From Goo to Zoo
When Bruce Robison was just starting out in marine biology, the study of deep-sea life usually involved dragging a net behind a ship. This method was efficient but selective, he recalls. Trawl samples gave scientists a skewed picture of what populates the oceanic water column: large numbers of fishes, crustaceans, and squidsthe hard-bodied animals the nets could actually snareplus “a handful of goo” that was tossed overboard.
But the goo is a crucial piece of the oceanic puzzle, Robison realizes now. A deep-sea ecologist at the Monterey Bay Aquarium Research Institute, Robison has pioneered the use of submersible robots to study jellyfish and other gelatinous invertebrates in their native deep-sea environment. Once you enter their home, these organisms, known collectively as jellies, are hard to miss. As it turns out, they are a dominant form of life in the ocean, far more abundant than previously realized. Robison estimates that as much as 40 percent of the biomass in the open ocean is bound up in the bodies of gelatinous invertebrates.
“Jellies are a completely surprising component of the deep-sea food web,” Robison says. “Our present understanding of where jellies fit into the way the world works is far from complete. But it’s very clear they are a significant part of deep-ocean communities.”
“Jelly” is a generic term that marine scientists use to describe transparent, gelatinous invertebrates that float freely in the ocean. Jellies encompass more than just jellyfish, which themselves include about 200 species in the class Scyphozoa (phylum Cnidaria). Jellies come in all sizes, from the microscopic to dozens of feet long, and in uncounted forms. Their membership consists of species from widely divergent taxonomic groups, including true jellyfish from the phylum Cnidaria, comb jellies from the phylum Ctenophora, sea snails and sea slugs from the phylum Mollusca (most mollusks, such as the familiar, hard-bodied clams and mussels, are not jellies), and a small group from the phylum Chordata (which mostly includes non-gelatinous animals such as birds, reptiles, and people). Jellies are defined not by a single, shared evolutionary ancestry, but rather by the outward fact that they all have gelatinous bodies.
Through the use of remotely operated submersible vehicles, or ROVs, scientists at MBARI have gained unprecedented access to the jellies’ realm. A scientific ROV is essentially a swimming robot outfitted with research equipment such as sampling containers, headlights, and high-resolution video cameras. While the vehicle dives deep into the cold undersea darkness, scientists sit comfortably aboard a ship on the sea surface, controlling the ROV movements remotely and watching its video feed on a bank of screens. Manned submersibles are also used in studying jellies, but an ROV, freed from its human occupant, can run longer without resurfacing and makes an excellent camera platform.
Monterey Bay is an ideal harbor from which to launch jelly expeditions. Its waters are biologically rich, and not far offshore the seafloor plunges into Monterey Canyon which, at 3,800 meters (13,000 feet) deep, is one of the deepest submarine canyons along the continental United States. In just a few hours’ travel time, an ROV can be positioned for a plunge into the deep sea. Such speed cuts the expense of jelly research, so more of it can be done, and any live jellies captured by the ROV can quickly be returned to shore for further study.
MBARI scientists have put ROVs to work performing various tasks. One simply involves gathering data about jellies: how many of which kind are where, what they do, and when they do it. The ROVs make underwater runs of a certain length at different depths, filming all the while. Later, scientists watch the video and count all the jellies they can. The work is tedious but enlightening. For the first time, scientists are estimating how many jellies are actually down there. And they can monitor how jelly populations change over timewith the seasons or in relation to long-term climate cycles like the El Niño southern oscillation.
Submersible vehicles also offer a unique window on jelly behavior and ecology. “One of the advantages of working on jellies is that they’re blind and deaf,” Robison says. “They don't seem to mind at all when we fly up to them and zoom in with our lights and cameras. We can make good observations of the interactions of jellies with one another, their prey, and their predators, without disturbing them.” And the jellies themselves, being transparent, offer an additional window onto their lives. “Who eats whomthat’s easy to see with a transparent animal,” Robison says. “You don’t have to cut them open to find out what was for lunch.”
Finally, submersible vehicles have provided MBARI scientists with the ability to capture unusual jellies and transfer them live to the lab. It’s a delicate process involving what California State University, Monterey Bay researcher Kevin Raskoff calls “the slurp gun,” a suction device that gently draws a jelly and a small volume of its watery habitat into a container. When the submersible returns to the surface ship, the jelly is quickly transferred to a dark, temperature-controlled environment.
“These animals are in a very stable, low-temperature environment for their entire lives, and many of them live in almost complete blackness,” Raskoff says. “Even a slight temperature change or a little bit of sunlight can be damaging.”
What the ROV doesn’t catch, it can capture on video. These videosthousands of hours worthhave helped MBARI scientists identify several new jelly species. In May 2003, Raskoff and his colleague George Matsumoto announced the discovery of Tiburonia granrojo, a meter-wide, tentacleless jelly that they’ve nicknamed “Big Red.” The animal, which lives 650 to 1,500 meters (about 2,000 to 4,800 feet) underwater, was captured on video as early as 1993, but Raskoff and Matsumoto needed several years to confirm that it wasn’t just bizarre-looking but was in fact a distinct, undescribed species. “The majority of the jellies we’re now finding never saw the light of day,” Matsumoto says. “They’re down deep, out of the reach of the nets. And even if they could be reached by the nets, they would be crushed by the time they finally got back up to the surface.”
The exploration is only beginning. The deep sea is an enormous place. The ocean surface itself occupies 71 percent of Earth’s surface area, and below every square foot of ocean surface are, in many cases, miles of water teeming with lifemuch of it gooey and translucent. As available space goes, the deep sea is by far the largest ecosystem on Earth. And Monterey Bay, one of the best-explored deep-sea regions, represents only the smallest slice of the total. “We’ve still only explored a tiny fraction of the deep ocean,” Robison says, “so we know relatively little about all the different kinds of jellies that are out there.”
There’s a huge amount to be learned: not only which (and how many) jellies exist, but just as important, what they’re all doing down there. “ Jellies have had a bad reputation for a long time, because most people only encounter them in negative situations,” Robison says. “They’re far more important and significant and interesting than that.”
A typical collection of drawings from the early days of jelly science.
More About This Resource...
Our innovative Science Bulletins are an online and exhibition program that offers the public a window into the excitement of scientific discovery. This essay was published in June 2004 as part of the Jellies Down Deep Bio Feature.
- It opens by explaining the limitations of trawl samples, which give scientists a skewed picture of what populates the oceanic water column.
- It then details how a deep-sea ecologist at the Monterey Bay Aquarium Research Institute is using submersible robots to study jellyfish and other gelatinous invertebrates in their native deep-sea environment.
- The essay concludes by explaining that the deep sea is by far the largest ecosystem on Earth, and that Monterey Bay, one of the best-explored deep-sea regions, represents only the smallest slice of the total.
Supplement a study of biology with a classroom activity drawn from this Science Bulletin essay.
- Have students read the essay (either online or a printed copy).
- Working individually or in small groups, have them research the meter-wide tentacleless jelly "Big Red" (Tiburonia granrojo) Raskoff and Matsumoto discovered and report what they learned about this new jelly species to the class.