The giant deep-sea octopus (Haliphron atlanticus) is an enigmatic critter. Few marine biologists have ever spotted the cephalopod—scientists at the Monterey Bay Aquarium Research Institute, for instance, have only recorded three sightings in the last 27 years. So researchers were surprised when they recently caught a glimpse of one of these creatures. But what stunned them even more was what it was eating: a large, squishy jellyfish.
As George Dvorsky explains for Gizmodo, some scientists have argued that jellyfish are low in nutritional value, so do not play a significant role in the marine food chain. But the recent study of the Haliphron’s dietary preferences, published this week in Scientific Reports, suggests that the importance of gelatinous sea creatures as prey has been underestimated.
Most of what scientists know about the Haliphron—also called the “seven-armed octopus” because males keep their eighth tentacle tucked in a sack under the eye—comes from studies done on specimens that have been scooped up from the ocean by fishing nets. Though the males are relatively small, growing to about 12 inches long, the females are huge, stretching up to 13 feet in length and weighing up to 165 pounds. Prior to the new study, however, researchers weren’t sure what the octopus ate to maintain its impressive size.
Hoping to observe the Haliphron in its natural habitat, marine biologists from the GEOMAR Helmholtz Centre for Ocean Research in Germany and the Monterey Bay Aquarium Research Institute set out on an expedition off the coast of California in 2013, Jane J. Lee reports for Nature. They used a “deep-diving robot” to search for the elusive octopus, and found one clutching a large, egg-yolk jelly.
In a video by the Monterey Bay Aquarium Research Institute, marine biologist Steven Haddock explains that the Haliphron had eaten through most of the tissue hanging down from the bell of the jellyfish. The octopus had pierced the bell with its beak, leaving the ring of the tentacles intact.
Incredibly, the Haliphron continued to hold onto its prey even after it had finished chowing down. “It looked as though Haliphron had not only made a meal of the jelly, but was hanging onto it, perhaps for a defense, or for help in catching more prey,” Haddock says.
To confirm that this wasn’t a one-off occurrence, researchers checked archived footage of the Haliphron and noticed that at least one other creature appeared to be holding a gelatinous creature. Gizmodo’s Dvorsky writes that the team also analyzed the stomach contents of five Haliphrons that had been caught in fishing nets. All of their stomachs contained traces of gelatinous zooplankton, and three had bellies full of jellyfish.
These findings add to a growing body of research that suggests jellies play a more important role in the marine food chain than previously believed. Recent studies have shown that gelatinous animals feature prominently in the diets of spearfish and two different types of tuna. Penguins and lobsters have been known to munch on jellies too. And according to Lee, other species of octopus use jellies in complex ways. Some cephalopods have been observed wielding the tentacles of jellies, possibly to help catch more prey—just like the Haliphron seemed to be doing when it held onto the remains of its meal.
The authors of the study note that the Haliphron can afford to feast on low-calorie jellies because it has “a very low mass-specific metabolic rates” and doesn’t require much energy to maintain its metabolism. Or as Haddock says in the video, the octopus displays an “interesting adaptation to life in the open ocean: live slow, grow big.”