energy in the outer reef rim that would otherwise erode the shoreline (Littler and Littler 1995). Another disease which caused a Caribbean-wide mortality in the reef dwelling sea urchin Diadem antillarum was also shown to indirectly affect coral reefs (Lessons 1988). The sea urchin functions as both a grazer on algae that can otherwise smother coral and as a bioeroder of corals as it feeds on them (Lessons 1988). Coral bleaching is the whitening of coral colonies due to the loss of symbioticzooxanthellae from the tissues of polyps. This loss exposes the white calcium carbonate skeletons of the coral colony.

Corals naturally lose less than 0. 1 % of their zooxanthellaeduring processes of regulation and replacement (Brown and Ogden, 1993). However, adverse changes in a corals environment can cause an increase in the number ofzooxanthellae lost. There are a number of stresses or environmental changes that may cause bleaching including disease, excess shade, increased levels of ultraviolet radiation, sedimentation, pollution, salinity changes, and increased temperatures. Corals tolerate a narrow temperature range between 25 degrees Celsius and 29 degrees Celsius depending on location.

Corals bleach in response to prolonged temperature change and not due to rapidly fluctuating temperatures. Lab experiments show that corals bleach when water reaches a constant 32 degrees Celsius (Brown and Ogden, 1993). Experiments have shown that an increase in UV light causes coral bleaching. UV light experienced by corals can increase in calm waters. The amount of mycosporine-like amino acids in a corals tissues helps to determine how much UV it can withstand without bleaching (Gleason, 1993). The exact mechanism by which corals bleach or the trigger that induces bleaching is unknown.

However, there are a number of theories that attempt to answer this question. Laboratory experiments have shown that the zooxanthellae are released into theft of the polyp and then are expelled from the polyp through the mouth (Brown and Ogden, 1993). However, this has not been observed in nature. Another theory is that stressed corals give algae fewer nutrients and thus the algae leave the polyp. Algae may produce oxide toxicity under stress, and these toxins may affect the polyps.

Corals and coral reefs are extremely sensitive. Slight changes in the reef environment may have harmful 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 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 change the landscape, the amount of freshwater runoff increases. This fres-hunter runoff may carry large amounts of sediment farmland-clearing areas, high levels of nutrients from agricultural areas or septic systems, aswell 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 magnify the growth of other reef organisms such as sponges which may out compete the corals forsake 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 decline 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 overfishing, 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 insider 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 audios 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 most healthy 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 thani-fouling bottom paints used by many boats contribute to the formation of toxic concentrations of Tribute 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 place. A.

place 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 tothe drastic effects which A. place 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 protector 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 tothe 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. Coral reefs provide habitats for a large variety of organisms. These organisms region corals as a source of food and shelter. Some organisms that use corals through mutualism, commensalism and parasitism are within the taxonomic groups Porifera, Polychaeta, Gastropoda, Crustacea, Echinodermata and Pisces.

Sponges (Porifera) are found inhabiting cavities in the reef. They remove small chips of calcium carbonate from corals. These sponges, such as China, cause bioerosionin corals. Sponges inhabit corals for the purpose of protection from predators. Polychaetes such as Hermodice caruncular and Gastropods in the familyTrochidae depend on corals for food. They feed on corals such as Porites and Agaricia.

Decapod crustaceans such as shrimps and crabs depend on corals for shelter. Xantidcrabs form cavities in the coral Acropora palate. Fish also depend on corals for protection against predators. One such is the parrot fish (Scaridae). Echinoderms such as Acanthaster place are coral predators. This crown-of-thorns starfish relies on corals fourfold.

There are many other species of fungi, sponges, sea worms, crustaceans and molluscs that bore into coral skeletons. Other organisms that inhabit the coral reefs include sea urchins, jellyfish, oysters, clams, turtles, and sea anemones. Literature Cited Birkeland, C. 1989. The Faustian traits of the Crown-of-Thorns Starfish. American Scientist, 77: 154 - 163.

Brown, B. E. , Open, J. C. 1993. Coral Bleaching. Scientific American, 269: 64 - 70. Cousteau, J.

Y. 1985. The Ocean World. Harry N. Abrams, Inc. , New York, NY, pp. 174 - 175. Edmunds, P. J. 1991.

Extent and Effect of Black Band Disease on a Caribbean Reef. Coral Reefs, 10: 161 - 165. Gladfelter, W. B. 1982.

White Band Disease in Acropora palate: Implications for the Structure and Growth of Shallow Reefs. Bulletin of Marine Science, 32 (2): 639 - 643. Gleason, D. F. 1993. Differential Effects of Ultraviolet Radiation on Green and Brown Morphs of the Caribbean Coral Porites astreoides.

Journal of Limnology and Oceanography, 38 (7): 1452 - 1463. Goreau, T. F. , N. I.

Goreau, and T. J. Goreau. 1979. Corals and Coral Reefs. Scientific American, 241: 124 - 136. Lessons, H.

A. 1988. Mass Mortality of Diodema antillarum in the Caribbean: What Have We learned? . Annual Review of Ecology and Systematics, 19: 371 - 393. Littler, M. M. , D. S.

Littler. 1995. Impact of CLOD Pathogen on Pacific Coral Reefs. Science, 267: 1356 - 1359. Pechenik, J. A. 1991.

Biology of the Invertebrates. Wm. C. Brown Publishers, Dubuque, IA, pp. 91 - 92. Richmond, R. H. 1993.

Coral Reefs: Present Problems and Future Concerns Resulting from Anthropogenic Disturbance. American Zoologist, 33: 524 - 536. Rowan, R. and D. A.

Powers. 1991. A Molecular Genetic Classification of Zooxanthellaeand the Evolution of Animal-Algal Symbioses. Science, Vol. 251: 1348 - 1351. Sebens, K. P. , Johnson, A. S. 1991.

Effects of Water Movement on Prey Capture and Distribution of Reef Corals. Hydrobiologia, 226: 91 - 101. Van Als tyne, K. L. and V. J.

Paul. 1988. The Role of Secondary Metabolites in Marine Ecological Interactions. Proceedings of the 6 th International Coral Reef Symposium, Australia, 1988, Vol. 1. Wallace, C. C. , Willis, B. L. 1994.

Systematics of the Coral Genus Acropora: Implications of New Biological Findings for Species Concepts. Annual Review of Ecology and Systematics, 25: 237 - 262. Wilkinson, C. R. 1987. Inter ocean Differences in Size and Nutrition of Coral Reef Sponge Populations. Science, Vol. 236: 1654 - 1657.


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