The deep ocean may be Earth’s largest ecosystem, but for obvious reasons it’s difficult to figure out what’s happening down there. A team of researchers is now shedding some light on the question of who eats whom in the deep, by examining decades of footage collected by robots off the central California coast. The surprising answer? Jellies eat everything.
“There is a misconception that jellies are merely a nuisance and serve no real purpose in marine ecosystems,” Steve Haddock, a marine biologist at the Monterey Bay Aquarium Research Institute and co-author on the new research, said in a statement. Now that we know that isn’t true, we need to start considering the fate of jellies in marine management strategies.
Until now, most investigations of who is eating whom in the deep ocean have relied on investigating the stomach contents of critters hauled up in nets. To gain additional insight, scientists have recently begun looking at the ratios of certain elemental isotopes within the tissues of deep sea predators, and comparing those with potential food sources.
Both of these methods require researchers to haul up a large number of animals, which presents a host of logistical challenges. Plus, this sampling system comes with biases. Soft bodied, gelatinous critters are often destroyed by nets, or decompose rapidly once reaching the surface.
To circumvent these issues, the study authors took advantage of hundreds of deep diving observations—totaling over 23,000 hours of footage—collected off the central California coast by Monterey Bay Aquarium Research Institute remotely-operated vehicles since the late 1980s. They uncovered almost 750 distinct video observations of animals devouring one another from 1991 to 2016, and analyzed all that data.
Isn’t science great?
“This direct approach has never been used systematically before,” MBARI ecologist and study co-author Bruce Robinson said in a statement. “Unlike other methods, it involves no guesswork and provides very precise information about who eats whom in the deep sea.”
The study’s results, published recently in the Proceedings of the Royal Society B, are transforming our understanding of the ecological importance of deep sea jellies, which were traditionally thought of as a dietary “dead end.” It turns out that in addition to previously recognized squids and large fishes, a broad diversity of jellies are important predators in this part of the world, particularly in mid-depth waters of about 200 to 600 meters.
Siphonophores, relatives of the Portuguese man-of-war that can create enormous “drift nets” and use them to snatch everything from krill to fish to other jellies, were among the most abundant predators at mid depths. The greatest diversity of prey, meanwhile was consumed by jellies of the order narcomedusae, like Solmissus, which was seen feeding on more than 20 different prey types from 100 all the way down to 1,700 meters depth.
“Who would have thought that a deep-sea jelly that looks like a big dinner plate would eat 22 different types of animals?” lead study author Anela Choy said.
“Interactions involving gelatinous predators and prey create most of the complexity that we see in our new deep-sea food web,” Haddock added.
The insight that the “jelly web” is far more complex than previously recognized has implications when considering humanity’s far-reaching impacts on the oceans. In recent years, there’s been loads of discussion about how jellyfish numbers may be increasing thanks to climate change and other factors, but claims that jellies are “taking over the oceans” are probably hugely inflated.
The new research suggests further study of how jelly populations might change is warranted, and for reasons that go beyond figuring out if future oceans are going to be full of vast, gelatinous blooms. If jellies exert an key control on other populations of deep sea critters, from fishes to cephalopods, any disturbance that affects them could have a cascade of ecological impacts.
More research is needed to suss it all out. “At the heart of it, if we don’t understand ecosystem structure we can’t conserve any single species or any part of the ocean,” Choy told Earther.
In the meanwhile, enjoy some GIFs of jellies and other deep sea predators devouring shit.