It’s almost Halloween, which means bones, skulls and skeletons are casually strewn across people’s lawns. But for scientists working in the Monterey Bay National Marine Sanctuary, mid-October also means it’s time for the exploration vessel Nautilus' last research dive of the season.
However, about 20 hours into the dive the team stumbled across a spooky surprise of their own: an approximately five-meter-long, complete baleen whale skeleton resting belly-up on the seafloor.
The team was scouring an underwater mountain off the coast of California, the Davidson Seamount, about 3,200 meters below the surface using their Hercules remotely-operated vehicle (ROV) at the time, but they hadn’t set out to find the skeleton. (Viewers can get a round-the-clock glimpse at the expedition via the Nautilus Live video feed, where you can listen to scientists narrate their work as it unfolds.) When the researchers spotted the whale carcass, they turned the ship around for a closer look. Hercules spent the next few hours collecting sediment cores around the skeleton, imaging the bones, and plucking plant and animal samples from the carcass to study in the lab after the team surfaces.
When a whale dies and sinks to the bottom of the ocean, it’s aptly called a “whale fall.” The whale in question landed on its back where it settled in for decay. Researchers estimate that the whale likely died about four months ago because partial organs remained, blubber was present, and baleen was still attached to the whale's jaw, which is how they were able to identify it as a baleen whale. (At the time of publication, the team hadn’t yet identified what specific species of baleen whale it was. To be sure, scientists will need to wait for environmental DNA analysis.)
More than a dozen octopuses—including one that hitched a ride on Hercules for a bit—were clinging to the whale’s spine and rib bones. It was especially odd to see the octopuses clutching the skeleton, as the animals generally hunt live prey, but octopuses have been seen crowding around whale falls before. According to researchers on shore, the octopuses were likely chowing down on living crustaceans, not blubber remaining on the bones.
Announcement: Citizen science isn't just for humans anymore. This octopus was just hanging out on @EVNautilus's ROV Hercules in @MBNMS!— Sanctuaries (NOAA) (@sanctuaries) October 16, 2019
Watch live: https://t.co/j6ZC2wpapT
Learn more: https://t.co/OFhwzKxGJp#SanctuariesLive pic.twitter.com/iAACjuA4v1
Large scavenger fish like eelpouts munched on blubber while red bone-eating Osedax worms gnawed fat from the bones. Also present were crabs, grenadier fish, bristle worms, sea pigs and a big squat lobster—possibly fattened up from a feast at the skeleton, one scientist joked.
Whale falls are an exciting smorgasbord for ocean communities—and for ecological research. A dead whale can support deep-sea communities for years to decades, according to NOAA. In the first few months, scavengers pick the bones clean. Later, invertebrates use the hard surface of the bones as a new home. As organic compounds in the bones decay, microbes can feed off the energy released from chemical reactions for years to come. As long as the food lasts, an ecosystem will thrive.
One scientist pointed out the irony of finding a whale fall during the current season ... fall, and a commenter pointed out that the scientists—who were overjoyed by the find—must have been having a “whale” of a time. The team is well aware of the upcoming holiday as well.
"What an amazing find in preparation for Halloween," one scientist remarked.