Anthropogenic Disturbances of Coral Reefs
This topic submitted by Allie Cummins (
allie.cummins@gmail.com) at 8:05 PM on 6/6/08.
A green
snake close-up, Hospital Pt, Panama.
Coral reefs are, without a doubt, some of the most spectacular structures on Earth. A coral reef is a marine environment comprised of a variety of species, each of which depend on each other for survival within an intricate web of life. Coral reefs are to water what Rainforests are to land, important ecological environments that provide homes for a multiplicity of creatures. However, although coral reefs do not exist in our immediate surroundings, we humans have large impacts on their survival and abundance around the world. The balance of the coral reef ecosystem can naturally be distressed by such disturbances as hurricanes or predators. Yet, amazingly, such ecosystems have the natural ability to recover from this destruction. However when mixed with stresses that humans cause to the environment, this recovery process is easily upset. Reefs are structured through the aesthetically beautiful creatures we generically refer to as coral. In this paper I will focus specifically on the ways in which anthropogenic factors impact the survival of coral, vital animals within this underwater world, addressing such issues as increased sedimentation, pollution and eutrophication, coral bleaching, and tourism.
Coral are living animals. They are comprised of organisms called polyps, which are characteristically similar to such things as sea anemones or jellyfish. These coral polyps typically exist as identical individuals within colonies creating the different shapes that are unique to each type of coral. For example, Acropora palmata is shaped like an elkhorn, while Porites porites are constructed in finger-like shapes. To eat, polyps use their stinging cells called nematocysts, which are explosively discharged to both harpoon and poison their prey. Within the tissues of coral polyps thousands of single-celled algae called zooxanthellae live, forming a symbiotic relationship between the two organisms. This relationship is beneficial to both sides; the zooxanthellae obtain nutrients from the coral polyp waste, while the corals gain the ability to form calcium carbonate through zooxanthellae, a rock-like substance that forms the skeleton so characteristic of stony corals.
Coral reefs that currently exist in their massive sizes are incredibly fragile and important to protect, because the growing process of coral skeletons is a slow one. To provide an example, Acropora cervicornis is one of the fastest growing corals, growing only inches each year, yet still a rapid rate compared to others. On average most corals grow seven to ten millimeters a year. Thus, when destroyed, corals do not quickly recover. There are various circumstances needed for coral to thrive, such as water clarity, and steady temperatures. When anthropogenic actions put pressure on these circumstances the health of coral reefs begin to diminish, affecting their size and diversity, leading to devastating loss of marine life.
One environmental characteristic that coral needs in order to thrive is sunlight. As mentioned earlier, zooxanthellae play an important role within the life of coral. Zooxanthellae are algae that feed through photosynthesis. Thus, coral thrive in shallow water where sunlight is abundant. If not provided the sunlight needed for growth, coral canÕt gain the nutrients needed to survive. Lack of sunlight can often times be a natural issue, for example coral will not thrive in deep waters or when covered by other larger, overgrown coral structures. However, human factors can affect sunlight as well, an example of this is a decrease in water clarity through an increase of sedimentation, a process that comes about through actions on or close to the shore, sometimes miles away from the actual reef.
Coral are tolerant to small amounts of sediments, but too much becomes harmful, fogging the waters and preventing sunlight from reaching the zooxanthellae. Too much silt also damages and sometimes kills corals that are not able to handle large amounts. The majority of heavy sediment comes from the land, washed from shore through heavy rains that disrupt unsteady soils. The erosion of soil is caused most commonly through development projects, such as building a road, or through mining, as well as through poor agricultural methods. These activities leave the soil lose and more likely to be washed away to shore through streams and rivers and eventually onto reefs.
In Geological Approaches to Coral Reef Ecology Rechard B. Aronson asserts, ÒThe most publicized issue related to the demise of coral reefs is declining water quality [É] the increased abundance of algae observed on reefs over the last two decades supports an intuitive assumption that nutrient enrichment must be the causeÓ (269). Another example of human caused stress is Eutrophication, the process by which excessive richness of nutrients in a body of water often build up due to runoff from the land. This causes a dense growth of plant life, and a death of animal life due to lack of oxygen. Thus, when water becomes overfilled with nutrients, algae tend to thrive while coral, and other animal life on the reef, die. Eutrophication is caused by pollution through such things as agricultural runoff and sewage waste. In fact, in the Florida Keys, sewage pollution is considered to be the cause of coral reef ecosystem decline. A gross fact is that billions of litres of sewage are pumped into the sea daily worldwide (Wells, 79).
