Jellies Down Deep

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 squids–the hard-bodied animals the nets could actually snare–plus “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 time with 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 whom that’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 videos thousands of hours worth have 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 life much 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.”

Only in recent years have marine biologists come to grasp the astonishing abundance of gelatinous animals in the world’s waters. By some estimates, transparent jellies make up as much as 40 percent of the biomass in the open ocean. Now, with an improved ability to detect and study these creatures, scientists are slowly coming to a more complete understanding of how ocean food webs work.

“Jellies were always relegated to an interesting but fringe category of strange, snotty animals in the water,” says Kevin Raskoff, a jelly scientist at the Monterey Bay Aquarium Research Institute. “But once we saw how prevalent they are and the diverse habitats they’re found in, it caused us to rethink their role in ecosystems as a whole.”

Jellies share a remarkably basic construction. The “jelly” in jellies is little more than a mixture of saltwater and some carbon-containing sugars. True jellyfish (phylum Cnidaria, class Scyphozoa) are made of two transparent layers, an outer one for protection, and an inner one that handles digestion. In between, a small amount of fibrous jelly called mesoglea serves as the scaffolding for everything else what little there is. Ctenophores, or comb jellies, have a similar construction. As a general group, jellies possess a large percentage of watery, transparent tissue.

Being gelatinous has its disadvantages. Jellies are slow and vulnerable to some predators like sea turtles. But having a gelatinous body also provides many advantages. Because jellies are made mostly of water, they are neutrally buoyant, so they waste no energy maintaining their position in the water. Their body material is “cheap to build,” says MBARI scientist Bruce Robison, so a jelly can easily repair most damage it sustains. And jellies can respond quickly to changes in their habitat. When food becomes plentiful, they can grow and reproduce rapidly. When food is scarce, a jelly can actually shrink, or “de-grow.”

“Jellies are perfectly adapted to a three-dimensional watery habitat,” Robison says. “The fact that we see so many different kinds of them reflects the fact that they have a fundamentally successful body plan and way of making a living.” 

With a better estimate of how many and what kinds of gelatinous animals exist, scientists are filling gaps in their understanding of oceanic food webs. Using the same basic material, jellies have assumed diverse roles. Some graze on krill and plankton, and will even actively migrate up to surface waters at night to eat their fill. Others snack on “marine snow,” an omnipresent mist of food particles that drifts down from the sea surface to the seabed and includes tiny plankton living and dead, fish feces, and exoskeletons shed by their former occupants. Some jellies prey only on fish, others only on crustaceans. Still others have specialized features with which to prey on their gelatinous cousins. Some jellies of the genus Beroe, for example, are little more than a mouthlike sac that ingests other jellies.

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.”

The deep sea is ruled by darkness. Sunlight does not penetrate much beyond 60 meters (about 200 feet) below the ocean’s surface. To see the animal life, gelatinous or otherwise, that thrives at greater depths, a submersible vehicle like the ones used by scientists in Monterey Bay comes equipped with powerful lights. To truly understand the life down there, however, those lights must be turned off. That’s when the native lights become visible--the ghostly blue flickers of bioluminescence produced by virtually every organism of the deep.

“There’s a whole netherworld of the deep sea that we don’t see when we have our lights on,” says Kevin Raskoff, a scientist at California State University, Monterey Bay. “And that’s the natural light of the deep sea: bioluminescence.”            

“It’s such a bizarre and exciting phenomenon to see,” agrees Steven Haddock of the Monterey Bay Aquarium Research Institute. “The first time you see one of these animals just glow, it’s pretty amazing.”           

Bioluminescence is light produced by a chemical process within a living organism. The glow occurs when a substance called luciferin reacts with oxygen. This releases energy, and light is emitted. An enzyme called luciferase facilitates the reaction. Sometimes luciferin and luciferase are bound together with oxygen into a single molecule, or photoprotein. When an ion such as calcium is present, an ensuing reaction emits light. To glow on a regular basis, an organism must continually bring fresh luciferin into its system. Some acquire it through their diet; others produce their own.

Bioluminescence is relatively rare on land. It is most commonly seen among certain insect species like fireflies and glowworms (a form of insect larvae); some mushrooms and fungi also glow in the dark. In the deep sea, however, bioluminescence is found in virtually every type of animal: squids, octopuses, fishes, shrimps, single-celled organisms, and jellies of all kinds. Two thousand years ago, the Roman scholar Pliny the Elder noted that if he rubbed the slime of Pulmo marinus, a jellyfish from the Bay of Naples, on his walking stick, it “will light the way like a torch.” Raskoff estimates that 90 percent of all the animals in the deep sea are in fact bioluminescent. “In the deep sea, it’s the norm. You’re odd man out if you don’t bioluminesce.”      

