In an ocean popularity contest, jellyfish would rank near the bottom. They sting. Their increasing population blooms clog power plant intakes, kill farmed salmon and frighten swimmers. Experts warn of the jellification of the oceans.

True, jellyfish are biological marvels and efficient swimmers, and some achieve a kind of immortality. But they are by definition gelatinous — you might even say gooey — and scientists have spotted them blanketing the ocean floor after die-offs, suggesting that even for indiscriminating scavengers, jellies are not the carrion of choice.

However, the first experimental test involving a dead-jellyfish buffet tells a completely different story. Work done in Norway by Andrew Sweetman of the International Research Institute of Stavanger and his colleagues suggests that the impression left by previous ocean-floor observations may be the exception, not the rule.

They sank platforms loaded with jellyfish and other platforms loaded with mackerel more than 4,000 feet deep in the Sognefjord, Norway’s largest fjord. And what they found was that the seafloor cleanup crew — hagfish, crabs and other creatures — gobbled up the jellyfish just as fast as the mackerel, within a few hours.

The result was so surprising, Dr. Sweetman said, that the first time the researchers pulled up a bare platform after 18 hours at the bottom of the fjord, “we thought the jellyfish just washed off on the way down.”

Then they checked the video. “None of us could believe it,” he said. “It went against everything we thought.” He said, “You can actually see the hagfish burrowing in and eating the energy-rich gonads.”

Two kinds of jellyfish, helmet and lion’s mane, were used, and Atlantic mackerel. The researchers matched the amounts they put on the platforms and the size of the pieces. Scavengers arrived in minutes and usually finished the jellyfish in one to two hours and the mackerel in around eight hours.

This is exciting work,” said David Billett, a visiting research fellow at the National Oceanography Center in Southampton, England. In an email, Dr. Billett, who was not involved in the experiments, wrote, “It provides the first direct evidence that when jellyfish die, they don’t just fall to the bottom of the ocean as a pile of mush, but provide much-needed sustenance for a wide variety of deep-sea animals.”

The cases where jellyfish blanket the bottom, Dr. Billett said, may be rare events, perhaps in areas where jellyfish are not part of the regular diet of scavengers.

Lisa A. Levin, the director of the Center for Marine Biodiversity and Conservation at the Scripps Institution of Oceanography, who was not part of the research, said the experiments showed that jellyfish were not “a dead end in the food web.”

Instead, they are an important part of the system, which starts with plankton at the surface absorbing carbon dioxide. The plankton are eaten by other creatures, like jellyfish. “We may have been missing a big component of the downward transport of carbon,” Dr. Sweetman said.

What this means for the overall effect of jellyfish is not clear. They are still competing with other fish, their blooms can still cause problems for power plants, and for reasons that are not clear, they do sometimes end up in a mushy mess on the ocean floor.

But they are also far more important to the food web than first realized. And the credit for that discovery, Dr. Levin said, goes to Dr. Sweetman and colleagues, who managed to conduct a logistically difficult experiment.

Observations alone would miss the scavenging of jellyfish if they were consumed in a few hours. Information would come only from the chance discovery of big die-offs when they aren’t quickly consumed. So experiments are necessary, even if, as Dr. Levin said, “it’s not that easy to do experiments in the deep sea.”