Underwater robots reveal the cannibalistic all-you-can-eat-buffet of the deep sea

The deep sea is filled with scaly and gelatinous creatures feasting on each other — and now we have an unprecedented view into this cannibalistic all-you-can-eat buffet.

Researchers at the Monterey Bay Aquarium Research Institute (MBARI) have analyzed 30 years’ worth of videos taken by underwater robots off the coast of California, to better understand who’s eating whom in the deep sea. Their findings, recently published in Proceedings of the Royal Society B, show that jellyfish are key predators, gobbling up a great variety of other species. One type of jelly for instance, in the genus Solmissus, was observed feasting on at least 22 different types of prey, from krill to worms to other jellyfish. That’s “pretty incredible for something that just looks like a clear dinner plate,” says study co-author Anela Choy, a postdoctoral fellow at MBARI.

Historically, scientists have been studying what deep-sea animals have for dinner by catching fish, opening them up, and literally counting what’s inside their guts. That has some obvious limitations: how easy can it be to identify a partially digested species? Gelatinous animals are in a particularly tough spot, because they decompose faster once they’re eaten and also easily dissolve once caught in nets. To solve these problems, scientists have been using remotely operated vehicles (ROVs).

These underwater robots can dive deeper than two miles, and take high-definition videos of whatever creatures are doing down there — including their meal times. Choy and her colleagues analyzed thousands of hours of footage of almost 800 instances of animals feeding on each other, from tentacled siphonophores grasping little fish to transparent jellyfish gobbling up red shrimp.

The scenes don’t get too gory, according to Choy. Having spent lots of hours slicing up fish to study their gut contents, “I’m sort of numb to the gore,” Choy tells The Verge. But they are sometimes shocking. Last July, Choy was on a ship off the shore of Monterey Bay, looking at the video footage transmitted by an ROV many feet below. A Gonatus squid was spotted sucking off the face of a “really huge dragonfish,” she says. “It took a little while to figure out what’s going on here, who’s eating whom, how is this going to end?” (The squid won.)

Overall, the videos revealed just how ravenous gelatinous creatures like comb jellies and medusae are, playing a critical role in the ocean food web. “Food webs are the backbone of our understanding of all life in the ocean,” Choy tells The Verge. And if we understand how animals are connected through feeding, then we can better understand how to conserve species and ecosystems, she says. So in a way, the tuna sandwich you eat is brought to you by the feeding frenzy happening in the dark recesses of the ocean.

For your enjoyment, here are some more postcards from that deep-ocean buffet. Bon appétit!