Underwater, bioluminescence finds all manner of purpose. Some animals use it to attract mates. A male sea-firefly (Vargula hilgendorfii) will squirt out a bright dot of light, zip upward, and then squirt another and another, essentially drawing an arrow that points out his whereabouts. Other creatures use bioluminescence to detect or lure prey. The viperfish ( Chauliodus sloani) dangles a luminescent lure in front of its mouth and then snaps up any creature that dares to investigate. 

Other organisms use their bioluminescence to fend off or dupe predators. The deep-sea shrimp (Acanthephyra purpurea) vomit bioluminescent goop into the face of threatening diners, presumably either as a scare tactic or to create a distraction while the shrimp escapes. Other organisms seem to employ their bioluminescence as a kind of defensive burglar alarm: they light up to attract a second predator that will eat the first one (or to make the first predator think that a second one is coming, and so prompt it to leave).

For still other animals, bioluminescence provides camouflage. Certain species of squid bioluminesce only on the underside of their bodies, so they match the background light shining down from above; this hides their silhouettes from any predators or prey below. Many shrimp and fish emit a constant, dim glow to match the ambient light around them. In short, there is no single answer for why organisms bioluminesce, and no shortage of scientific debate around the subject. “We have little tantalizing indications of how it may benefit them,” Haddock says. “But we don’t have really a good explanation that applies across the board.” 

A larger mystery is how bioluminescence evolved in the first place. In recent lab experiments, Haddock has found that many jellyfish don’t produce their own luciferin; rather, they acquire it from their diet, which consists of small, bioluminescent crustaceans. This suggests to Haddock that, although jellyfish first emerged hundreds of millions of years ago, they gained their bioluminescent abilities much later, after consuming luciferin proved to be advantageous. 

Scientists themselves have had to adapt in order to study bioluminescence. The collection of live jelly specimens, made possible by the development of submersible vehicles, has made it easier for researchers like Haddock to study bioluminescence up close in the lab. Edith Widder, a marine scientist at the Harbor Branch Oceanographic Institution in Florida, is developing “Eye in the Sea,” a supersensitive camera that will sit on the seafloor and watch bioluminescent organisms light up in their natural environment.

And much like jellies, many scientists have even incorporated bioluminescence into their own work lives, often unaware of its original origin.  Photoproteins, first isolated from jellyfish several decades ago, are now an integral part of laboratory biology and help researchers do things like mark and identify crucial gene sequences in medical studies.

“Jellies are important for humans,” Haddock says. “They have provided us with a lot of the tools that we use now in molecular biology. You can have a biomedical researcher who is using a photoprotein that came from a jellyfish. He has no idea where it came from. He just knows that it’s one of the most useful tools that he has in his lab.” 

Therein lies the importance of doing of basic research in the natural world, he adds. One never knows where a discovery might lead, or when the study of a weird, or cool, or seemingly unimportant phenomenon might shed light on everyday human matters. “You can be asking a question just based on your curiosity,” says Haddock, “trying to figure out how these organisms make this light, how did it come about, without thinking all the way ahead to all the ways that it might be used to cure cancer someday. Yet the tools that come out of this phenomenon can then be applied to a lot of things that really impact everyone.”

Almost from the moment George Matsumoto of the Monterey Bay Aquarium Research Institute first saw “Big Red,” he knew he was looking at a new species of jellyfish. It looked just plain bizarre: bulbous, dusky red, and huge, nearly one meter (about three feet) in diameter, with several fleshy arms instead of tentacles, like a balloon with greedy fingers. When Matsumoto and his coauthors, Kevin Raskoff of California State University and Dhugal Lindsay of the Japan Marine Science and Technology Center, described it in a scientific paper in 2003, they gave it a more official name: Tiburonia granrojo.

“Because we’ve spent so much time in the field and we’ve seen so many pictures, whenever we see something that doesn’t match up we get this feeling that it’s a new species,” Matsumoto says, “which of course generates a lot of excitement and enthusiasm.” 

These are busy times for jelly discoverers. The use of submersible vehicles has enabled scientists to explore the world of jellies in depth; new creatures are constantly appearing. In February 2004, Raskoff and Matsumoto announced the discovery of yet another deep-sea jelly, Stellamedusa  ventana, a tentacleless organism they’ve affectionately named “Bumpy” for the many warty lumps on its softball-size body. 

