Reefs in trouble

Conservation

Animal, vegetable and mineral, a pristine tropical coral reef is one of the natural wonders of the world. Bathed in clear, warm water and thick with a psychedelic display of fish, sharks, crustaceans and sea life, the coral ramparts that rise from the sand are known as the rainforests of the oceans. And with good reason. Reefs and rainforests have more in common than their beauty and bewildering biodiversity. Both have stood for millions of years, and yet both are poised to disappear.

Doomed reefs

Coral reefs are doomed. The situation is hopeless. Forget ice caps and rising sea levels: the coral reef looks like it will enter the history books as the first major ecosystem wiped out by our love of cheap energy.

A report from the Australian government agency that looks after the nation’s emblematic Great Barrier Reef reported that “the overall outlook for the reef is poor and catastrophic damage to the ecosystem may not be averted”. The Great Barrier Reef is in trouble, and it is not the only one.

Within just a few decades, experts are warning, the tropical reefs strung around the middle of our planet like a jewelled corset will reduce to rubble. Giant piles of slime-covered rubbish will litter the sea bed. “The future is horrific,” says Charlie Veron, an Australian marine biologist regarded as the world’s foremost expert on coral reefs.

Alex Rogers, a coral expert with the Zoological Society of London, talks of an “absolute guarantee of their annihilation.” And David Obura, another coral heavyweight and head of CORDIO East Africa, a research group in Kenya, is equally pessimistic: “I don’t think reefs have much of a chance. And what’s happening to reefs is a parable of what is going to happen to everything else.”

Of the billions of tonnes of carbon dioxide spewed from cars, power stations, aircraft and factories each year, about half hangs round in the thin layer of atmosphere where it traps heat at the Earth’s surface and so drives global warming. What happens to the rest of this steady flood of carbon pollution? Some is absorbed by the world’s soils and forests, offering vital respite to our overcooked climate. The remainder dissolves into the world’s oceans. And there, it stores up a whole heap of trouble for coral reefs.

Often mistaken for plants, individual corals are animals closely related to sea anemones and jellyfish. They have tiny tentacles and can sting and eat fish and small animals. Corals are found throughout the world’s oceans, and holidaymakers taking a swim off the Cornish coast may brush their hands through clouds of the tiny creatures without ever realising.

It is when corals form communities on the sea bed that things get interesting. Especially in the tropics. In the turquoise waters of the Caribbean, Indian Ocean and Pacific, the coral come together with tiny algae to make magic.

Symbiosis

The algae do something that the coral cannot. They photosynthesise, and so use the sun’s energy to churn out food for the coral. In return, the coral provide the algae with the carbon dioxide they need for photosynthesis, and so complete the circle of symbiotic life.

Freed of the need to wave their tentacles around to hunt for food, the coral can devote more energy to secreting the mineral calcium carbonate, from which they form a stony exoskeleton. A second type of algae, which also produces calcium carbonate, provides cement. Together, the marine menage-a-trois make a very effective building site, with dead corals leaving their calcium skeletons behind as limestone. For all their apparent beauty and fragility, just think of coral reefs as big lumps of rock with a living crust. A fragile crust too. The natural world is a harsh environment for coral reefs. They are under perpetual attack by legions of fish that graze their fields of algae. Animals bore into their shells to make homes, and storms and crashing waves break them apart. They may appear paradises, but most coral reefs are manic sites of constant destruction and rebuilding.

Warming worsens scenario

Global warming, predictably, has made the situation worse. Secure in their tropical currents, coral reefs have evolved to operate within a fairly narrow temperature range, yet, in the late 1970s and 1980s, coral scientists got an unpleasant demonstration of what happens when the hot tap is left on too long. “The algae go berserk,” said Rogers. Scientists think the algae react to warmer water and increased sunlight by producing toxic oxygen compounds called superoxides, which can damage the coral. The coral respond by ejecting their algal lodgers, leaving the reefs starved of nutrients and deathly white. Such bleaching was first observed on a large scale in the 1980s, and reached massive levels worldwide during the 1997-98 El Niño weather event.

The mass bleaching event that followed killed a fifth of coral communities worldwide, and though many have recovered slightly since, the global death toll attributed to the 1997-98 mass bleaching stands at 16 per cent.

Can the coral be helped? Off Japan, scientists are farming healthy coral on hundreds of ceramic discs, which they plan to transplant onto the badly-bleached Sekisei Lagoon reef within two years. In 30 years or so, they hope the reef can recover fully.

A similar exercise is under way in the Philippine coastal community of Bolinao, where local people have broken off chunks from the healthy section of their local reef and have crudely wedged them into cracks in bleached sections. Others have cultured corals in swimming pools, and researchers in the Maldives are using giant sunken cages, connected to a low level electric current, to help coral form their chalky shells.

IN THE RED

* The algae do something that the coral cannot. They photosynthesise, and so use the sun’s energy to churn out food for the coral.

* Freed of the need to wave their tentacles around to hunt for food, the coral can devote more energy to secreting calcium carbonate.

* The mass bleaching event during the El Nino weather event killed a fifth of coral communities worldwide.