The earth's axis of rotation wobbles like a spinning top. There are two periods (a wobble within a wobble): 19,000 AND 23,000 years. Precession has a profound effect on the earth's climate.
An Intricate and Nessecary Part of Our World
There is no doubt that coral reefs are spectacular parts of our planet’s vast oceans. They are filled with vibrant colors and a wide variety of marine life forms. “In comparison with the reef, the rest of the ocean is a desert. Although coral reefs represent less than two-tenths of 1 percent of the area of the global ocean, approximately one-third of all marine fish species are found in this tiny zone” (5 Davidson). But if current trends continue, we will not be able to enjoy these sights much longer. "For example, the results of the first global survey of human impact on coral reefs involved 250 corals and 30 countries around the world. The surveys revealed no pristine reefs; in almost every case there were visible signs of human impacts (Hatziolos 4)." Some of these reefs were totally void of high valued species of coral. Were fishing for sharks, lobster, giant clam, and grouper was present there was evidence of "cyanide and blast fishing (Hatziolos 4)." Much of the reefs species are valuable and many of them are harvested relentlessly. These are not the only problems that modern coral reefs are experiencing. Much of the reef populations are enduring hardships as a result of. If these problems and more continue at there current rates, our grandchildren may not have these wonderful reefs to experience.
Reef building corals such as stony (hermatypic) corals are able to build reefs tens to thousands of meters across. But as these corals become adults they become stationary. These vast reefs provide habitats for many of the ocean’s species. These reef building corals need a very specific environment to thrive. The water must be warm, clear, saline, and are mostly nutrient poor as well. Because most coral is confined to one spot on the sea floor, they have developed methods of reproducing that allow them to thrive. Corals have evolved to reproduce both asexually and sexually. In asexually reproduction, new polyps bud off the parent coral and expand to form new colonies. This happens when a parent coral reaches a specific size and then divides. A coral is able to do this many times throughout its life time. Sexual reproduction among stony corals varies. Most species have the ability to produce both male and female gametes while the rest are only able to produce either male or female. Sexual reproduction takes place because the corals release a massive number of sperm and eggs into the water which then fuse in the water creating a planktonic larva. These larva are called planulae. A moderately sized colony will produce thousands of these palnulae to compensate for the many hazards that they undergo. In contrast some corals species keep the palnulae within their bodies. They produce much fewer but the mortality rate is also much lower. Internal fertilization also results in larger better developed palnulae.
The mass spawning that is required for the reproduction of the external fertilization corals has to be precisely synchronized. They are able to release their gametes simultaneously because of various environmental cues. The long term maturing of their gametes is controlled by the temperature, length of day, and rate of temperature change. The short term cues used for when the corals are getting ready to spawn are lunar, while the actual time of release is controlled by the time of sunset. Internal fertilization species are able to hold their eggs for weeks so it is not so important to be synchronized in their release.
There is a very close relationship between stony corals and zooxanthellae. Zooxanthellae are single celled, photosynthetic organisms which live in the endodermal tissue of stony coral polyps. Almost all reef building corals possess them. During photosynthesis, zooxanthellae produce large amounts of carbon which is passed on to the host polyp. This carbon is in the form of glycerol, glucose, and alanine. These chemicals are essential in the production of proteins, fats, and carbohydrates in the coral itself. Because of this close relationship with photosynthetic organisms, most corals’ environments are very similar to those of plants. Another method of obtaining nutrients is to actually capture prey. Most corals that have zooxanthellae also must filter feed on zooplankton as well. These corals feed at night when their polyps extend tentacles that sting their prey and then draw them into their mouth. Corals are not only amazing in their mating and feeding habits but they are also beautiful. Aside from their beauty, they also have a very strong environmental and economical impact on the rest of the world.
People have some very harsh habits associated with coral reef destruction. One of these is waste disposal. The introduction of sewage into waters containing coral reefs can have several damaging effects. First the sewage and other wastes cloud the water. Reef building corals depend on zooxanthellae and their photosynthesis as a means of food production. As a result of the clouding water, less sunlight can penetrate the photic zone. So the zooxanthellae are unable to photosynthesize which results in something called bleaching. Bleaching is what it sounds like, the coral looses its color. Because the zooxanthellae are unable to photosynthesize they die, leaving the coral colorless. This is very detrimental to the corals since they receive much of their nutrients form these zooxanthellae. Most corals are unable to grow or reproduce and many die. Another reason that the introduction of human waste results in a loss of reef stability is that the waste its self is filled with nutrients. Coral reefs generally develop in nutrient depleted waters. So when a large amount of nutrients are introduced into a very delicate environment, the algae is able to overgrow the reef which in turn results in the eventual destruction of that reef. Davidson gives us a personal account of this wide spread destruction in the Indonesian city of
Over fishing can have dire impacts on the reef environment as well. “Many reef species, including giant clams, sea cucumbers, sharks, lobsters, large groupers, snappers, and wrasses, are now fetching high prices both on domestic markets and internationally” (13 Bryant). Because the demand is so high, the tendency to over fish an area is very common. Fisherman reach an area, catch their desired species and leave. But they may leave that particular area completely void of an entire species. Not only does over fishing put hardships on the species of fish being exploited, but it also puts hardships on the intricate ecosystem. Without many of these species of fish that feed on algae, the algae is free to spread unchecked. Once again the algae are able to over grow and in a way suffocate the reefs themselves. Another damaging habit that is less of a threat than over fishing is the use of destructive fishing practices. The only reason that these forms of fishing are less destructive is because they are much less wide spread. There are several methods considered to be destructive fishing practices. Some of these practices are “blast fishing, fishing with cyanide and other poisonous chemicals; muro-ami netting (pounding reefs with weighted bags to scare fish out of crevices); and in deeper waters, trawling directly damage corals” (12 Bryant). Cyanide is used in fishing as a means of stunning the fish so that it can be captured alive for use in aquariums or in restaurants that allow customers to pick a live fish to have prepared. This type of fishing is widely illegal but it goes on due to poor enforcement along with corruption. Studies have shown that “cyanide kills corals, and its toxic effects on fish are well known” (15 Bryant). The cyanide its self is squirted at fish at which point the fish usually flee into crevasses in the reef. Then the fishermen break and pry apart the reef to get the stunned fish. It does not take much to imagine how detrimental this is for the coral.
Around the world “millions of people depend on reefs for a source of food and livelihood” (4 Gustivason). In
1. Reefs At Risk: A Map-based Indicator of Threats to the World's Coral Reefs, By: Dirk Bryant, Lauretta Burke, John McManus, and Mark Spalding, World Resources Institute, 1998.
2. Integrated Coastal Zone Management of Coral Reefs: Decision Support Modeling, By: Kent Gustavson, Richard M. Huber, and Hack Ruitenbeek, The International Bank for Reconstruction and Development,
3. Coral Reefs: Challenges and Opportunities for Sustainable Management, By: Marea E. Hatziolos, Anthony J. Hooten, and Martin Fodor, The International Bank for Reconstruction and Development, Washington, D.C. 1998.
4. Reefs and Related Carbonates: Ecology and Sedimentology, By: Stanley H. Frost, Malcolm P. Weiss, and John B. Saunders, The American Associatin of Petroleum Geologists, Tulsa, Oklahoma, 1977.
5. Auquatic Invertabrate Cell Culture, By:
6. The Enchanted Braid: Coming to Terms with Nature on the Coral Reef, By: Osha Gray Davidson, John Wiley and Sons Inc.,
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