Bleached coral: Mandapam coast, Gulf of Mannar. Photo: A. Shaikmohideen

Coral reefs are not only beautiful, they also support a wide variety of sea life. If you take away these reefs, life in the sea would get disrupted.

Many of us may have corals at home, collected after a trip to the ocean side. Of course, they aren't something to be picked off the beach like a sea shell! You may have found some, in their fascinating shapes, lying around. And that's where the story begins.

Picture postcards and television channels often have pictures and images of coral reefs, in many magnificent colours, supporting a whole variety of sea life, and of divers exploring reefs while being encircled by hundreds of species of fish. Take away these reefs and life in the sea would get disrupted. They have even been called as “the rainforests of the seas”.

Have you ever thought about coral reef pollution? Marine scientists say that a quarter of the world's total coral reefs have vanished. Pollution, over fishing and reef disease are the reasons.

Contamination

Scientists have found that pollution in rivers is a major factor affecting reefs. The chemicals and fertilizer used on farmland drain into rivers.

For example, a study of the Mississippi, which flows down into the Gulf of Mexico, showed how it affects the Belize Reef. Pollutants from as far as Minnesota, Wisconsin, Iowa, Illinois, Missouri, Arkansas, Tennessee, Mississippi, and Louisiana joined the river before ending up in the ocean.

And then there is overfishing, where fish are lost in large numbers. Fishermen use explosives like dynamite to get the fish they want and destroy vast areas of coral. Human waste from coastal resorts also cause damage. Algae (which help coral live) proliferate in large numbers. This is because phosphate levels in waste water disrupt the chemical balance needed for coral to live. Phosphates help algae to overbloom so it almost suffocates coral colonies making it harder for them to recover from storms or disease.

The naturalist, Sir David Attenborough, has warned that global warming is another danger. “Global warming means warmer seas, which causes the corals to bleach, where the creatures lose some of the algae they need to survive.” Carbon dioxide plays a part in making sea water more acidic. When this happens, the structure of corals, or their exoskeletons, starts to dissolve. He adds: “They are the places where the damage is most easily and quickly seen. It is more difficult for us to see what is happening in, for example, the deep ocean or the central expanses of ocean.”

There is also a new factor of pollution. Noise. A study this year, by the University of Bristol, U.K., has shown that young corals, in their initial days as larvae, find their way by listening to the noise of animals that live in the reefs.

But human noise pollution from ship engines, to oil drilling to underwater exploration is blocking off these sounds and in turn affecting coral.

Artificial reefs

You may have seen pictures of cars, trains or even old ships being deliberately sunk. The idea is to create an artificial reef and form an area for marine life to survive. Other material used in such projects are PVC and concrete structures. Old shipwrecks also become sites. In 2002 and 2006, and after “environmental preparation”, the U.S. warships, the USS Spiegel Grove and the USS Oriskany, were sunk off the coast of Florida to create reefs.

What are coral reefs?

By definition, a reef is not a rock-formation, but a structure made up of calcium carbonate that coral polyps produce. They live and grow in the middle of this structure and attract a variety of marine life, forming vital breeding areas. They form a separate ecosystem on this planet. It is these polyps that also give the reefs their brilliant colours, attracting tourists and helping marine tourism.

Scientists add that in many cases, most of these reefs were formed during the last glacial periods, which means that they go back in time to thousands of years.

Where are the largest reefs found?

Around America, Asia, Africa and Australia. But the largest of them all is Australia's Great Barrier Reef. The second largest is said to be the Belize Barrier Reef that starts from Mexico all the way to the Bay Islands of Honduras.

In the case of these two examples, they are near human habitation, which means that there is the problem of pollution. The coast attracts tourism. Resorts and houses are built. All this means that waste water, pesticides and petroleum products find their way into the ocean as run-off.

David Attenborough : “Anybody who has had the privilege of diving on a coral reef will have seen the natural world at its most glorious, diverse and beautiful. There is a moral responsibility one has to the natural world. Also you have responsibility to future generations, to your future grandchildren and great grandchildren.”

The Hindu