In early 2002, researchers at the Monterey Bay Aquarium Institute (MBARI) were using the remotely operated vehicle (ROV) Tiburon to investigate deep-sea clams off Monterey Canyon. While there, they came across the skeleton of a whale that had apparently been picked clean by what seemed to be a “carpet” of tiny, worm-like creatures. “They were growing like crazy,” said MBARI biologist Robert Vrijenhoek in a news release about the discovery, “carpeting the remaining whale bones. The worms had short trunks topped by red plumes, and were about an inch or two in height.” When researchers had a chance to examine the creatures more closely, some weren’t convinced they were even worms. All did agree they were very strange, but very few probably could have imagined just how strange they’d turn out to be.
DNA analysis confirmed these creatures were indeed annelids, related to other species of tubeworms that live around hydrothermal vents. Like the vent worms, the whale worms had bright red plumes that acted as gills, collecting oxygen from seawater. Unlike the vent worms, however, these worms had green, root-like structures that penetrated the whale bones and branched out in the marrow cavity. These roots, in fact, turned out to be the most important part of the worm’s body, containing specialized bacteria allowing for the breakdown of the oils and proteins in the bones.
But things began to get strange when researchers couldn’t seem to find any males among the specimens brought up to the surface. Things went from strange to utterly bizarre when they discovered that males did exist, but that, in this species of worms, the males never passed the larval stage. They instead lived in groups of 30 to 100 inside a female’s body. In short, males don’t feed like the females do but instead live off the yolk of the egg that produced them, all the while producing sperm for the further propagation of the species. Why such an odd method for keeping the species going? Dr. Vrijenhoek suggests the worms are like the “ecological equivalent of dandelions—a weedy species that grows rapidly, makes lots of eggs, and disperses far and wide.” The strategy makes sense when you consider what depending upon dead whales as a source of food would entail. Once the worms had picked the whale clean, they’d run out food. Releasing as many tiny larvae as they could and having the ocean current carry them away would increase the chances of them landing on another whale carcass.
Over the next three years, MBARI scientists sank whale carcasses from depths of 400 to 1,800 meters and discovered as many as 12 species of these strange, bone-eating worms living just in Monterey Bay alone. Later, additional species were found off the coasts of Sweden and Japan. The scientists gave the worms the name Osedax, which is Latin for “bone-eating.” They found that different species of the worms appeared at various depths and attacked the whale carcass at different stages of decomposition.
…the worms crawl in, the worms crawl out…
In less than a decade, this previously unknown species of worm has gone from anonymity to something of a cultural phenomenon, inspiring things such as children’s hand puppets and the name of a rock band. Regardless of their roles, it seemed that these worms had one thing in common: they fed on mammals. Such a strict diet, however, would have implications for when the Osedax could have developed. If only able to feast on mammalian bones, the Osedax could not have have evolved during the Cretaceous period, well before the dawn of marine mammals, as many seemed to believe. To solve the puzzle, researchers from the Scripps Institution of Oceanography at the University of California-San Diego decided to set some bait for the worms. Again using ROVs, the scientists sunk tuna and Wahoo bones, as well as shark cartilage, to a depth of 1,000 meters off Monterey Canyon. Collecting the bones five months later, they found three distinct species of Osedax growing on them. (The shark cartilage apparently fell prey to other organisms.) This experiment proved that the Osedax weren’t whale bone specialists but bone-eating generalists.
The Scripps and MBARI researchers plan to continue their studies of the nutritional limits of the Osedax, in particular concentrating on how they might be able to use shark cartilage. The researchers are also interested in coming to a better understanding of exactly how the Osedax feed off the bone. If past findings are any indication of what to expect, undoubtedly they will find many new species of these strange ocean-dwelling worms.
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