Zombie worms are missing and scientists are alarmed

In horror films, the most frightening threats are often the ones you cannot see. In the deep ocean, scientists are now facing a similar kind of unease, driven by the unexplained absence of a crucial species.

That species is the zombie worm, formally known as "the bone devourer" Osedax. Its disappearance may signal deeper trouble ahead, including species loss and weakening ecosystems linked to long-term climate change.

A Decade-Long Deep-Sea Experiment

Fabio De Leo, a senior staff scientist with Ocean Networks Canada (ONC) and an adjunct assistant professor in the University of Victoria's (UVic) Department of Biology, co-led a long-term experiment off the coast of British Columbia (BC). The study placed humpback whale bones on the deep ocean floor and monitored them for signs of life.

After years of observation, researchers found no trace of zombie worms, despite their well-known role in breaking down whale bones and supporting deep-sea food webs.

How Zombie Worms Feed Without a Digestive System

Osedax worms are unusual creatures. They lack a mouth, anus, and digestive tract, yet they survive by drilling root-like structures into bone. Inside those roots live microbes that extract nutrients, which then nourish the worms.

Because of this unique role, Osedax is considered an ecosystem engineer, helping recycle nutrients and create conditions that allow other species to move in.

Why the Absence Is So Concerning

Over 10 years of high-resolution underwater camera footage from ONC failed to capture any zombie worm colonization. In scientific terms, this kind of outcome is known as a negative result, and it can be just as meaningful as a positive finding.

"This was a remarkable observation in such a long-term experiment," De Leo says. He adds that the absence may be linked to unusually low oxygen levels at the study site.

Low Oxygen Zones and Whale Falls

The whale bones were placed in Barkley Canyon, nearly a thousand meters below the Pacific Ocean surface. This area lies within a naturally low-oxygen zone and along migration routes used by humpback and grey whales.

When whales die from natural causes or human-related threats such as ship strikes or fishing net entanglements, their bodies sink to the seafloor. These events create "whale falls," which normally provide a sudden surge of food that supports rich biodiversity. The lack of zombie worms at Barkley Canyon suggests that expanding oxygen minimum zones (OMZs) in the northeast Pacific and beyond may be disrupting these ecosystems.

Early data from ongoing whale fall research near another ONC NEPTUNE site points to similar concerns elsewhere.

Why Bone Devourers Matter

If the "bone devourer" is missing, the chain reaction can affect many other species. Without Osedax to break down bones and kick-start the ecological succession process, fewer organisms may be able to access nutrients stored in whale remains.

Whale falls are "almost like islands," De Leo explains, calling them "a stepping-stone habitat for this and many other whale bone specialist species."

The Risk of Species Loss

"Basically, we're talking about potential species loss," De Leo says. Adult Osedax typically live on whale bones, while their larvae travel long distances through ocean currents to colonize new whale falls, sometimes hundreds of kilometers away.

If those habitats disappear or stop functioning properly, connectivity between whale fall sites breaks down. Over time, this could lead to declining diversity of Osedax species across entire regions.

Other Deep-Sea Engineers Also Affected

The research team also found signs that another ecosystem engineer may be under stress. Wood-boring Xylophaga bivalves were present on submerged wood samples at Barkley Canyon, but their colonization rates were far lower than in oxygen-rich waters.

Slower colonization could delay carbon decomposition and reduce habitat formation for the many species that typically live inside Xylophaga burrows.

"It looks like the OMZ expansion, which is a consequence of ocean warming, will be bad news for these amazing whale-fall and wood-fall ecosystems along the northeast Pacific Margin," said Craig Smith, professor emeritus from University of Hawaii, who co-led the experiment.

How Scientists Collected the Data

De Leo and Smith relied on ONC's NEPTUNE observatory Barkley Canyon Mid-East video camera platform, along with oceanographic sensors and high-definition video collected by remotely operated vehicles.

Additional findings are expected in the coming months from a whale fall currently being monitored at NEPTUNE's Clayoquot Slope site.

The research was supported by the Canada Foundation for Innovation Major Science Initiative Fund and partly by a US National Science Foundation grant. It also aligns with United Nations Sustainable Development Goal 14, life below water.