Coral Bleaching Essay, Research Paper
Coral reefs are the most biodiverse ecosystem on the planet. There are more than 25,000 known species of organisms and countless others that have yet to be identified (Helvarg, 2000). Reefs thrive on the shallow edge of tropical seas, most often on the eastern edge of continents along warm water currents that brush the coasts. Reefs cannot live in cold waters and are limited by ocean depth and available sunlight. Coral is the foundation of the reef community, providing a three-dimensional structure where thousands of species of vertebrates and invertebrates live and feed. Some species of coral are hard, while others soft. Some are branched, yet others are compact and rounded. Coral is made up of large communities of tiny jellyfish like polyps. These polyps absorb calcium from the sea water and secrete a hard limestone skeleton. At night the polyps extend sticky, stinging tentacles from their skeletons to capture and consume small floating organisms such as zooplankton. Every coral has a two-stage life cycle: the larva, and the polyp. The larval stage is free swimming, and the polyp is stationary. Ocean currents carry the larva from the stationary parent polyp to any hard, clean, silt-free surface where, if the conditions are perfect, the larva grows into a coral forming polyp, never to move again (Levin, 1999). One of the most valuable resources for coral polyps are algae. Some live on the coral skeletons, but one type in particular, zooxanthellae, lives inside the tissue of the polyps. Zooxanthellae makes up about half the weight of the fleshy polyps and are not only a valuable food resource, but they are responsible for the brilliant colors associated with coral. When coral looses these precious colors it turns white, a phenomenon known as coral bleaching. The purpose of this paper is to compare the notion of coral bleaching in scientific literature and studies to those in the popular press.
Coral bleaching is normally characterized by the expulsion of the zooxanthellae algae, loss of algal pigmentation, or both. Coral bleaching events have had serious effects on corals and reefs worldwide. What is crucial to the understanding of zooxanthellae expulsion and bleaching is how the density of zooxanthellae within the coral is changing, if at all, under the prevailing range of environmental conditions (Gates and Edmunds, 1999). Over the last twenty years, there has been a dramatic increase in both the frequency and intensity of coral bleaching events. Sixty major bleaching events have been reported between 1960 and 1979, whereas only nine were reported prior to 1979 (Huppert and Stone, 1998). Given the dependence of the coral on this symbiotic algae, it is important to determine the cause of these bleaching events. According to Helvarg (2000, p.12):
“Coral reefs? are fragile structures living within a narrow range of temperature, clarity, salinity and chemistry. Even a slight increase in ocean temperature, or increased CO2? can cause stresses such as bleaching? These stresses slow the rate of growth of the corrals? With some 60 percent of the world?s coral reefs now losing productivity, it?s becoming a global crisis and a scientific mystery.”
Scientists have been trying to solve this “scientific mystery” by evaluating each environmental condition that may be a cause for coral reef bleaching. A number of explanations for coral bleaching have been proposed, including unusually high
seawater temperatures, high doses of ultraviolet light, bacterial infection, and changes in salinity. Huppert and Stone (1998) published a report on coral reef bleaching. They tested the role of the ocean?s natural El Ni?o cycle and how “hot spots,” concentrated areas of the ocean that are abnormally warmer than average conditions, may affect coral bleaching. They attempted to demonstrate how environmental conditions, in particular temperature, determine the regularity in which hot spots occur and, hence, the consistency of the bleaching events themselves. Huppert et al. (1998, p. 1) suggests that:
“Perhaps the most striking finding is the possible existence of a ?worldwide coral reef bleaching cycle,? peaking every 3-4 yr? [and] that this cycle is intimately tied with strong El Ni?o events, which heat large areas of the? ocean.”
While Huppert and Stone maintain that the warming of ocean waters could just be the result of nature?s El Ni?o cycle, Winiarski (1998, p.4A) reported that global warming is to blame. In global warming, the burning of fossil fuels discharges extreme levels of carbon dioxide, trapping heat around the planet like a thick blanket. Winiarski (1998) reports that reefs will survive only through a dramatic decline in the consumption of fossil fuels. Warrick (1999, p.6) seems to stress that the recent influx in bleaching and subsequent mortality is a combination of El Ni?o and global warming. Warrick (1999) reported that in 1998 coral reefs around the world appear to have sustained the most expansive and brutal bleaching events in the modern record. He adds that the conditions in 1998 were aggravated by El Ni?o and that recent trends suggest that the threat to coral reefs will only increase with time. The article continued in stating that it is plausible that global warming could have affected such vast bleaching concurrently throughout the widespread reef regions of the world. “Thus the geographic extent, increasing frequency and regional severity of mass bleaching events are likely a consequence of a steady rising baseline of marine temperatures” (p.7).
It is evident that there is not yet enough information on the topic of coral reef bleaching to arrive at any concrete conclusions about why it happens. Since it is a relatively new phenomenon it is entirely fair to call it a scientific mystery. It is known that temperature increase over a sustained period of time does play an active roll, but there is some discrepancy in the cause of the elevated temperatures. Furthermore, there are plenty of other environmental conditions such as high doses of ultraviolet light and bacterial infection that may be limiting the ability of the symbiotic algae zooxanthellae. Nevertheless, there is but little scientific data to ascertain any definitive cause. Both scientific literature and the popular press report that there is a problem and that temperature increase is one of the conditions that causes coral bleaching. According to Huppert et al. (1998) the cause is El Ni?o, but Helvarg (2000) suggests that CO2 may be a legitimate reason, which it may be. The opposing viewpoints between Huppert et al., reputable scientific authority, and Helvarg, a member of the popular press, are not so much in opposition due to their cultural status, but rather they are both reporting on an issue that has yet to have a determinant cause. The same holds true for the views of Winiarski (1998) and Warrick (1999). On the topic of coral reef bleaching, and since it is a new notion, the popular press is probably more capable of expressing this knowledge to the general public. Huppert et. al (1998) and Gates et al. (1999) merely touch on the principles of coral bleaching before exploring the in depth tests and models that were conducted in search of a very specific fragment of the general subject. While on the contrary, authors such as Helvarg (2000), Winiarski (19998) and Warrick (1999) have the benefit of being able to describe what coral bleaching is and it?s probable causes in a much more concise and to-the-point fashion.
Gates, R.D., and Edmunds, P.J. 1999. The Physiological Mechanisms of Acclimatization in Tropical Reef Corals. American Zoologist; Vol. 39, No. 1 (Feb. 1999), pp. 30-43.
Huppert, A., and Stone, L. 1998. Chaos in the Pacific?s Coral Reef Bleaching Cycle. The American Naturalist; Vol. 152, No. 3 (Sept. 1998), pp. 447-459.
Levin, T. 1999. To Save a Reef. National Wildlife; Vol. 37, No. 2 (Feb./Mar. 1999), pp. 20-29.
Warrick, J. 1999. Warm Weather Destroyed Corals in ?98, Report Says. Houston Chronicle; March 8, 1999, p. 6.
Winiarski, K. 1998. Coral in Peril as Reefs Suffer Worldwide. USA Today; October 19, 1998, p. 04A.
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