The wild world of shipwrecks

This month, the US coastguard sank the Japanese vessel Ryou-Un Maru in the gulf of Alaska after she spent nearly a year adrift at sea. She joins three million other shipwrecks on the ocean floor. But are shipwrecks good or bad for marine life?

In 1881, the Kingston set sail from London. The captain and crew believed they were heading for Aden, but the ship never made it past the Red Sea.

On the 22 February that year, she smashed into Shag Rock near the entrance to the Gulf of Suez. The crew were rescued, but the ship sank to the ocean floor.

More than a century on, colourful coral covers the Kingston. The same sponges, tunicates and anemones that live on the adjacent reef are on the wreck. Around 38 species of stony corals and ten soft corals adorn the ship’s surface. In many ways it has become part of the sea floor.

Scientists are now studying the ill-fated Kingston, and other wrecks like her, to gauge their impact on the underwater world they have joined. And different wrecks are throwing up different surprises. While some are literally repulsive to marine life, others are becoming home to new, unexpected communities of animals.

Yehuda Benayahu, professor of marine biology at the University of Tel Aviv has spent much of his career in the Red Sea, examining shipwrecks there.

On old boats such as the Kingston, the wooden parts decay but the steel does not, offering a good foundation for coral. An accidental shipwreck soon becomes an artificial reef, which scientists can analyse.

“Our study in the Red Sea took advantage of the fact that there are seven to 10 different shipwrecks at the entrance to the Gulf of Suez, the date of the tragedy is known, all dated… and all of them are within the depth range of 30 metres and alongside natural reefs,” he told the BBC.

Each ship provides a snapshot in the evolution of an artificial reef after a certain number of decades.

An artificial reef tends only to mimic an adjacent natural reef if there are sufficient structural similarities, his research suggests.

So most shipwrecks are new habitats with distinct communities living in them.

The first organisms to arrive are usually larvae.

“The marine larvae take advantage,” he said. “They start a sort of succession, which means you get different organisms settling with the progression of time.”

Older ships such as the Kingston attract soft corals from the Xeniidae family, research has revealed. Younger shipwrecks tend to attract stony corals from the Poritidae and Pocilloporidae families. It may take several years for these to mature but as they do, the food web expands.

Open water fish are attracted to the reef in search of food. Colourful reef fish such as purple tang arrive seeking food and shelter. Both attract predators such as lionfish.

Military wreck

Eight years ago, an old Royal Navy frigate HMS Scylla was gutted and scuttled off the coast of Cornwall, UK. The project, co-ordinated by the National Marine Aquarium, created an artificial reef in Whitsand Bay. From the beginning scientists observed the wreck monitoring how sea life interacted with it.

There were some big surprises, according to Dr Keith Hiscock, associate fellow at the Marine Biological Association in Plymouth.

“The first two years the colonisation was all over the place… masses of sea urchins, a species we only normally find under boulders on the sea shore, colonised it in vast numbers.

“Then in year two, wrasse arrived and ate the sea urchins,” he said.

An English coral on a nearby reef took almost three years to travel 30 metres to the wreck, but once there spread prodigiously and unexpectedly quickly.

Pink seafans on the wreck are also growing surprisingly fast, said Dr Hiscock. They were thought to grow about one centimetre a year, but some have grown 40cm in just a few years, he explained.