‘Bone-eating’ zombie worms disappear from the sea floor, alerting scientists

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The long-term experiment was conducted by researchers from Ocean Networks Canada (ONC) and the University of Victoria (UVic), also in Canada. Humpback whale bones were deposited nearly a thousand meters deep in Barkley Canyon, a region naturally low in oxygen and located on the migratory routes of humpback and gray whales. In ten years, high-resolution underwater cameras have recorded no sign of colonization by Osedax, although we know that the worm quickly settles in these organic remains.

“This is a remarkable observation in such a long-term experiment,” said Fabio De Leo, senior scientist at ONC and associate professor in UVic’s biology department, who led the study. According to him, this absence could be linked to exceptionally low oxygen levels at the site.

Zombie worms play a fundamental role in the deep sea. They have no mouth, no anus, no digestive system. They survive by piercing bones with root-like structures, where they harbor microorganisms that can extract nutrients. Therefore, they are considered “ecosystem engineers” because they start the process of recycling nutrients and allow other species to colonize the remains of the whales.

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When a whale dies and sinks, its body creates a “whale crash,” an event that typically sustains rich biodiversity for years, functioning as a sort of oasis on the ocean floor. For De Leo, these falls are “almost like islands” and represent “a transit habitat for this species and many other species specializing in whale bones”.

The absence of Osedax suggests that the expansion of oxygen minimum zones (OMZs), associated with global warming, could interrupt this process. Without the worm that initiates bone decomposition, fewer organisms are able to access stored nutrients, compromising the entire ecological chain.

“Basically, we are talking about a potential loss of species,” warns De Leo. The adult worms live in the bones, while their larvae disperse hundreds of kilometers via ocean currents in search of new whale falls. If these habitats stop functioning, the connectivity between them breaks down, reducing diversity over time.

The impact is not limited to zombie worms. The study also identified signs of stress in another engineer of deep ecosystems: wood-eating mollusks of the genus Xylophaga. Although present in submerged wood samples from Barkley Canyon, they colonized the material at a much slower rate than in oxygen-rich areas, which may delay the decomposition of carbon and the formation of habitats for other species.

“It appears that the expansion of OMZs, a consequence of ocean warming, will be bad news for these incredible whale fall and timber ecosystems along the northeast Pacific margin,” said Craig Smith, professor emeritus at the University of Hawaii and co-author of the research.

Data was collected using ONC’s NEPTUNE underwater observatory, with the help of oceanographic sensors, fixed cameras and remotely operated vehicles. New results are expected in the coming months thanks to the monitoring of another whale crash at another location in the NEPTUNE network.