Moveable Feast

When dead whales sink to the ocean floor, they give life to an array of bizarre creatures—including gutless, bone-devouring worms.

A community of organisms surrounds the skeleton of a gray whale that has been on the seafloor for six years
Credit: Photo: NOAA

When Shannon Johnson talks about cleaning out her freezer, the picture she paints is less Betty Crocker and more Dexter. Disposing of the stockpile of bones she kept on ice, she explains, requires saws and drills. And disposable clothing. “It gets messy,” she says. “It’s gross, and you do not want to wear those clothes ever again.”

Johnson has a professional obsession with death. Or, more accurately, life after death. She is a molecular ecologist from the Monterey Bay Aquarium Research Institute who study whale falls—the nutrient-rich feasts that abruptly appear when leviathans die and sink to the barren seafloor.

The macabre buffet can support an array of creatures for decades. In fact, hundreds of animal species have been documented at whale falls, rivaling the biodiversity seen at hydrothermal vents (though there are concerns that whaling has wiped out some of these whale fall specialists).

After a whale perishes, hagfish, sleeper sharks, and other scavengers rip into its fresh flesh. Then come opportunistic worms, mollusks, and crustaceans to strip the bones clean. The feeding frenzy doesn’t stop there. Anaerobic bacteria dine among the decaying bones; some of these microbes form lush mats that offer nourishment to other creatures, while others live as symbionts within other organisms—including freakish worms with bright red plumes that grow roots into the behemoth’s bones to excavate the lipids. The genus of worms, named Osedax, Latin for “bone devourer,” was only first described in 2004, but their odd sex lives, remarkable diversity, and mysterious movements have made these tiny, gutless, mouthless wrigglers the superstars of whale fall research.

Osedax, bone-devouring worms, thriving on grey whale’s phalange, or finger bone, in a tank in Scripps scientist Greg Rouse’s lab.
Credit: Photo: Greg Rouse/Scripps Institution of Oceanography

Of course, to study Osedax, first you have to find them. Tens of thousands of whales die each year, yet the chances of locating a single carcass in the vast watery expanse are slim. So Johnson and others often make their own whale falls. Under the leadership of evolutionary biologist Robert Vrijenhoek, they’ve sunk several whale carcasses and bones (hence the frozen stockpile) at depths ranging from about 1,000 to 10,000 feet in Monterey Canyon over the past decade, but little remains of the former giants, which washed up dead onshore. “All of the Monterey Bay whale falls are basically brown spots, just mud,” says Johnson. “The worms have been so voracious they’ve almost eaten all the bones.”

In that time, researchers in Monterey Bay and across the globe have discovered how Osedax get to the juicy fats locked inside bone (they secrete acid); that females acquire harems of dwarf males after they settle down on the bones (the guys take up residence inside the ladies and basically just serve as sperm factories); and that these worms are surprisingly diverse and widespread. They’ve been found in shallow waters off the coast of Sweden, Antarctic waters, and off the coast of Japan—in fact, says Johnson, they’ve found some of the same species of Osedax at Japanese and California whale falls. “That is amazing,” she says. “That’s incredible dispersal ability.”

Johnson and others have discovered that Osedax will feed on bones from creatures other than whales—even landlubbers. They’ve taken up residence on cow and fish bones scientists left on the seafloor, and researchers recently discovered that this rapacious annelid would feed on the bones of marine-dwelling plesiosaurs and sea turtles 100 million years ago. But, Johnson and colleagues wondered, given the choice, do the annelids prefer whale bones?

They got the chance to find out at the whale fall of a longtime collaborator Greg Rouse, a marine biologist at the Scripps Institution of Oceanography. He had sunk a 20-ton, 75-foot-long fin whale off San Diego. (FYI: To settle the giant, which had been killed by a boat collision, under nearly 3,000 feet of water, they had to tow her out 12 miles and then attach nearly seven tons of metal to her.) In addition to the whale, they placed an array of animal remains on the seafloor. “We have a picture of a pig with an apple in its mouth on the bottom of the ocean,” says Johnson. “And a turkey suspended in the water.” But the most exciting aspect was a camera focused on bones from cows, elephant seals, and whales that Johnson had zip-tied to a platform.

When they picked up the camera in June 2014, it held six months worth of photos of Osedax activity. Typically, researchers are only able to visit whale falls—via ROVs they launch from a research vessel—once a year or so, so the photographic documentation of daily happenings was unprecedented. They discovered that “whale bones do get colonized just a tiny bit faster,” says Johnson, within about a month. She’s currently writing up the results for publication.

Rouse’s morphological investigations, meanwhile, have shed light on the worms’ reproduction and how these tiny invertebrates are able to find isolated islands of bones in the vast ocean. “The female is about one-third ovary, so she’s just constantly making lots and lots of eggs, 400 to 800 per day on average,” says Rouse. “That huge fecundity, combined with larvae that live for weeks and weeks, passively floating—that makes them successful.”

Rouse, Johnson, and colleagues are digging deeper into the different species of Osedax along the Pacific coast. Rouse spearheads much of the work into Osedax biology and evolution, while Johnson handles most of the population genetics analysis. So far, they and their colleagues have found 18 species of Osedax in Monterey Bay, 14 of which have not yet been named. Some are so similar that Rouse says only genetics can tell them apart.

That, however, isn’t the case with a species that he discovered recently. In a tank in his office, Rouse was housing an Osedax-covered chunk of seal bone from Monterey Bay that resembled a shag carpet. When he looked at some of the worms under the microscope, he saw something strange: a trunk with a white mass at one end. When he dissected the worm, instead of finding ovaries, as he expected, he found testes. That white mass was sperm. He had found a species of Osedax in which the males aren’t dwarfs living inside the females’ ovaries, but are nearly as big as the ladies and chow down on bones, too. He uncovered more of the species when he examined bones he’d deployed off the coast of Oregon. “It was amazing,” he says. “But then there was the mystery of how they breed. How a male buried in bone comes into contact with a female.”

More time under the microscope revealed that males possess an extensible trunk that roams across the bone to find and inseminate females—kind of like a Go-Go Gadget penis. When Rouse officially described the species this past January, he named it Osedax priapus, after the Greek fertility god depicted with a permanent erection.

Such discoveries “make you wonder just how many more Osedax there are around the world,” says Rouse—and what other magnificently bizarre traits they might boast.

This article was originally published on onEarth, which is no longer in publication. onEarth was founded in 1979 as the Amicus Journal, an independent magazine of thought and opinion on the environment. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. This article is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the article was originally published by and link to the original; the article cannot be edited (beyond simple things such grammar); you can’t resell the article in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select articles individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our articles.

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