Expert sounds coral reef alarm bell

Park Street: Coral reefs all over the world, including in India, are staring at extinction because of global warming and other threats, a scientist recently said in Calcutta.

The natural marvels that dates back 250 million years have survived multiple mass extinctions but human activities are proving a greater threat, Ch. Satyanarayana, a coral taxonomist and conservationist with the Zoological Survey of India, said.

He spoke on the threat to coral reefs at a session hosted by the Indian Museum on Wednesday.

A coral reef is a marine ridge or reef of coral and other substances, the top of which is usually just above or just below the surface of the sea. The diverse underwater ecosystem is held together by calcium carbonate structures secreted by corals.

Coral reefs are the most diverse of all marine ecosystems. Teeming with life - fish, jellyfish, crabs, shrimps, lobsters, turtles, sea snakes, snails, and molluscs, to name a few - the reefs provide food and shelter to a quarter of all ocean species.

This is despite the fact that reefs cover just a fraction of the earth's surface and less than two per cent of the ocean bottom.

Coral reefs are often called the rainforests of the sea because of their diversity. The reefs account for more than 25 per cent of the world's total fishery yield.

"Corals have the distinction of building the largest structure on earth made by living organisms - the Great Barrier Reef in Australia, which is larger than the Great Wall of China," Satyanarayana said.

The major reef regions in India are the Andaman and Nicobar and Lakshwadeep islands and the Gulf of Mannar, Palk Bay and Gulf of Kutch.

India has the 10th largest reef area in the world, spanning 5,790sq km.

But global warming, pollution, mining, large-scale fishing and uncontrolled tourism are taking a toll on the reefs.

Coral bleaching is one of the worst dangers to the marine ecosystem, the scientist said. Overheated seawater leads to corals expelling the symbiotic algae living in their tissues, causing them to turn pale, hence the term bleaching. Bleaching makes the corals more susceptible to death.

"When a coral dies, the shelter that sustains fish and hundreds of other organisms is gone. So, the entire ecosystem is in danger," Satyanarayana said.

By 2000, close to 27 per cent of the world's reefs had died from bleaching, Satyanarayana said. "The number could be 60 per cent by 2030. By 2100, most of the coral reefs would be gone if we don't act now."

In India, recent studies have shown that the Kutch reefs are in bad shape while Andaman reefs are reasonably healthy, the scientist said.