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Tsunami Clouds Future of Marine Animals

James Owen in London
for National Geographic News
January 17, 2005
 
The depth of human tragedy resulting from the Indian Ocean tsunami disaster is incalculable, even though the scale of visible devastation to coastal towns is now shockingly clear.

But what of marine life? When the tsunami struck, land and ocean merged in a most terrifying way. People and uprooted trees were carried out to sea, while stingrays and sharks were left stranded in fields and parking lots.

The impacts are difficult to gauge. Scientists and conservationists say the future of coastal towns will be closely intertwined with that of fragile marine ecosystems. If coral reefs and mangroves aren't nursed and protected, they say, many human livelihoods will be hard to revive.

The most obvious marine casualties of the tsunami waves were washed up in their wake. In Thailand, for instance, dolphins were swept 500 yards (500 meters) inland. Many dead and injured sea turtles were left high and dry, and a three-foot (one-meter) shark ended up in a hotel swimming pool. Beaches were littered with dead fish as well as human bodies.

And while there are fears for some marine species—such as threatened dugongs and saltwater crocodiles in the Andaman Islands—scientists are most concerned about the habitats these animals depend on.

While it says the overwhelming priority remains the human relief effort, the United Nations Environment Programme (UNEP) has begun to assess environmental damage caused by the tsunami triggered by the massive earthquake off northern Sumatra on December 26.

Early reports indicate that many coral reefs have been extensively damaged, according to Stefan Hain, head of the Coral Reef Unit at UNEP's World Conservation Monitoring Centre in Cambridge, England.

Researchers are particularly worried about the backwash of mud and other debris as the tsunami waves receded. "We have satellite images of regions such as the Andaman and Nicobar Islands which show that a huge amount of sediment and debris has been washed from the land and back into the sea," Hain said.

Turbidity Clouds

Hain said experts are working to determine whether these "turbidity clouds" could smother affected coral reefs.

Coral reefs are highly diverse, complex communities. Reefs are built by coral polyps and symbiotic algae, which need pristine waters to thrive.

"The algae depend on sunlight and, via the algae, so do the corals," Hain added. "If you deprive them of sunlight, it is very difficult for corals to survive. To a certain extent, corals have self-cleaning mechanisms, but we will just have to see whether they will cope with this amount of debris."

Hain said that fish and many other coral reef organisms would have been dislocated and washed ashore by the tsunami, but it is difficult to say how long they will take to recover.

Because corals reefs are among the world's most productive ecosystems, Hain said it's vital that their socio-economic role is taken into account as shattered human communities are rebuilt: "There are millions of people who depend directly on these reefs for food—without them they have no livelihood. As we rebuild coastal zones we have to ensure this is done in a way that will ensure the reefs can still provide these services."

And without coral reefs, the wave of destruction could have been far greater. "Where coral-reef and mangrove ecosystems were intact, we have reports from areas like the Maldives, saying they took the brunt of the wave impact, taking the initial energy away," Hain said. "Lives have been saved."

WWF (World Wide Fund for Nature or World Wildlife Fund) said it has had similar reports from Andhra Pradesh, in southeastern India, where mangroves are credited with saving people who took refuge in them.

"Coral reefs act as a natural breakwater, and mangroves are a natural shock absorber, and this applies to floods and cyclones as well as tsunamis," said Simon Cripps, director of WWF's Endangered Seas Programme.

Turtle Nesting Beaches Vanish

Sarang Kulkarni, a marine biologist with Reef Watch Marine Conservation, based in Mumbai (Bombay), India, is currently in the Andaman and Nicobar Islands. He says the latest generation of leatherback, green sea, hawksbill, and olive ridley turtles has been washed away.

"The nesting beaches in South Andaman, Little Andaman, and the Nicobar group of islands have almost vanished as all these islands have gone down by one to three meters [three to ten feet] due to tectonic activity," Kulkarni said. The turtle nesting season runs from November to January.

Kulkarni said early reports suggest coral reefs were not too badly hit in the Andamans, but he fears widespread damage in the Nicobar Islands, which took the full force of the tsunami strike.

Kulkarni is also concerned for the region's dugongs as these threatened marine mammals are not equipped to cope with violent currents.

"Dugongs are not great swimmers, unlike dolphins, and that is a worry," he added. "The same goes for saltwater crocodiles, as the creeks [where these crocodiles live] also experienced severe impacts."

Given the scale of devastation in the region, Kulkarni said it will take some time before a full environmental assessment can be carried out. Kulkarni said coral reefs and mangroves shield the islands during the seven-month monsoon period.

"Seas are very turbulent at that time," he said. "The reefs and mangroves play a crucial role as a barrier, minimizing the impact of waves on the shore."

Marine Nurseries

Mangroves are tropical, intertidal forests composed of salt-tolerant trees and plants. They support a huge variety of marine organisms and are considered vital nursery areas for many species of fish and crustaceans.

Researchers at the U.S. National Oceanic and Atmospheric Administration (NOAA) in Washington, D.C. said nearshore mangroves, estuaries, and sea turtle nesting areas are likely to have been inundated by the tsunami. They said the impact on organisms that inhabit shallow, inshore environments—particularly those that burrow in seabed sediments—could ripple through the marine food chain for decades.

By contrast, NOAA researchers have found that tsunamis usually do little damage to life in deep ocean waters.

But for coral reefs, the tsunami strike represents the latest of many threats to their survival.

Abnormally high sea temperatures in 1998 affected 75 percent of coral reefs around the world, leading to a condition known as bleaching—the corals eject their life-sustaining algae, causing the corals to turn white.

"If water temperatures remain high for long periods, the corals die," Stefan Hain added.

Hain listed other problems afflicting the coral reefs of the Indian Ocean: overfishing, unsustainable fishing methods involving explosives, soil erosion and sedimentation, coastal development, and reef mining for building materials.

"This is not the first tsunami, and it will not be the last," he added. "What we have to ensure is that the additional pressures on those reefs are reduced, so they can recover and function properly."

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