As it decays, a whale carcass can sustain whole communities of living creatures.© Craig Smith and Mike Degruy
And while it’s an adventure that most of us would not even contemplate undertaking, it’s one that has been casting a fascinating light on a hitherto unimagined world beneath the waves. For Smith’s studies are showing that, in death, whales give life, their giant, slowly decaying carcasses supporting communities of fauna that make so-called "whale falls" among the most diverse habitats in the deep sea.
After sinking a whale (or discovering a naturally existent whale fall: the former is necessary largely because the latter are tough to locate), Smith returns to it periodically. With one skeleton, he set up a time-lapse camera, which took photographs of the community for eight months. Unfortunately, the camera was a little too close to the carcass and the view was obscured by pieces of blubber. Normally, however, he utilizes either remote-operated vehicles (ROVs) or manned submersibles, studying the whale fall fauna in situ and also removing samples to the surface for closer inspection.
According to Smith, a single whale fall can apparently support a community of up to 200 species for as long as 50 to 100 years. Some are scavengers—hagfish, crustaceans, sharks—which devour much of the whale’s flesh and tissue over the course of a few months. Others use the substrate of the skeleton for suspension feeding. Still others—worms, clams, mussels, among others—take advantage of the sulfide-rich environment created by the steady bacterial decomposition of lipids in the whale’s bones.
Remarkably, some of this latter group appear to have evolved specifically to take advantage of whale carcasses: among them, an entirely new genus of worm, Osedax, which has no mouth and no stomach, but uses a chemical delivered through a root system to dissolve and burrow into the bone. Symbiotic bacteria in its tissues then digest the marrow’s oils and fats.
So far, says Smith, he and his colleagues have identified a total of 400 species living in the five whale fall communities that his team has either discovered or sunk in a small area off southern California. Thirty-two appear to be unique to whale falls. Furthermore, other teams of researchers have also begun sinking whale carcasses—off northern California, off Japan, and in the Atlantic—and have identified their own unique species. "I wouldn’t be surprised," says Smith, "if the amount of whale fall specialist [species] got up into the hundreds as we increase our studies."
Unfortunately, whale carcasses are not as common on the sea bed as they used to be. Centuries of intensive commercial whaling have seen to that. "In the North Atlantic, for example, levels of great whales are no more than 25 percent of their original populations," says Smith.
Amy Baco-Taylor, a visiting investigator at Woods Hole Oceanographic Institution who wrote her thesis on whale falls, says that removing these carcasses would cause a high number of extinctions. "These communities are pretty important in the deep sea. Each individual whale fall has species that we haven’t seen yet, so there’s obviously a very high level of diversity. There are almost as many species on whale falls as have been found on hydrothermal vents, which have been studied for a lot longer."
Professor Steven Palumbi of the Hopkins Marine Station at Stanford University says whale falls reveal "another link in the great ocean food chain. The ocean bottom is one great recycling center. It’s a little scary to think that we are capable of reaching that far down and affecting the wiring."
It will be some time before Smith and colleagues come close to determining how many whale fall specialist species there may be in the ocean. They will only ever be able to speculate how many there once were, and how many were eradicated by the ravages of whaling.