Coral reefs are defined as shallow structures which are made by corals and other hermarphic organisms and they are sometimes associated living components such as the corals. The reefs are the most important areas in terms of productivity, reef growth, diversity and coastal protection. Coral reefs grows upward from the sea floor as the polyps of new corals cement themselves to the skeletons of those below and provides support for algae and other living organisms whose secretions serve to bind the skeletons together. The resulting structure provides a habitat for a wide variety of fish and the marine invertebrates and also plays an important role in the world's economies, heritage and culture. The coral reef health in the word has been on a serious decline for decades due to the warming seas and ocean acidification which slows the formation of coral skeletons and increased bleaching events. This essay presents the future scenarios for coral reefs that predict some dangerous consequences for reef-associated fisheries, coastal protection, tourism and people.

The unusual changes that have already happened

When the fossil fuels are burnt, carbon dioxide is released into the atmosphere. Many scientists say that the increase in carbon dioxide has already contributed to air and ocean warming. The ocean absorbs a third of the carbon dioxide which is added to the atmosphere each year. This carbon dioxide reacts with the water to make carbonic acid. The global ocean's pH level has already dropped from around 8.1 to 8.0; and this is referred to as ocean acidification. This change to the ocean's chemical configurations makes it much difficult for the corals to build their calcium carbonate skeletons. Scientists use the gases from bubbles trapped in the ancient Antarctic ice to estimate the composition of the atmosphere. Based on the analysis, they believe that the fossil fuel burning raises the carbon dioxide in the oceans and lowers Ph to a level which is much less than at any time in the past years. And, all three of these indicators are changing much faster than in the past. Estimates show that atmospheric carbon dioxide and temperature are changing at least 100 times faster now than in the last 420,000 years making the natural systems not to adapt quickly to keep up with this rate of change (Braasch G. 2009).

Coral Bleaching and Ocean Temperature

Corals possess a mutually beneficial relationship with the algae living in their tissues. The algae receive nutrients and a safe place to photosynthesize and grow. And, in return, it becomes the main corals' food source. The high temperatures cause the normal photosynthetic process to break down, making algae harmful to their coral hosts. The corals then kick out their algae partners. Because the corals' color comes from algae, the expulsion causes corals to turn a pale white color referred to as coral bleaching. High ocean temperatures kill the corals if the warm conditions last for a very long time. Even if the corals survive a bleaching event, the stress increases their chance of overcoming diseases and reduces their reproduction capability to for the years afterwards (Braasch G. 2009).

Reef Growth and Ocean Acidification

Recent experiments clearly show a relationship between ocean acidification and corals' ability to develop their skeletons. As the amount of carbon dioxide in the atmosphere increases, so too does the amount of carbon dioxide in the ocean, causing the corals and other organisms to grow at a very slow rate. This is because higher carbon dioxide levels in the ocean not only reduce the pH, but also reduce carbonate ions which are vital for corals to develop their calcium carbonate skeletons. Some evidence from Australia's Great Barrier Reef indicates that the coral growth rates have dropped by about 15% in the last 15 years.  Corals may also build less solid skeletons, making them more vulnerable to erosion, grazing animals and storm damage.

The non-climate threats

It cannot be emphasized enough that climate change is not the only factor affecting the future of coral reefs. Local stresses threatening reef health include poor water quality, deforestation, overfishing, and sedimentation and nutrient runoff. Many reefs have lost several of their grazing animals due to fishing pressure or diseases. These animals are especially important in allowing reefs to bounce back because they control the algae growth. If algae are allowed to cover a reef after a storm or a bleaching event, it is very difficult for the new corals to grow back in that area.

What will the future bring?

What the future brings is very much up to everybody, and the actions we take in the next ten years are significant because it takes a while for natural systems to react. As mentioned, most scientists expect a higher ocean temperature by the end of the century just from the carbon dioxide already in the atmosphere. That is to say, even if we stop adding carbon dioxide to the atmosphere today, further warming and acidification will occur before the earth's system comes back to the required balance. There are different scenarios that demonstrate the potential effects of climate change and how the peoples' actions determine the coral reefs' future. The scenarios show three possible futures i.e. where we take very strong action to control the carbon dioxide emissions, where slower action allows higher concentrations of carbon dioxide and where the carbon dioxide levels rises unchecked.

