No bone of contention for whale worms

“Worms devour whale bones!” Sounds like a National Inquirer headline but I rib you not; this story is legitimate and yet another example of truth trumping invention. Read on for the body of evidence. . .

When whales came to be, around 42 million years ago, they evolved with company in the form of specialized polychete worms that have only relatively recently been discovered. First identified in samples retrieved from a remotely operated vehicle (ROV) in the deep ocean in 1997, the novel worms were bestowed a new genus, Osedax (bone devouring) in 2004. Osedex and cohort worms of its ilk don’t prey on a whale during its life but intimately interact with it postmortem. Following an event scientists call a “whale fall,” the time when a whale dies and subsequently sinks to the seafloor, huge populations of various genera and species of these worms gather to feast and reproduce in ways foreign to us. 

Osedax species may look somewhat stylish but are all about function. The colorful, flowery plume is actually gills for breathing, the hollow pink stalk provides a retreat to retract into from danger, and the green “roots” dig into the bone, providing an anchor to the food source. Yet the worms have no teeth to gnaw on the bone and even if they did, they have no stomach to digest it. Instead, the bone devourers maintain an internal farm of symbiotic bacteria (where worm and bacteria benefit each other) within the rootlike structures to manage both jobs. As the bacteria break down the bone to meet their own nutritional needs, the waste products—fats and oils—are released to be absorbed by the worm hosts.

With the important processes of day-to-day living under control, reproductive matters can be considered. Scientists were originally mystified because all worms collected were females. Microscopic inspection then revealed that the females were not only full of eggs but also full of males. However, the minute-sized males don’t look like adult polychete worms. Instead, they remain suspended in a Peter Pan (larval) state with no chance of ever growing up. This is the euphemistic way to describe the male worms but to be blunt, the males are essentially containers of sperm. They exist solely to internally fertilize a female’s eggs.

This strategy likely evolved due to the precarious state of available whale skeletons on the ocean floor. Once a skeleton is consumed (2 to 4 years), the worms die off but not before releasing massive numbers of already-fertilized eggs. Worm spawn may be carried far and wide by ocean currents until a whale frame is detected, wherein a new--albeit ephemeral--worm community settles and flourishes to perpetuate the species.

Bone-devouring worm species like Osedax  have been hidden from human observation because they make their home in the deep ocean where little is known. Since their discovery, scientists have harnessed whale carcasses previously found dead and strategically dropped them into submarine canyons off the California coast in depths ranging from 400 feet to 3,000 feet. Information collected from these whale falls has reaped new worm species found at the various depths, with many new species discovered since then.

Greg Rouse, Curator of the Benthic Invertebrate Collection at Scripps Institution of Oceanography, is one of the researchers behind the discovery of some of these new species. In 2011, a 68-foot female fin whale killed by a boat’s propeller off San Diego was subsequently towed out to sea and sunk as a whale fall to be studied over the next several years. Dr. Rouse told me that he recently visited the site and will go again this March with an ROV operated by the Monterey Bay Aquarium and Research Institute (MBARI).

Rouse said, “The whale fall is spectacular and has provided some very interesting samples. There is a rich community of microbes and animals. We are comparing this site with whale falls in Monterey and also with organisms found at other unusual habitats such as methane seeps. There appear to be some new species at the whale fall, though many of the animals, such as Osedax, are ones we know.”

But the question remains: Are whale remains and the worms that remain worth studying for reasons beyond basic curiosity? Yes! These worms and their bacterial companions benefit the ocean ecosystem by recycling nutrients for many others, which ultimately benefits us. Well then worms, carry on, and bon(e) appetit.