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Global warming has been a hot topic for several years now and something I am very concerned about. I lived on St. Thomas in the US Virgin Islands for a year and came to love the coral reefs near itsÕ coast. After speaking at length with several people who have lived on the island for twenty or more years, I was made aware of the fact that the reefs have changed dramatically. For this reason I have decided to investigate why this is happening, how wide spread the problem is around the world, and what can be done about it.
As a teacher and an MAT (Biology) student, I feel the best place to begin is to look closely at the basic anatomy of the coral animal. Reef building corals are colonial animals made up of individual polyps joined together. Each polyp consists of a limestone skeleton, small tentacles that surround a gullet, and single-celled algae called zooxanthellae that live in their tissues. The zooxanthellae and the coral have a symbiotic relationship where the coral provides protection and nutrients they release as waste while the algae provides food to the coral as they photosynthesis.
Just like any animal, corals have specific needs for survival. One of the most important requirements for a coral reef to grow is a water temperature no lower than 64ÕF. A second requirement is for shallow, clear water with a certain amount of hard seafloor to grow on. Many times coral reefs develop near mangroves and sea grass beds as mentioned in The Enchanted Braid, mutually supporting and protecting each other.
There are two major categories of corals- hard corals and soft corals. Hard corals build limestone skeletons and are what build the reefs around the world. There are about a thousand species of hard corals. Soft corals do not build reefs or have a hard outer skeleton. A majority of corals are very slow growing. Currently coral reefs cover 7% of the EarthÕs surface, but only 1% of that is fast growing corals.
Coral reefs are extremely important to the planet. They provide a nursery for other organisms to feed and grow on. In fact, they are second only to tropical rainforests in the biological diversity found within them. Coral reefs recycle nutrients and help mutually support sea grass beds and mangroves. Over a hundred million people around the world live near the coast and depend upon the food they catch in the ocean.
Those same coral reefs also protect the shore from flooding and erosion, while at the same time generating billions of dollars a year in tourism. The Great Barrier Reef in Australia alone brings in $6.8 billion dollars a year in international tourism. Some cancer drugs are even derived from organisms found within coral reefs.
After understanding the anatomy of the coral polyp, what they need to survive, and why we need coral reefs, my next task was to examine how big a problem global warming is to coral reefs. I was very surprised to find out that as of 1998 11% of the worldÕs reefs have been destroyed by human activity and 16% were damaged by coral bleaching. Coral bleaching occurs when the zooxanthellae are expelled from the coral polyp because it can no longer photosynthesis. This leads to the coral starving to death. An example of this was observed in AfricaÕs Seychelles islands in 1998. In the same year, El Nino sparked the worst coral bleaching event ever observed.
In September 2005, the water temperature in the Caribbean started to rise, which resulted in almost 90% of the coral around the US Virgin Islands bleaching. Some of these corals never recovered. This was followed by an outbreak of disease that caused an additional percentage of coral to die.
Researchers at the University of North Carolina completed a study in August of 2007 that showed between 1968 and 2003, more than 600 square miles of reef in the Indo-Pacific region disappeared. Even reefs that were considered isolated and therefore somewhat protected suffered damage.
Needless to say, this was very depressing to me. I wanted to find out what was causing all of this death and destruction. Once again, I was surprising to find how complicated the problem is. There are many reasons why coral reefs are dying in record numbers and therefore the solution will be much harder to attain.
I have already mentioned coral bleaching. This can be caused by the reef being smothered by dust or sediment, an increase in water temperature, or an increase in water depth due to glaciers melt, etc. I have also already mentioned coral diseases. These diseases can dramatically affect corals that have already been weakened by coral bleaching. Non-coral diseases can also affect coral reefs. In the US Virgin Islands, a disease killed most of the spiny sea urchins, which are herbivores that feed on plants that compete with the corals for room to grow. Anything that removes plant-eating organisms from the equation will upset the balance and affect the reefs.
Another problem is run-off pollution. It is generally believed that outbreaks of the crown of thorns starfish in Australia, which feed on coral, can be linked to humans leaking nutrients into the water. Artificial fertilizers have affected the global phosphorous and nitrogen cycles around the globe. These starfish thrive on it and reproduce quickly.
Others causes include overharvesting, introduced or invasive species, sedimentation, increased storm frequency and intensity, commercial destruction, decreased ocean salinity, and a carbonate ion decrease. This may be one of the most serious problems. An increase in atmospheric carbon dioxide affects the ocean chemistry inhibiting the ability of corals to calicify or build their limestone skeletons. One study shows that levels of CO2 could become unsustainable for coral reefs in as little as five decades. The oceans will become to acidic to sustain them.
The concentration of carbon dioxide is now at 380 parts per million and that is 80 parts per million higher than where it has been for the last 740,000 years. This has caused the temperature of the Earth to already rise 0.74ÕC. A rise in the temperature of the water at the surface of the ocean by only 1% can cause massive coral bleaching. The CO2 levels are expected to exceed 500 parts per million by the end of the century and increase the temperature by 2ÕC.
Coral reefs are the proverbial canary in the gold mine. They are very sensitive and are affected first. So what can we do about this? After researching the answer to this question, I came away feeling both hopeful and sad. Most researchers believe that even if we stopped releasing any CO2 into the atmosphere tomorrow, the damage has been done and it will take hundreds or thousands of years to revert to the natural balance. What we can do, however, is decrease the local stresses many coral reefs are under. This will take global cooperation.
There are several organizations working towards this end now. One of those was formed in 1997 called Reef Check. It is a network of volunteers around the world that are trained by scientists to monitor reefs using a checklist. Another group working towards global cooperation is NOAA or the National Oceanic Atmospheric Administration (US Department of Commerce). They have put together a system of satellites that monitor water temperature and look for potential problems. This information is shared through an alert to communities and reef managers. They have also been partnering with the World Bank and 70 other countries to reduce over fishing and pollution and other causes of reef destruction by helping to develop local action plans and provides funds for implementation.
Other important solutions to the problem include the formation of marine sanctuaries and coastal management zones. One national park scientists said that marine parks can serve as replinishment reserves for other coral reefs not protected by law.
Lastly, a technique called Biorock Reef Restoration is in the testing phase. This technology uses safe low voltage electrical current, usually provided by solar panels, to grow solid limestone structures. The structure grows an inch a year and becomes stronger as time goes on. Coral fragments transplanted to them grow 3 to 5 times faster and can withstand higher temperatures up to fifty times more than surrounding reefs.
People are beginning to take notice of the problem and to find solutions to minimize the affects of excessive CO2 in the atmosphere. I have come away with an understanding that corals will probably not become extinct (they have survived for millions of years), but they will most likely become much more rare. I have also come away knowing that a lot of the problems are caused by poverty. Until this can be tackled, we may not be able to stop what has begun.
One of the most poignant statements in the book The Enchanted Braid was, ÒYou have to turn off the faucet before you start mopping the floor.Ó Somehow we need to find a way to stop the chronic stresses and the acute stresses. Thomas Goreau said, ÒWe have to do it all; all at the same time.Ó That is a tall order. If we work together, I believe we can do it.
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