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Science & Hi Tech: North Sea rigs offer coral oasis in the mud

Posted on 15.03.2006 - 01:52 EST in SCIENCE & TECH NEWS by Rons_ROV_Links

Lophelia pertusa cold water coralOil and gas platforms abandoned at the end of their lives have become a breeding ground for marine wildlife, says Roger Highfield.

The platform stands as tall as the Canary Wharf tower and has reached the end of its working life in the North Sea. But rather than being yesterday's eyesore and bane of the environment, this hulking structure could be tomorrow's ecological darling.

Since the late 1940s, thousands of rigs have been planted in the world's shallow seas, with around 300 offshore installations in the unforgiving waters around the UK. Over the past decade, however, evidence has emerged that they are habitat forming.

Among those studied by marine scientists is BP's vast North West Hutton platform, which started to produce oil and gas more than two decades ago and has now reached the end of its life.

A convention has ruled that these structures must be completely removed. But this particular platform is so huge - standing 240 metres tall in 140 metres of water - that an exemption can be applied for and BP hopes (a Government decision is expected soon) to spend £160 million to remove most of the platform.

The remains of this 40,000-ton structure will provide the first artificial reef of its kind in the North Sea, an oasis on the sea bed, where life is relatively sparse.

Perhaps the most remarkable inhabitants of the platforms are corals, which most people associate with well lit, clear blue tropical waters, not the turbid waters in permanently dark waters deep in the north-east Atlantic. The commonest is Lophelia pertusa.

Like other corals, they consist of tiny animals - polyps - that use their tentacles to catch food particles floating in the water and, unlike their tropical peers, do not rely on algae to harness sunlight for energy. They also produce calcium carbonate skeletons - which grow into the framework of the coral reefs.

Coral larvae need a hard surface where they can settle, creating a strong attachment point for a new colony. Most of the North Sea bed is unsuitable for reefs - the bottom is muddy and has few rocky areas. But the oil and gas platforms are ideal platforms for corals. In turn, the reefs provide critical habitats for a multitude of other aquatic animals.

This deep-water coral supports a diverse community of sponges, seamats (bryozoans), anemones, bristle worms, crustaceans - the list goes on. As they flourish, they provide food and hiding places for little fish, which in turn provide food for bigger fish, building a diverse and complex habitat.

Ironically, the role of the rigs in hosting coral was revealed when decommissioning the Brent Spar oil rig in 1999, the subject of a long battle between the industry and environmentalists. Europe adopted a policy of removing rigs, rather than toppling them to make artificial reefs as is done in the Gulf of Mexico, because of environmental concerns about the debris that is left.

Surprised workers spotted Lophelia pertusa colonies on the Brent Spar structure. No one expected this cold-water coral would turn up on oil rigs. "This was good for us, since the rig provided an accessible environment," said Susan Gass, who has been surveying the rigs with Dr Murray Roberts of the Scottish Association for Marine Science in Oban.

Lophelia pertusa cold water coral

Lophelia coral has been found on 14 oil platforms
around the UK, at depths of up to 150 metres

More of the bright orange and white corals turned up in the Beryl oil field. And, after delving into the video libraries the oil and gas companies collect during their maintenance surveys, Lophelia was found on 13 more platforms, at depths of up to 150 metres. It was also possible to assess their growth rates.

The discovery of this new habitat is all the more surprising, since such hard corals have long been considered vulnerable to chemical contamination and oily discharges from oil wells and susceptible to being smothered by the discharges of sediment from the surface, when muds and cuttings are returned to the waters.

Gass is trying to find out how they cope, studying the corals with the Subsea7 remotely operated vehicle and using it to recover samples from the well conductors and the North West Hutton platform structure.

She has removed samples from the platform to grow in the laboratory to see how the polyps respond to various kinds of pollution. "As the coral colonies are not on the seabed, they are above sediment build-ups and have good water flow around them," she said.

Unusually for the North Sea, they were able to use the remotely operated sub in the winter, providing a rare opportunity to study coral during spawning. "This really helped to fill in details of its reproductive cycle."

North West Hutton should be gone within a few years. Toppling rigs is barred in Europe by the Ospar convention, which considers it dumping - it is concerned about the likely impact of disturbing drilling muds and oils. But the plan with North West Hutton is to begin in the next year or two to remove the topsides and steel jacket down to the top of the footings (the base of the jacket) for recycling onshore.

Because of the safety risks and technical uncertainty the decomissioning engineers face, they plan to leave in place the jacket footings - the four legs that it stands on, including the steel piles which are driven into the seabed.

In this way, the biggest rigs such as North West Hutton and Frigg could help to reverse a worrying trend seen since the Lophelia was first discovered, when fishermen brought corals up in their nets in the 18th century.

Many reef areas are being damaged by fishing, especially bottom trawling, which is destroying habitats that are thousands of years old.

In a small way, oil industry has helped reverse that decline.

March 14, 2006

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