Maria

 NEXER Pierre-Alexandre Pierre-Alexandre 11019522

Assignement n°2

Coral reefs Intro Introduc ducti tion on : Coral reefs represent one of the most amazing diversity of species on Earth. The coral itself show an impressive variety, but more than that, it's an important habitat for many diverse species, forming an incredible ecosystem, full of life, in different zone of the Globe. But because this amount of species is so diverse, and induce complex exchanges, coral reefs are all the more likely to suffer from change in their physical parameters. Thus, we know that today, the major disruptive actor that t hat affect coral reefs is Global Warming and therefore we must protect them, knowing that they represent more than 25% of the marine  biodiversity. This is why we are going to sea how coral reefs are formed, and where, how Global Warming affect them and how the human can preserve these t hese “rainforests of the sea” from the extinction.

How are coral reefs formed ? Simply we can say that at the origin of the reef there was a empty space on a coastline, underwater. Then a coral larvae, free-swimming, as plankton, get fixed on a point on that empty space. When the first coral die, an other larvae grow, attached to the dead one. And then this cycle continues again and again to begin to form a true colony of corals, living in symbiosis. After a long period, the skeleton from dead coral begin to form a stony structure : it's the reef. Every time a single coral die, his skeleton is perfectly added, after a couple of years, to the reef structure. It's important to notice that the coral doesn't live inside the reef but only on the outermost layer, always under the influence of the sun and sometimes of the tide. After a long time, from hundred thousand to million years, the reef   begin to represent an important bulk, formed by accretion of millions dead skeleton into limestone, sometimes filled with sand. In fact, when the reef begin to formed, as the corals grows, depending on its position on the rock and the shoreline, reef take one of the three major structures, “main types” of  coral reefs, ie Fringing reef , Barrier reef and Atoll. These three main types have been widely adopted, based from Charles Darwin observations and reflexions in the 19 th Century. – The Fringing reef is by far, the most common. It simply consist for the reef to grow directly on and close the shoreline, with a single back-reef zone : the lagoon. As in the Red Sea, fringing reefs can follow the coast for hundred of  miles. – Barrier reefs are quite similar with fringing reef : parallel to the shoreline with a

lagoon. But instead of being close to the shoreline, barrier reefs can be spaced from hundred of meters to it, providing an important an deep lagoon. It is admitted that barrier reef are derived from fringing reef but have extended much longer 

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Finally Atolls are circular reefs formed around a sunk volcanic island. In fact Atolls were before Barrier reefs and again before Fringing reefs. An increase of  the sea level or a subsidence of the island formed a circle of corals around the lagoon. Atolls needs much more time to get totally formed, sometimes up to 30 millions years.

During the formation, the reef get settled by other organisms, small species first : algae, mollusc... which themselves attracts other species, more important in size : fishes. Then, after a while, other species can appear in proximity of the reef, depending on where it is, like shark, turtle... All this species begin then to exchange, living in symbiosis, forming a  particular ecosystem on diverse zone of the globe.

Where are coral reefs found ? Contrary to common beliefs, coral reefs are not really exclusive to tropical regions as the Caribbean sea or Australia, they can be also find in cold or temperate water. But it is true that the largest majority come from hot tropicals waters, above 20 meters of depth,  because of the particular life environments they needed. In fact the cold water corals presents different life mechanisms to be adapted to live in cold water and obscurity. In any case, excluding the cold water corals that we will talk about thereafter, coral reefs are mostly found between and in proximity of the two tropics : Tropic of the Cancer  and Tropic of the Capricorn. These regions presents a very high level of insolation,  providing a high sea temperature for corals, in need of a water between 23°C to 29°C to grown optimally. Moreover tropical seas are high-salinity water that is also an important  parameter for coral reefs to extend. The largest coral reefs on Earth are found in three important places : – the Great Barrier Reef is found off coast of Queensland in North-West Australia. It's the largest on earth with 133 000 square miles of coral reef. – in New Caledonia, a little further East – and finally the Belize coral reef, off coast of Belize in Central America. Other regions that include large reefs : the Red Sea, the South-East of Asia (Indonesia), Hawaii, etc... As regards to the particular case of cold water reefs, living between 40 meters and up to 1000 meters deep, in sea water up to a temperature of 4°C, they don't make large structures as the warm water ones. They are smaller, and an important part of these type of  reef are found in Norwegian waters. In fact, few reefs of this type have been found, due to their relative position to the sea level. On a guidance basis, the largest complex found so far  is the Røst Reef, 100 km², in Norway.

