Researchers who filmed a whale decomposing on the seafloor across more than a decade, now know how long it takes the bacteria that break down bones to do their job. Their results are presented in Frontiers in Marine Science.
In 2009, researchers spotted the body of a large whale – maybe a blue, maybe a fin – resting on the seafloor, almost a mile deep, off Vancouver Island, British Columbia. With most of soft tissue already missing, they realised the carcass presented an opportunity.
Whale decomposition occurs in stages. First, mobile scavengers feed on the soft tissue. Second, small opportunists colonise the bones and surrounding sediment. After that, bacteria break down lipids inside the bones, releasing sulphur-based chemicals that are consumed by other specialists.
Researchers have debated how long this third ‘sulphophilic’ (sulphur-loving) stage takes. Now they had a chance to find out.
“What was so special,” says Fabio De Leo from the University of Victoria, “is that unlike any previous whale fall studies, we were able to return to the same location and survey the skeleton with a cm-scale precision photogrammetry technique.”
Remote-operated vehicles (ROV) revisited the same site across 15 years, recording high definition video and other measurements.
Subtle, significant changes were noted. Between 2012 and 2023, the mandible and 22 vertebrae shrank in length by 1.4 and 7.8 per cent respectively. At the same time, a fuzzy white microbial mat of sulphophilic bacteria grew over the bones.
So-called ‘zombie worms’ - which bore into and feed on bone - were present at the start of the survey, but absent by its end, when many sulphophilic species were spotted, including vestimentiferan tube worms and vesicomyid clams.
Collectively, this suggests that the sulphophilic stage has been ongoing for at least 21 years and may last for another decade. This is longer than some previous studies had predicted.
According to De Leo, this means that “animals that are whale fall specialists will always find a new home when their larvae drift away, as other whale carcasses will be persisting on the seafloor in the same sulphophilic stage.”
But it’s a double-edged sword. Climate change is thought to be causing the expansion of oxygen-poor patches of ocean, known as oxygen minimum zones (OMZs). If a carcass winds up in an OMZ, zombie worms may be unable to colonise it. “This in turn will impact the entire bone erosion process, says De Leo. “The overall effect would be the decrease of total species diversity at the whale fall.”
Image and video credit: Ocean Networks Canada (ONC) and Ocean Exploration Trust (OET) | Read more about the study, published in Frontiers in Marine Science.
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