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The human activities determine which scenario becomes a reality. Also, the way people manages the serious local threats is important. Some of the reefs will devolve to scenario two or scenario three because of the severe local problems, while a healthy and a well protected reef is better and able to survive the climate changes (Braasch G. 2009).

This is an optimistic scenario, where people take strong action soon, and atmospheric carbon dioxide levels off very fast. Reefs continue to change, but may stabilize in a relatively healthy condition. Local effects from erosion, fishing and other ways people harm the reefs determine the health of each coral reef. In those areas where the local stressors are minimized, the corals continue to dominate, but grow more slowly than they did in the past. The coral reefs may be less healthy than they are today, but are able to grow faster than they are eroded and coral species most sensitive to bleaching may die out, leaving reefs dominated by the tolerant massive coral species such as Porites that are able to grow more quickly e.g., Acropora table corals.

If the people do not slow emission rates fast enough, the carbon dioxide levels rises to about 450 ppm which is double the amount of carbon dioxide in the atmosphere before people started burning fossil fuels. At these levels, the ocean pH drops to a level where the reef growth cannot keep up with erosion in most parts of the world. The temperatures rise at least 2° C/3.6º F, making the coral bleaching much more severe. The coral reefs become rare, the coral cover and diversity declines and there are fewer habitats for the 25 percent of all marine species that uses the reefs as their homes.

This happens to be the worst-case scenario where people continue their business as usual and the carbon dioxide levels rise well above 450 ppm. Under these conditions, the corals cannot grow fast enough to maintain the reefs. Also, the high ocean temperatures cause the frequent bleaching events. These changes reduce the coral reef ecosystems to crumbling frameworks with very few live corals. The potential for severe damage is highest where the local stressors have already weakened or damaged the coral cover. Those corals that manage to survive grow very slowly and are highly vulnerable to the local threats. Because of this, more than half of the species dependent on coral reefs becomes extinct (Herr D and Gallad R. 2010).

The importance of saving the reefs

The reefs are very important as many people in the world depend on healthy coral reefs for food, protection against storms and waves and to attract significant tourism income. The above three scenarios have very severe consequences for those economies and societies that depend entirely on coral reefs, e.g., less fish and other food species as their reef habitat is lost, effects of climate changes make the reefs less attractive to the tourists. The ocean divers in particular have a keen interest in healthy reefs and in preventing scenario three. The degraded reefs always offer less protection from the ocean waves and storms. This issue becomes more important as climate change causes sea levels to rise and storms to increase in strength, which also causes beaches to erode at a very high rate. This is a problem for the coastal populations, the tourism industry and for the animals that depend on beach habitats for their survival (Seckbach J. 2010).

What we do can make a difference

There is much that can be done by society to enhance the survival of the coral reefs. First, people can address the rise in the greenhouse gases. The people's daily actions affect the total amount of carbon going into the atmosphere, so taking steps to reduce their carbon footprint, e.g., switching to compact fluorescent light bulbs and using the energy efficient appliances and vehicles does matter. Since it takes long time for the climate to stabilize when the emissions are reduced, there are some significant actions that can be taken to protect the reefs from the harsh climate changes. They include; (Madeleine J, Oppen V and Lough M.2009).

Carrying out Coral Restoration Projects

The coral reef restoration is not yet practical on the huge scale demanded by the climate change. However, the new technologies for farming corals may make this a better option in future. Growing those corals best able to tolerate high temperatures improves the corals' chances of surviving.

Managing the Major Local Stressors

All the actions that people can take to reduce the effects of overfishing, improve water quality by pollution reduction, deforestation and sediment and nutrient runoff from land is very significant. For instance, more corals will survive and re-grow faster than a reef that is subjected to continuous and severe stresses. People are supposed to act very fast because if they wait for long time, they cannot achieve the required positive change.

Managing the Coral Grazers

This is the increasing of the number of herbivores on coral reef systems which eats the algae. Improving the sea urchin populations and limiting the fishing of important grazers like parrotfish is a significant step that gives the corals a fighting chance at surviving the bleaching effects.

If the strategies above are soundly implemented, they would preserve a substantial portion of the global biodiversity. The implementation requires the tremendous efforts, vision and knowledge on the biodiversity.

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