How does Global Warming affect coral reefs ? Today, it's proved that the Global Warming is an indisputable actor of coral bleaching episodes ( death of coral reefs and all the species that are related to it ). To answer the question of “how”, it's important to describe the life mechanism of corals species, builder  of coral reefs. Corals live in symbiosis with a microscopic algae : the Zooxanthella. This algae  provide 90% of coral's needs in energy, including glucose, amino acids etc... produced by  photosynthesis. The major benefit for algae is an important hideaway, out of predation, inside the coral tissues. In this way it's easy to understand that this relationship is essential for the coral reefs survival, and obviously for all the species that depend of them. With the increase of temperature in the sea water, caused by global warming, the algae tend to produce a different compound of oxygen called superdioxides. These compounds are highly toxic for corals, which are stressed and expels rapidly Zooxanthella. Then, corals are no longer able to survive due to a lack of energy and begin to die, turning white. This process is called bleaching. Obviously, when the coral dies, all the other species that are related to the reef are affected and eventually disappeared. We then observed, on the reef, an empty space of life, covered  by dead white coral.

How can we help to preserve coral reef ? The more efficient and direct solution must be to stop the increase of sea temperature, which means to block Global Warming by stopping to reject greenhouse gases. But this solution is not really possible because of our dependance to fossil fuels, and it's a global  project, at world level, so very long to process, while coral reefs are an emergency case. A solution can be to rehabilitate coral reefs by “planting” species, artificially, in a protected area or damaged reef. The major problem of this solution is that it's an expensive and very long work, which can only rehabilitate a few number of reefs. An American study suggest that preserve coral reef is a dead end because of the cause, Global Warming, which is too complex to stamp down. This same study observe that an increase of 2°C of sea water temperature will expand the area viable for coral reefs, beyond the tropics, providing new regions with suitable depth and substrate. These regions can be new spaces able to support new coral reefs. Unfortunately, as we see before, coral reefs are very long to build and before that a new coral reef structure is formed, all the pre-existent ones will have disappeared.

Conclusion : Coral reefs are incredible oasis of life. But because of men's activities, its future is widely uncertain. We must, by fair means, find a way to protect coral reefs, otherwise in a couple of decade, or even less, no living coral reefs will remain, marking the largest mass extinction of species in the history of mankind.

Referencing : Wikipedia, Coral reef page http://en.wikipedia.org/wiki/Coral_reef  US Environmental Protection Agency, Coral Reef Article , undated http://water.epa.gov/type/oceb/habitat/coral_index.cfm  NOAA Education Service, Coral lectures, May 2008 http://oceanservice.noaa.gov/education/kits/corals/coral04_reefs.html United Nations Environment Program, Similarities between warm and cold water reef, 2002 http://www.unep.org/cold_water_reefs/comparison.htm Center for Climate and Energy Solution, “Coral Reef and Global Climate Change” article, February 2004 http://www.c2es.org/docUploads/Coral_Reefs.pdf  “Global Warming Effects” on Earth by Abhijit Naik, undated http://www.buzzle.com/articles/global-warming-effects-on-earth.html#Effects-on-CoralReefs The Daily Green, “How to save the World's Coral reefs ?”,8/28/2008 http://www.thedailygreen.com/environmental-news/latest/oceans-acidification-47082802 Western Indian Ocean Marine Science, Rehabilitation of coral reef study, undated http://wiomsa.org/mpatoolkit/Themesheets/H6_Coral_reef_rehabilitation.pdf  http://www.coral-reef-info.com/types-of-coral-reefs.html http://www.coralreefinfo.com/coralreefs/coralreeftypes.htm

The study of science Science is the hangout of knowledge about Earth, Physic, Space, Chemistry... And it's a constant source of discovery. but Science can make also the better and the worst, and there is a lot of examples to discuss on it. First, the good points on science. Thanks to scientific research, impossible feats have  been made possible. Things that were unthinkable a couple of centuries ago are know totally achievable. Walk on the Moon is a very good example. A century before 1969, this idea, concept, was totally out of sense. But because of science and discovery, step by step, the fact to send a man on the Moon began to be real. Thus the study of science permit, more than progress, to achieve our dreams. Moreover, in only a century, the life expectancy have increase of 30 years, from 50 to 80 years ( but only in developed countries ). Thanks to research too, many serious illness and virus have been eradicate, Earth mechanisms have been understand... The list is too long. The service rendered by science are incalculable and sometimes things that appear easy to do or to understand was absolutely not before. But Science has also its flaws. Indeed, science is good when it is well used, which is not always the case, but there not much examples. The most outstanding one might be the nuclear weapon, and it's in fact an interesting case. Because of its power, this weapon can be totally destructive as well as guarantor of peace. In this case, does the science have been well used ? The question remains. I think the study and the use of science is absolutely essential. The benefits that are linked to it are immeasurable. But science must be used in an ethical way, for the health, discovery, security but not for a use based on personal benefits, war or hatred.