Endangerment of Coral Reefs
...al amounts of their photosynthetic products" (Sverdrup pg. 465). The zooxanthellae also give the coral the ability to gather the calcium carbonate from the seawater in the column which increases the growth of their calcareous skeletons (Sverdrup pg.465). The polyps extract calcium from the seawater and combine it with the carbon, which is a product of their own respiration, to produce calcium carbonate or limestone. This limestone is secreted layer by layer underneath the colony, which build up a skeleton for the coral. Corals also consume microscopic plants and animals that are in the water column. The microscope plants and animals are known has phytoplankton and zooplankton. There are particles of dead organic matter that floats in the column of water that is usually a white tinted, and refered to marine snow, some corals consume marine snow as well (Castro pg 329). Corals often consume organisms larger then they are such as bottom-dwelling snails and other mollusks. They also consume microscopic plankton such as small shrimp, worms and fish, which are in their larval stage (Sprung pg. 11). All these are components of nutrients that the coral needs and uses to survive and grow. Coral reefs are very sensitive organisms, and if they become too stressed out they become bleached. Bleaching is the whitening of the colonies from the loss of the symbiotic zooxanthellae from the tissues of polyps (Birkeland pg. 8). Although bleaching is normally known in corals, it is not just restricted to them, but it has been displayed by all animals in symbiosis with dinoflagellates algae. It is restricted to benthic animals of the phylum Cnidaria (Douglas). The zooxanthellae are normally golden-brown or a greenish color and give the corals their color. With this loss, it will expose the white calcium carbonate skeletons of the coral colony. Sometimes when corals have become bleached they have a hard time regrowing and if they cannot regrow they will be killed off. Once this has happened it can damage and kill off an entire system of coral reefs (The Science of Climate Change). Even though the corals have become bleached they still are hosting many of the zooxanthellae even though they do have enough to give color, but enough to reestablish the normal numbers of the zooxanthellae when the conditions are better. When the corals have become bleached, they do not grow and become very vulnerable to the environment around them. The corals have many factors, which are mostly environmental changes, that contribute to the process of becoming bleached. Some factors that cause coral to become so stressed out that they release the zooxanthellae from their tissue and become white in color are Salinity changes, sedimentation, excess shade, pollution, diseases, human and animal contact, and increased temperatures of the ocean's waters. In the clear open flowing waters that surround the corals, light can penetrate through the water to bring light to the photosynthetic organisms, zooxanthellae within the tissues of the polyps of the corals, that provide nutrients and food for the corals. A major factor in the bleaching of corals is that they do not get enough light, that there is too much shade covering the top of the waters above them. Seaweed can cause excess shading of the corals, this can be cause by the overgrowth of the seaweed. A reason why the overgrowth of seaweed occurs is that the oceans water had high nutrients within it at a specific time. One way that the waters might have high nutrients is the run off of sewage that is caused the humans, which causes algal blooms. Once the seaweed grows to the point, which it covers the surface of the water and the light cannot penetrate through the water to reach the organisms that use the light to produce the proper nutrients that the corals use. When this happens, the corals do not get enough of the nutrients that allow them to grow. If they do not get the proper lighting to keep the nutrients up to the right levels that is needed they can become bleached because they are being stressed due to the fact that they are not receiving the right amount of nutrients. Another factor that affects the quality of the waters clearness is sedimentation. Sedimentation is when the top or any type of soil, silts that runs off the land and goes into the water columns. There are many different ways that the sediment can reach the open ocean waters and one way is the large amount of run off of sediments through the rivers and from the run off of the land after is has rained. The sedimentation has grown because humans have cut down trees that slow or stop the movement of sediment after a rain fall. Even though some corals can remove the sediment by sloughing off mucus which removes it to clean themselves but, this does not always work when the sediment is too great (Castro pg. 292). About seventy-five to eighty percent of the sediment entering the world ocean's comes off the land in the tropical western Pacific and half of that is coming from Continental high lands (Birkeland pg 6). In recent years, humans have changed the basin's drainage through deforestation and farming. Since farming began there is four times as much sediment, nitrogen, phosphorus that has entered the marine environment (Birkeland pg. 6) The sedimentation affects the corals in a few ways that make them incapable to grow. Like the shading of the sea weed the excess sediment does the same thing. As the silt moves around and covers the corals completely the corals secrete a mucus that removes the sediment from them this is how they clean themselves. The light cannot penetrate through the solid masses of the soil in which the corals become smothered and the zooxanthellae with in the corals can not produce the proper nutrients because there is no light getting through. The corals also do not settle down on the soft sediment, they prefer areas that have hard rock or a steady place to plant themselves to begin to grow. Humans and animals also play a role in bleaching of the corals. Even though the turtles and fish do not stick around for a long period of time they still do a substantial amount of damage to the coral reefs. Animals such as the sea turtles go to the corals looking for organisms that are hiding within the corals such as the sponges and other organisms that hide near the floor of the ocean being protected by the corals. The turtles go down to the bottom and break pieces of the coral to reach the floor where the organisms are. This causes the corals to become stressed. The parrot fish is also another animal that would cause the corals to become bleached as the sea turtles have. The fish have a sharp hard beak which it uses to break off pieces of the coral to consume the nutrient rich algae that are covering the corals (NOVA (tvshow)). There are also many other animals that use the coral for food. Humans are just like the sea turtles, although humans do not destroy the corals to reach the hiding organisms below them. Human like to scuba-dive and when they do they go down to the bottom and touch the corals which affect them. In some parts of the ocean humans break and collect them to be sold or used in or as medicines. These behaviors in some way do stress the corals and sometimes to the point where they become bleached, the corals may only be bleached for a short time because this does not happen all to frequently or at a steady pace. And since it does not happen all the time the corals have time to obtain more zooxanthellae. There is also pollution and salinity changes in the water that stress out the corals. The corals stay in a region of normal marine salinity which is between 3.3 ppt and 3.6 ppt. When the corals go below these levels there is a build up of carbonates and organisms such as oysters, blue-green algae, serpulid and vermetids begin to dominate the area (Birkeland pg. 52). Since the corals cannot tolerate the changes in salinity, they remain away from areas that have fresh water flowing into the open ocean. Pollution is another aspect which corals are sensitive to and the larvae are the most sensitive. Pollution's such as chemical pesticides, are put onto the farm lands to kill off unwanted bugs that consume the crops. When it rains the chemical Pesticides, run off into the oceans where it affects the Coral reefs. Another type of pollution is garbage such as plastic bags, when the plastic bags enter the water stream it travels with the current and sometimes organisms try to eat them because they look like jelly-fish and sometimes it makes its way down onto the coral reefs. The plastic bag will lay on top of the coral where the zooxanthellae cannot work properly causing them to become stressed, which sometimes leads to bleaching (Sverdrup). Diseases are also a cause of some bleaching, diseases that are transmitted are unknown to scientists. There are many diseases that can affect the corals such as the black band disease and the white band disease, these diseases actually kill the coral tissues as it moves across the corals leaving behind the white skeleton behind (Coral Disease). The major component of black band disease is a photosynthesizing filamentous cyanobacterium. This disease has many different microorganisms which include cyanobacterium, heterotrophic bacteria, sulfur- oxidizing and sulfate-reducing bacteria and other microorganisms (Rutzler and Santavy). Black band disease affects corals that are already under stress and it most likely happens in warmer temperatures. When the black band disease passes over the corals, it is blackish in color and in a crescent moon-shape ranging from one to thirty millimeters wide and up to two meters long (Major Reef-building C...