When the natural environment of the water is changed and stressed from outside sources, so too is the growth of coral. One large issue related to a change in environmental conditions is that of coral bleaching, which results from a loss of zooxanthellae. The loss of zooxanthellae is related to such stressful circumstances as poor water circulation, an influx of fresh water, and elevated temperatures all of which factor into the ejection of zooxanthellae from the coral tissue, in turn creating a lack of photosynthesis. This lack of photosynthesis means that coral lose not only their color but also vital nutrients, often times leading to death. While coral can slowly recover from bleaching, they often times do not.
It is suggested that coral bleaching is largely a result of global warming. In An Inconvenient Truth Al Gore asserts, Òthe link between global warming and the large-scale beaching of corals, considered controversial only 10 to 15 years ago, in now universally accepted [É] in 1998 the second hottest year on record, the world lost an estimated 16 % of all coral reefsÓ (164). Global warming is a process that humans contribute heavily to through our use of fossil fuels through activities that we partake in daily, such as driving a car or running our air conditioning, even in cutting down large forests. These activities increase greenhouse gases and in turn put stress on marine environments through the changes mentioned above. Whether or not coral bleaching is a result of global warming or anthropogenic pressures, it certainly is a signal for a need to increase both protection of reefs, as well as encourage sustainable usage of coral. For, the likelihood that coral will survive something like coral bleaching and increased temperatures is much greater for healthy reefs as compared to damaged ones.
Tourism is yet another issue in the destruction of coral reefs caused by humans. In coastal areas such as Florida reef tourism is vital to the economy. Greenpeace asserts that Florida gains up to $1.6 billion each year through the industry. However, not only does reef tourism attract people and money, it attracts pollution, habitat destruction, and damage as well. This is a problem all around the world, including places such as Australia, the Caribbean, and Hawaii. Along with tourism come beach resorts, hotels, golf courses, and airports to name only a few developments. This disrupts coastal ecosystems, not only creating more erosion through building but also destroying important ecological organisms, mangroves often being the first victims; ripped out in order to be replaced by tourist attractions. This is a disaster for the reason that each part of the marine world is connected, depending on one another for survival and if one aspect is lost, such as Mangroves that provide protection as well as nurseries for marine mammals, everything becomes off balance.
Along with building on the coast, tourism causes trouble within the water, particularly through anchoring and disturbances caused by divers. Anchoring by cruise ships causes severe damage through the mixture of heavy anchor chains and the anchor itself that crush coral and stir up huge amounts of sediments. Rather recently, though, this problem has been subsided through mooring buoys, which are installed by divers on reefs and have effectively prevented damage on heavily visited reefs. Divers cause trouble through ignorance, standing on coral, posing with it for a picture, or accidentally bumping into it, not aware that their seemingly innocent interactions are killing the coral polyps. One possible prevention to this problem offered by Greenpeace is to create smaller-scale developments with less visitors and in turn less destruction.
In Marine Life of the Caribbean, Alick Jones asserts, Òas compared with the 1970s, coral reefs have been afflicted by a series of setbacks which have left them much diminishedÓ (141). The destruction of coral reefs through anthropogenic disturbance is a reality and, if anything, I think that our effect on the ecosystem as a whole illustrates the importance not only to put a lot of energy into protecting marine environments but it also illustrates just how connected and fragile this ecosystem is, each part depending on another, sometimes in ways we wouldnÕt even imagine. Works Cited
Aronson, Richard B. Geological Approaches to Coral Reef Ecology. Springer: Dauphin Island, Alabama, 2002.
Davidson, Osha Gray. The Enchanted Braid. John Wiley & Sons, Inc.: New York, 1998.
Gore, Al. An Inconvenient Truth. Rodale: New York, 2006.
Jones, Alick. Marine Life of the Caribbean. Macmillan Education: Oxford, 2002.
Murphy, Richard C. Coral Reefs: Cities Under the Sea. The Darwin Press Inc.: Princeton, New Jersey, 2002.
Wells, Sue. The Greenpeace Book of Coral Reefs. Sterling Publishing Co., Inc.: New York, 1992.
Wood, Rachel. Reef Evolution. Oxford University Press: Oxford, 1999.
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