Jellyfish have been around for millions of years, even before dinosaurs lived on the Earth. Pulsing along on our ocean currents, these jelly-like creatures can be found in waters both cold and warm, deep and shallow and along coastlines, too. Some jellyfish are clear, but others are vibrant colours of pink, yellow, blue and purple. They can be bioluminescent, too, which means they produce their own light!

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.” 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.” 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. Bioflourescent jellyfish: Getty Images UK. Close-up of purple jellyfish: Bruce H. Obison. Jellyfish with long tentacles: Natursports, Dreamstime. Yellow jellyfish: Tim Hester, Dreamstime. Map showing jellyfish distribution: National Geographic Maps. Humans can also be stung by jellyfish which can result in mild symptoms such as pain and blistering, to more serious symptoms including whole-body illness. In some cases, stings can even be life-threatening. Bioluminescence

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.” Jellyfish are known for their sting! These animals have tentacles that have tiny sting cells on them called cnidocytes. These cells have tiny structures inside them that are full of venom, called nematocysts. When something touches a jellyfish these nematocysts shoot out and can penetrate the skin of the animal. The jellies use this mechanism to help capture prey or as a defense mechanism when they feel threatened.

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.

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.” 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. 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.” 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.

All 200 species of jellyfish exhibit radial symmetry. This means that they have a distinct top and bottom, but do not have a left or right side as all of their appendages radiate outwards from a central point, rather like the spokes of a bicycle wheel. A Mediterranean jellyfish. Jellyfish Reproduction 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. 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. 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. The jellyfish itself provides a tasty meal for other ocean creatures, particularly sea turtles, who like to guzzle them up regularly. In some cultures around the world, people eat jellyfish, too. In China, they are considered a delicacy, and are also used in Chinese medicine.

The Basics

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.” Like most venomous animals, the jellyfish inject their venom to cause pain and irritation. Jellyfish venom contains a type of protein called a porin which is responsible for the pain caused by their sting. This protein is not only found in the venom of all jellyfish but also in their relatives, including corals and anemones. The larvae settle on the seafloor and are now known as polyps. The polyps then begin to bud asexually and produce medusae which then develop into adults. Other true jellyfish species belonging to other genera may spend their lives solely as polyps or medusae and not alternate between the two different life stages in the same way. Jellyfish are one of the oldest animals on Earth and have changed very little from their prehistoric ancestors. These fascinating creatures have been studied by scientists for decades, increasing our understanding of the biological adaptations that have enabled them to persist in the world’s oceans for so long. Let’s take a closer look! Jellyfish Sting Unlike a lot of other animals, jellyfish don’t have a brain. They also do not have blood or a heart. Their nervous system which is known as a nerve net is very simple and allows them to smell, detect light, and respond to other stimuli.

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.” While in space, the number of jellyfish multiplied. On their return to Earth, the scientists examined these space-born animals and discovered that unlike Earth-born jellies, they couldn’t figure out how to deal with gravity. The light is produced by a chemical reaction between a chemical substance called luciferin and oxygen from the environment. This reaction releases energy and as a result, light is emitted. An enzyme called luciferase helps this reaction occur. For an animal to emit light regularly they must continually bring new luciferin into their system. Some animals acquire it through their diet while others can produce their own. 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. Bioluminescence is found in many marine organisms including around 1500 species of fish! Some species of sea stars, crustaceans, worms, and sharks are also luminescent. Moon jellyfish were sent into space by scientists who wanted to understand how they would respond to microgravity. Jellyfish in SpaceJellyfish are so cool they have even traveled into space! In 1991, some moon jellyfish were sent into outer space on board the Space Shuttle Columbia. This mission was a study conducted by scientists to understand how microgravity affected them. 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.”