Underwater Robot Tracks Elusive Jellyfish

Bijal P. Trivedi
National Geographic Today
January 17, 2003
The creatures that slip through the nets fascinate Bruce Robison.

Robison, a deep-sea ecologist at the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., used to work with what he calls "respectable animals"—those large enough for research vessels' nets to catch.

"The nets would haul up fish and squid, which were all covered in a clear goo that we'd scrape off the top and throw over the side," Robison says.

Studying that transparent, amorphous "goo"—a puree of jellyfish and other gelatinous sea dwellers—provides clues to the nature of the undersea food chain. And the ubiquity of these creatures throughout the world's oceans makes them a silent sentinel of environmental change.

For example, some researchers believe that higher water temperatures from global warming may have boosted the number of comb jellies in Rhode Island's Narragansett Bay, says Larry Madin, a marine biologist at the Woods Hole Oceanographic Institution in Massachusetts.

And a tenfold increase in jellyfish numbers in the Bering Sea, also perhaps climate-related, has led observers to dub one area of the Alaskan peninsula the "Slime Bank."

"I was amazed by how many jellies there are," Robison says. "Just using nets, we've missed about one third of the animals in the oceans."

Chasing Jellies

Robison and his collaborator Jason Rife, a doctoral candidate in a robotics laboratory at Stanford University in California, are venturing out on the high seas with a camera-equipped underwater robot that tracks jelly-like creatures in their own domain.

Rife designed the software and the camera system for the remotely operated vehicle, or ROV, dubbed the Ventana. A cable tethers the ROV to the research ship.

On board the ship, about seven miles off Monterey Bay, one of the researchers in a control booth directs Ventana's movements between 900 and 3,000 feet below the surface until the camera finds a jelly of interest.

Rife's computer program creates a profile of the creature and begins to autopilot the craft, all the while keeping the animal in view as it drifts through a chilly, dark world.

"When this thing is working properly, we are bored stiff and just sit around talking," says Rife. "It's a lot like playing a video game—just keeping the target in the center of the screen."

During the past year, Rife has chased jellyfish on seven Ventana missions. The Ventana's tracking record to date is 89 minutes on one jelly.

The Ventana opens a window on a world of exotic creatures. Gelatinous animals include more than just the medusa-like jellyfish that wash up on the beach—like comb jellies, which have a different architecture, and no stingers.

Other more sophisticated jelly creatures include some mollusks and snails, and tunicates—sea squirts, salps and larvaceans.

All these creatures—about 95 percent water—play a vital role in the ocean food chain, "where everyone's just looking for a good meal," Rife says.

Mucus Houses

Rife has tracked several larvaceans—transparent, tadpole-like animals about the size of a BB that construct so-called "filtering houses" to catch food.

These houses are three-dimensional mucus-nets or webs. The coarse outer web catches unwieldy particles. The fine inner filter of the house, which looks like a pair of clenched fists, catches microscopic food particles and sends them directly through a pipe to the animal's mouth.

The entire house structure, with tiny particles stuck in its sticky thread, glitters like a diamond encrusted fishing net. In deep water these houses can stretch up to six feet wide.

When the house becomes clogged with excessive debris the larvacean abandons it and builds another. The houses eventually collapse under their own weight and sink, carrying the nutrient-loaded scaffold to the ocean floor—providing food for deep-sea life.

"We always thought, and taught, that nutrients reached the ocean floor as a fine rain of sediments," says Robison. "For decades we knew deep sea ocean floor was using more food than could be accounted for, and now, here we have an unaccounted-for transport mechanism for getting nutrients to the ocean floor."

The jellies reveal a remarkable adaptability and even a sense of community.

"Simple as they are, these life forms are capable more sophisticated behavior than we thought," Madin says.

With just a basic network of nerves, the jellies can smell and taste food, detect light and possibly sense their topography. Many perform dramatic vertical as well as horizontal migrations and form aggregations of millions of creatures at particular times of the year.

"Jellyfish have been around for 500 to 600 million years—they are a very early, very successful form of life," Madin says. "They keep it simple."

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