Jellies Down Deep

A Simple Plan for Supremacy

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Marine biologists have long struggled to understand how creatures living on the deep-sea bottom acquire enough organic material to support their growth. Larvaceans are an important part of the answer. Species in this class of chordates spin bubblelike webs of mucus around themselves to gather food. When the web becomes clogged, the animal discards it, swims off, and builds a new one. Meanwhile, the old web, thick with organic material, falls toward the seafloor and becomes a free lunch for another animal below. Thanks to larvaceans, the marine snowfall becomes a marine avalanche near the seafloor.

“In recent years we’ve learned that larvaceans account for a quarter to maybe a third of all the organic carbon that gets from the upper layers of the ocean—in Monterey Bay, at least—down to the deep-seafloor community,” Robison says. “They play a critical role in the transfer of energy from the sunlit layers to the deep seafloor.”

The immense number of jellies, and the many roles they play in food webs, could explain a larger mystery about Earth’s carbon cycle. To better understand the global climate and changes in the biosphere, scientists need an accurate measure of the total amount of carbon that is cycling between the planet’s living inhabitants, atmosphere, oceans, and solid earth. Consistently, however, they have faced a “budget gap” in their accounting. About 25 percent of the carbon that should be out there seems to be missing. Where is it?

Many marine biologists suspect that much of the missing carbon has been in front of their noses the whole time—in the transparent, gelatinous bodies of jellies. “Jellies are major players in the ocean’s carbon biomass,” Robison says. “They may be an overlooked part of the equation.”

Jellies may also be important indicators of the health of ocean ecosystems. Some biologists have speculated that jelly populations thrive as increasing numbers of shrimps, fishes, and squids are harvested from the oceans, leaving behind vast amounts of uneaten small prey. A rise in jellies may signal drastic changes underway elsewhere in the ocean. “There is evidence,” Robison says. “But while it’s compelling evidence, it’s not yet convincing evidence.”

What is clear to jelly scientists is how much of the deep sea remains unexplored, and how much there is still to learn about its gelatinous inhabitants. “You can’t really understand what’s going on in there until you know who the players are,” says MBARI’s George Matsumoto. “That’s where we are right now. We’re still trying to understand who all the different players are in the deep sea.”

Even in the deep sea, however, scientists are finding evidence of human impact. On one dive to the bottom of the ocean, MBARI scientists found numerous unusual jellyfish, as well as a beer can. “We know so little about these deep-sea environments and their inhabitants, yet we’re impacting them on a daily basis,” Raskoff says. “It makes us all a little bit nervous, because the environments are changing while we’re studying them.”