The best-known groups of jellies are the jellyfish and comb jellies. Jellyfish belong to the class Scyphozoa within the larger phylum Cnidaria. All cnidarians possess stinging cells called nematocysts. The phylum Cnidaria also include the classes Hydrozoa, Anthozoa (corals and sea anemones), and Cubozoa (sea wasps and box jellies). Comb jellies belong to an entirely separate phylum, Ctenophora. The ctenophores gather food and ensnare prey with sticky cells rather than stinging cells. Unlike cnidarians, which propel themselves with rhythmic contractions of their bells, comb jellies paddle through the water with tiny oarlike cilia on the outsides of their bodies. Though many jellyfish and comb jellies look outwardly similar, the two groups are evolutionarily distinct.  Only recently have scientists successfully described Cnidaria and Ctenophora as distinct phyla. Due to similarities in appearance, the two together had previously been known as coelenterates. 

Classifying a new jelly species is a difficult process. “Every time I do it, it’s a lot of work, but it’s also very rewarding,” Matsumoto says. A scientist must have a good understanding of what has already been described, and must do a very thorough review of the existing literature in order to feel confident that the “new” species is in fact new to science and not just new to the scientist. “As with anything, you can’t know what’s new until you’ve spent some time looking at what’s already out there,” Raskoff says.

“Big Red” was first spotted on video during a submersible dive in 1993. In 1998, after several more sightings, Matsumoto was called in to identify it. He and Raskoff went back and pored over years of video footage to learn more about the animal’s typical size and geographic range. They also closely examined its anatomy for comparison with other known species. Big Red is unusual in that, unlike most jellyfish, it has no tentacles, only several fleshy arms to capture food. It is so different from other jellies that researchers ultimately assigned it to its own subfamily, Tiburoniinae.

Traditionally, biologists distinguished and classified jellies strictly according to physical shape: the number of tentacles, or a certain shape of the stomach. But this approach can be misleading, especially with jellies. “They can be very close cousins and look very different,” Raskoff says. “And things that look very, very similar can actually be very far apart, evolutionarily speaking.” It was years before scientists realized that polyps, small organisms that grow on surfaces such as rocks, are actually the immature form of free-swimming jellies. Matsumoto and Raskoff found that the number of arms on Big Red--often a reliable guide for distinguishing a species--varies anywhere from four to seven, depending on the individual.  

The advance of molecular biology has greatly aided scientists in their ability to identify and classify organisms. Ultimately, the taxonomy of organisms--how they are grouped in relation to one another--should reflect a common evolutionary ancestry. By examining and comparing DNA, which organisms inherit through reproduction, taxonomists have gained a much clearer picture of how organisms are related to one another across all taxonomic levels.

Recently, Raskoff and another MBARI scientist, Steve Haddock, have been taking a close look at the order Narcomedusae (phylum Cnidaria), a group of jellies that outwardly look very similar to one another. Based on physical appearance, scientists had previously declared certain Narcomedusae to be more closely related than others. But, says Raskoff, “the genetic evidence supports a very, very different linkage between these different groups. We found that the traditional taxonomy that has been accepted for hundreds of years for a large order of jellies turns out to basically be completely false.”   

Through genetic analysis, biologists are slowly gaining a better understanding of how and when the jellies evolved. Needless to say, fossils of jellies are few and far between. The evidence now suggests that jellies are an ancient life-form, hundreds of millions of years old, and probably predate most of the more familiar, complex animals. But many questions remain. For example, the comb jellies are typically classified into two types, those with tentacles and those without. Which type is older? Did the tentacleless kind appear first and the tentacled kind evolve later? Or did tentacles come first and then, in some comb jellies, disappear over time? Only further study and exploration will tell. What marine researchers know for certain is that the jellies they’ve discovered so far represent only a small fraction of what’s out there.

“We’ve been doing this for 15 years now, and yet we still see new stuff almost every dive,” says MBARI scientist Bruce Robison. “And that’s just in Monterey Bay. Our knowledge about the deep sea is still so poor that even after all these years of diving in this one spot, we still see new things all the time.”

Meanwhile, Matsumoto and Raskoff do their best to keep up. In addition to the several new jellies they’ve discovered in the past couple of years, they have perhaps ten more that look like solid candidates for new species. They’ll officially describe them, Raskoff says, just as soon as they discover something else: some spare time.