When a whale dies and falls to the sea floor, the carcass is a boon to generations of crabs and bone-eating worms and snails, gruesome experiments have revealed. The morbid smörgåsbord could teach us a lot about the evolution of deep sea animals.
By dragging dead whales off beaches, placing them in the depths of the ocean and returning to them year after year, researchers are discovering entire communities of animals that develop on whale carcasses.
New research in California's Monterey Submarine Canyon involving the sunken carcasses of five juvenile whales has turned up more than a dozen new species of bone-eating worms as well as bone-eating snails. The work has also raised the possibility that these small animals are more effective than previously thought at reducing whale bones to dust.
"Original research suggested that the bones would last 50 to 100 years," said Lonny Lundsten of the Monterey Bay Aquarium Research Institute. That would mean the large whale bones would last long enough to serve as artificial reefs for animals that require a harder surface on which to live than the soft sea floor muck.
But the whales Lundsten and his colleagues studied were almost gone in five to seven years, they report in a recent issue of the journal Deep Sea Research.
"What we found is that the reef phase doesn't really exist," said Lundsten.
That said, all the whales in the Monterey study were juveniles. An adult blue whale would have the largest bones and last the longest. "But we still feel that even a large blue whale wouldn't last long."
Another surprise they found is that many of the animals living on the carcasses are not whale specialists -- like the bone-eating worms and snails. Instead, they are just the usual scavengers that are always skittering about in the deep sea looking for manna from above.
"What we found is that most of the animals are background animals" of the submarine canyon, said Lundsten. The whale fall just brings them together. "It's really just a large piece of food."
On the other hand, there are new and unique species of bone-devouring worms, of the genus Osedax, being discovered at whale falls in different parts of the world, said Lundsten. These worms are now known to employ a bacterial symbiont to help them dissolve whale bones.
A newly discovered kind of snail has also been found eating bones, but it is still being studied to find out exactly how it manages to digest the mineralized material. All of these bone eaters form a critical species for making making the whale fall community possible.
How the Osedax worms and snails manage to locate and occupy far-flung whale falls remains a mystery, said Craig Smith of the University of Hawaii, who has studied whale falls off southern California among other places.
"They seem to be finding whale falls very well," Smith said of the worms.
He compares them to other unusual marine organisms face the same problem: the tube worms and other animals that thrive at hot water vents in the ocean floors in widely separate locations worldwide. Like whale falls, these ocean vents are short-lived, which means there much be some way for the animals to disperse and find new homes hundreds or even thousands of miles away.
One thing that might be helping the Osedax worms is that they may be snacking on other kinds of bones between whale falls, said Lundsten. Experiments have now shown that Osedax worms will even eat cow bones, when available.
There might also be a bigger story being told at whale falls and deep ocean vents, said Smith. Perhaps it's whale falls and other large animals deaths over the history of the oceans that have gradually introduced shallow water scavengers into deeper and deeper waters, until they found ways of adapting to things like the hot water vents.
"It just highlights how connected ocean ecosystems are," said Smith.