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First bone-eating worm found in warm waters
Museum scientists have found that Osedax worms, which feed on the bones of whale carcasses, can live in shallow Mediterranean waters.
Until now, it was thought that the worms could only live in colder waters, such as the Southern Ocean around Antarctica, or deep below the surface.
But scientists have found a previously unknown species, provisionally named Osedax 'mediterranea', off the north-eastern coast of Spain.
It was living on a minke whale bone planted by the team 53 metres below the surface. The water there can reach 12 to 22°C, which is far warmer than the -1 to 15°C of other shallow-water Osedax habitats.
'We were lucky to find the worm there,' says Dr Sergi Taboada, who led the study. 'Most of the time, bones in warm water decompose before Osedax have a chance to feed on them.'
Unusual lifestyles
Osedax worms, whose name means bone-eating in Latin, were first discovered off the coast of California in 2002, feeding on the carcass of a gray whale.
Their behaviour has earned them the nickname zombie worms.
Lacking a mouth, they use acid to bore into the bone, and without a digestive system they rely on symbiotic bacteria to break down the nutrients into a form they can absorb.
This female Osedax specimen shows the root tissues usually hidden within the bone the worm is feeding on
Only female worms drill for food - the microscopic males live in tubes inside the females, ready for when the time comes to fertilise their eggs. When the next generation of larvae are released, they drift through the water until they find a suitable new bone habitat to settle and feast on.
Early evidence
Since 2002, several Osedax species have been found in locations across the Pacific, North Atlantic and Southern oceans, at depths of up to 3,000 metres. This is the first time that the worms have been found in warm, shallow waters.
Although the Mediterranean Sea might seem like an unusual place to search for a worm thought to live in cold water, there was evidence that Osedax worms could survive in the area - at least historically.
In 2012, Museum scientists found bore-holes in a three-million-year-old whale bone that had once lain 90 metres below the surface of the sea, in an area that is now part of Italy.
More to find
Dr Taboada's initial experiments in the Mediterranean failed to find any sign of Osedax activity. He believes that this is down to the depth of the bones, and the local sea currents.
'We tried placing bones 20 metres below the surface, but didn't find any worms there,' he says.
'Eventually we tried deploying the bones deeper, 50 metres below the surface, near the head of the Blanes submarine canyon.
'This area is influenced by the colder, deeper waters of the canyon, which probably helped the bones survive for as long as possible.'
The team found the Mediterranean Osedax living on mammal bones they'd left near a submarine canyon off the coast of Spain
Given the worm's location, and the fossil found in Italy, the scientists believe that its ancestors reached the Mediterranean around five million years ago, after the Strait of Gibraltar opened up the sea to water from the Atlantic.
They now plan to continue their search for Osedax in the Mediterranean, starting with the Blanes canyon.
'We think that the Osedax we found came from the canyon,' explains Dr Taboada.
'This means that there could be whole populations living deep in the canyon, and we're planning to do more experiments there very soon.'