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coasts and oceans > features > ancient coral reefs under attack

Ancient coral reefs under attack

Posted: 19 Jun 2003

by Joanna Benn

Imagine a giant bulldozer crashing through the Amazon rainforest, demolishing trees, crushing animals, destroying living systems that are thousands of years old, all in a matter of hours. The equivalent of this is happening on the deep ocean floor, to ancient coral reefs whose mysteries are only just beginning to be revealed. Joanna Benn reports.

These are not the tropical reefs that we are all familiar with, but cold-water coral - living as deep as 2000m below the ocean surface, well beyond the reach of sunlight and where the temperature can be as low as 4°C.

Cold-water coral reefs are home to:: a wide variety of other species.:: Selligrunnen reef, Trondheimsfjorden, Norway.::© WWF/Erling Svensen
Cold-water coral reefs are home to
a wide variety of other species.
Selligrunnen reef, Trondheimsfjorden, Norway.
© WWF/Erling Svensen

Despite their dark, chilly location, these reefs are every bit as beautiful as their tropical counterparts. The Lophelia pertusa reefs off the coasts of Scotland, Ireland, and Norway, for example, grow as delicate branches ranging in colour from orange to pink to white. Like tropical reefs, they are home to a multitude of other animals, including starfish, sea urchins, anemones, sponges, worms, and crabs. They are also likely to be important spawning and nursery grounds for several fish species, including commercially valuable ones.

Ancient ecosystem

Their biology is, however, very different. Tropical corals get most of their food from symbiotic algae, which create energy from photosynthesis. Sunlight doesn't reach the areas where cold-water coral grows, so instead, these corals feed by capturing microscopic organisms and food particles that drift past. Cold-water corals are also incredibly slow growing: it can take 400 years for coral tree to become just 2cm thick. The largest reefs discovered so far are up to 3km wide and 45km long and are at least 4,500 years old - amongst the oldest living systems on the planet.

Although fishermen have known of their existence for a long time, it's only in the last decade or so that scientists have really started to study cold-water coral. They have been found around the world, from the Bering Sea and northern Europe to Florida, the Galapagos Islands, the southern Pacific, and even Antarctica. Most deep-water reefs are poorly mapped, and it's likely that many more remain to be discovered. Many mysteries remain even for the best-studied reefs, including the details of how the corals feed and reproduce.

Alarmingly, the chance to investigate these unique ecosystems further is disappearing.

Trail of destruction

Industrial trawlers, whose huge nets capture nearly everything in their path, once avoided coral reefs and other rocky regions of the ocean floor because their nets would snag and tear. But the introduction of rockhopper trawls in the 1980s changed this. These trawls are fitted with large rubber tires or rollers that allow the net to pass easily over any rough surface. The largest, with heavy rollers over 75cm (30 inches) in diameter, are very powerful, capable of moving boulders weighing 25 tons. Now, there is virtually no part of the ocean floor that can't be trawled.

Smashed and dead cold-water coral::fragments in a trawling ground on::the Norwegian continental shelf.::© Institute of Marine Research, Norway
Smashed and dead cold-water coral
fragments in a trawling ground on
the Norwegian continental shelf.
© Institute of Marine Research, Norway

Not surprisingly, these trawls - whose use is now widespread - are extremely damaging to fragile and slow-growing structures like coral reefs.

"Rockhopper gear smashes reefs and other vulnerable habitats and species," says Dr Jan Helge Fosså from Norway's Institute of Marine Research. "Bottom trawling is the worst threat against biodiversity in the deep sea."

In an experiment off Alaska, 55 per cent of cold-water coral damaged by one pass of a trawl had not recovered a year later. Scars up to four kilometres long have been found in the reefs of the north-east Atlantic Ocean. And in heavily fished areas around coral seamounts off southern Australia, 90 per cent of the surfaces where coral used to grow are now bare rock.

Ghost gillnets - fishing nets that are set near coral reefs but are lost or abandoned - are also a problem. These nets can snag on the reefs and continue to trap and kill whatever swims into them, and are difficult to retrieve without further damaging the reef.

Scientists fear that trawling and other fishing damage has already destroyed 30-50 per cent of cold-water coral off Norway's coast. The global percentage could be similar, with other deep-sea habitats also affected. On top of this, marine pollution and oil and gas exploration may also be affecting deep-sea habitats.

Destroying habitats

The loss is not only a biological one. Cold-water corals are important habitats for already overexploited fish populations. Loss of fish nurseries through reef destruction translates into economic loss for the fishing industry. This loss could also affect food security.

"Much attention has been focused on the protection of tropical corals for their importance to fisheries, biodiversity, and for the economic benefits they bring to people, but cold-water corals are by no means less important," says Dr Simon Cripps, Director of WWF's Endangered Seas Programme. "Increased research and better protection are urgently needed to prevent these fragile and slow-growing habitats from being irreparably damaged."

Thanks to the work of different scientific institutions that have helped raise awareness of the importance of cold-water corals, some progress has been made towards protecting these valuable areas. Earlier this year, the US introduced a new law that limits rollers and tires on rockhopper and other bottom trawl gear to 20cm (8 inches) in diameter. And just last week, Norway announced protection measures for the newly discovered Tisler Reef, bringing the total number of protected Norwegian deep-sea reefs to five.

But more needs to be done. Despite Norway's global leadership, the overwhelming majority of countries have not implemented any protection measures for cold-water corals. WWF, the global conservation organisation is calling for marine protected areas (MPAs) to be established around the world to protect cold-water coral reefs - as well as tropical coral reefs and other vulnerable marine habitats - where damaging bottom trawling activities should be prevented.

Good topographical maps of the ocean floor are also needed so that other types of fishing can avoid cold-water coral. In addition, more information is needed in general about these ecosystems so that they can be better monitored and managed.

"Cold-water corals are not only extraordinarily beautiful, but also important for the biodiversity of the deep sea," says Jan Helge Fosså. "And there's still so much to discover about them. Damaging bottom trawling must be stopped in areas where these corals live - if we destroy the reefs, then they're gone forever..."

Joanna Benn is TV Producer at WWF International.

Related links:

WWF's Coral initiative

WWF's work in the north-east Atlantic

Information on marine habitats in the north-east Atlantic

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