DSCC News

These Deep-sea Creatures Have Existed For 10,000 Years

1 November 2016

Source: BBC – Melissa Hogenboom

Off the north-west coast of Scotland, 3,300ft (1,000m) under the sea, life is thriving amidst an otherwise drab and muddy ocean floor.

This is thanks to a cold-water coral system called the Darwin Mounds. Unlike their tropical counterparts, these corals do not need sunlight to survive. Instead they sit in the dark, waiting for food to pass by.

As they are so deep, these corals are not easily visible. In fact, until 1998, no one even knew this group of corals existed. They are also extremely fragile: easily damaged and even destroyed by the deep-sea fishing trawlers that drag their nets along the ocean floor. The reef structures, which can take thousands of years to grow, can be killed in mere moments.

"If all the 'parent' coral colonies are damaged, they will not easily produce offspring, and it becomes very difficult to have new coral colonies establishing," says Veerle Huvenne of the National Oceanography Centre (NOC) in the UK.

This is why they need to be protected. But although the Darwin Mounds are now well recognised, there are believed to be many more cold-water corals off the UK coast that remain undiscovered. How can an area deep under the sea be protected if nobody knows it is there in the first place?

 

A large school of fish use these cold-water corals on Rockall Bank for shelter

A large school of fish use these cold-water corals on Rockall Bank for shelter (Credit: National Oceanography Centre)

 

The corals are important as more than oddities: they provide the ideal place for small sea life. There are numerous niches, crevices and holes where animals can hide, explains Huvenne. They are "little islands of high biodiversity". In fact, one mound can be home to as many as 1,300 different types of marine life.

Coral reefs are also places where mothers rear their young fish. "We saw cold-water coral reefs teeming with pregnant fish – ready to span," Huvenne says of one expedition.

Corals also offer glimpses into the past. By drilling into coral mounds, the lowest parts of which are the most ancient, scientists can get an idea of the sea's condition when the corals were first growing.

For instance, the Darwin Mounds have existed for about 10,000 years, ever since the end of the last ice age. That means they could tell us how the sea has changed since then.

"During glacial times, the water masses, temperatures and primary productivity at surface were very different to what it is now. It's only when Earth started warming again that we could have these coral reefs in this area," says Huvenne.

 

Black coral on Anton Dohrn seamount (Credit: Deep Links Project)

Black coral on Anton Dohrn seamount (Credit: Deep Links Project)

 

As important as they are, cold-water corals are not especially rare. They are found in waters from Norway to northern Africa. But their depth means they can go undetected for years.

The existence of deep-water corals in UK waters will have been known to fishermen since at least the 1700s. But for decades, no one knew just how many existed in the seas surrounding the UK. Then in 1998, the National Oceanography Centre's (NOC) Brian Bett led a large-scale environmental survey.

"I was sent a fax of a hand-written sketch saying 'there's something interesting over there,'" recalls Bett. Armed with the clue, he dropped a camera down into the waters below the area.

n doing so, he discovered the Darwin Mounds: the UK's largest cold-water corals. They are spread over a total area of 39 square miles (100 sq km). The corals that made them belong to the species Lophelia pertusa, which is the main coral in British waters that forms reefs.

Two years later, Bett came back for a more extensive survey – and to his horror he found that some of the corals had experienced significant damage. Deep-sea trawlers were to blame: there were tell-tale linear grooves on the sea bed from where their nets had scraped over it. To prevent further damage, the UK Government, acting through the Joint Nature Conservation Committee, used the evidence collected by NOC scientists to arrange for the site to become a marine protected area.

But Bett knew a deep-sea fishing ban would also need to be enforced. "There's no point in having a protected area without a ban on bottom fishing," he says. It took more than three years to enact.

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