Imagine standing on the bottom of the ocean and looking up into a glittering kelp forest alive with darting fish, or watching five-foot-long sharks and giant tuna whiz by at arm’s length, or being surrounded by elegant, lacy white jellyfish as they soar, pulsing, through the water. Visitors to the Monterey Bay Aquarium on the coast of Northern California experience all this… and more.

For more than 20 years, the Monterey Bay Aquarium has entertained, educated, and fascinated its nearly 2 million annual visitors with pioneering displays of realistic undersea environments. Now NATURE gives viewers a behind-the-scenes look at one of the world’s leading centers for marine research and conservation — a marvel of engineering and biology that, literally, captures Oceans in Glass.

To order a copy of Oceans in Glass: Behind the Scenes of the Monterey Bay Aquarium, visit the NATURE Shop.

Online content for Oceans in Glass was originally posted January 2006.

Walk into the Monterey Bay Aquarium and you may find yourself surrounded by a ghostly swarm of luminous, pulsing phantoms. The specters are actually moon jellies — common marine creatures — swimming in darkened, mirrored tanks that give visitors the illusion of strolling through a shadowy ocean. “It’s a marvelous feeling — people love it,” says aquarium biologist Dr. Randy Kochevar, who appears in this week’s NATURE: Oceans in Glass: Behind the Scenes of the Monterey Bay Aquarium.

Moon jellies, however, are just one species in the aquarium’s dazzling collection of jellyfish — boneless, gelatinous creatures that may be warning us of trouble in the sea.

Jellies live in virtually every part of the ocean and come in a dizzying array of shapes, sizes, and colors. Some, like the aquarium’s box jellies, are no bigger than a thimble. Others, like the Arctic lion’s mane, have umbrella-shaped bells that reach 7 feet across and tentacles that stretch 100 feet or more. Jellies often use their tentacles to sting and snare prey, such as small fish, while drifting with the current. The flower hat jelly, another species on display in Monterey, has even grown a colorful tentacle fringe to help it lure in prey.

Not all jellies rely on their tentacles for food. Some have joined forces with specialized microorganisms that live beneath their bells. These cooperative jellies simply turn upside down and rest on the bottom of shallow seas, letting their guests soak up the rays and produce food. In tropical waters, it’s not uncommon to see thousands of these inverted, sun-loving jellies on the sea floor, creating a scene that looks a bit like a marine flower garden.

In some waters, however, an explosion in jelly populations, or blooms, has scientists worried. They say more jellies may ultimately be a sign of fewer fish — and a less healthy ocean.

One of the first warnings came more than 20 years ago, when researchers studying the Black Sea, which straddles Eastern Europe and Asia, began to notice huge numbers of a jellyfish named Aurelia aurita. They suspected these massive blooms were due to increasing pollution and massive irrigation projects that reduced the amount of fresh water flowing into the Black Sea, making it saltier.

Soon, the scientists found that the jellies were eating up to two thirds of the sea’s zooplankton (microscopic animals), which meant they were competing directly for food with several kinds of commercially important fish, including anchovies. A number of researchers believed this competition was one reason anchovy stocks had begun to dwindle.

Some help arrived in the late 1980s, when engineers increased the amount of fresh water flowing into the Black Sea, making conditions less favorable for the jellies. But the story wasn’t over. Cargo ships apparently carried another kind of jelly — a species typically found in the Atlantic — into the Black Sea, where it also began blooming in huge numbers. Ultimately, the two species began to alternate, with one numerous in some years and the second swarming in others.

As a result, “nearly all of the zooplankton production in the Black Sea appears to have gone from feeding fishes to feeding jellyfish,” concludes marine biologist Claudia Mills of the University of Washington, a leading expert on the organisms. She also believes that the jellyfish may be one reason anchovy populations remain low.

Mills and other scientists have also documented unusual jelly blooms closer to home, in the waters off Alaska and New England. In recent years, the Gulf of Mexico has also been plagued by invasions of a spotted jelly native to the Caribbean. Few people have ever seen them in such numbers — swarms so big that Gulf states have been forced to shut down parts of a shrimp fishery worth tens of millions of dollars.

The jellies are so thick that “the weight stops even a 90-foot boat cold,” one shrimper told the magazine One Earth. “It’s like crashing into a brick wall. You can’t go forward. You can’t back up, because the nets get tangled in propellers. And the nets are too heavy with jellyfish to even pull them up.” Some scientists even joke that, the way things are going, people will need to start eating jellies instead of fish or shrimp.

On a more serious note, researchers contend that the causes of jelly blooms are often mysterious, although overfishing, pollution, and climate cycles are probably playing a role. In part, the mystery is due to a lack of understanding of basic jellyfish biology. Scientists don’t know exactly how many species live, breed, and survive. At the Monterey aquarium, researchers are solving some of these riddles by raising jellies for display in a specialized “jelly farm.” The tanks allow scientists to fiddle with everything from water temperatures to food supplies to find the perfect conditions the creatures need to thrive. Eventually, they say, such studies could reveal what these ghostly, pulsing organisms are telling us about the health of the ocean.

In the early dawn of March 31, 2005, researchers from the Monterey Bay Aquarium made history. Standing on a small boat far off the coast of California, they carefully lifted a sling carrying a six-foot-long great white shark over the side and — splash! — the powerful fish was back in the wild, after spending a record 198 days at the aquarium.

As NATURE’s Oceans in Glass shows, displaying a great white — one of the sea’s most impressive predators — has long been a dream of aquariums around the world. But previous efforts to care for the sharks — which can grow to weigh two tons and measure 21 feet long — have largely ended in failure. The great whites proved too big, too aggressive, or too sensitive to live penned up. Some wouldn’t eat, says biologist Dr. Randy Kochevar of the aquarium, “and sharks can’t survive long if they aren’t feeding.”

In Monterey, however, biologists working on the aquarium’s shark conservation and ecology project believed it was possible for a great white to survive — and thrive — in one of the facility’s giant display tanks. They also believed that letting the public see these magnificent hunters up close could pay big dividends for their efforts to protect sharks, which are under increasing threat.

With this goal in mind, several years ago the aquarium’s researchers began experimenting with ways to keep a captive shark happy. First, they built an enormous 4-million-gallon pen in the ocean off Malibu, California. When commercial fishing boats accidentally caught a great white, the aquarium arranged for it and several others to be moved to the pen. There, researchers learned to feed the sharks and understand how they behaved in captivity.

Those lessons bore fruit in August 2004, when a commercial halibut fisherman caught a young, five-foot long female great white in the waters off Huntington Beach. After being held in the Malibu pen for three weeks, she was moved to the aquarium for display. Over the next six months, nearly one million people came to see her. “She was an incredible ambassador for white sharks and shark conservation,” says Kochevar.

But the young shark was also growing bigger and more restless. “She basically grew more than a foot and gained 100 pounds,” according to Kochevar. “And one day she apparently decided she needed to increase the breadth of her diet,” which consisted mostly of salmon and other fish fed to her by aquarium staff. The great white began stalking other animals in the tank, eventually attacking two smaller soupfin sharks. The staff decided it was time to release the growing animal back into the wild, but not before she provided one last service to science.

This great white shark was at the Monterey Bay Aquarium for about six months.

On their way to the release site, researchers attached a sophisticated electronic tag to the shark that would record her movements for 30 days and then pop off, transmitting its location to a satellite for retrieval. Similar tags have helped revolutionize our understanding of the habits of a myriad of animals, from sharks and sea turtles to seals and bluefin tuna. Indeed, the aquarium is part of an innovative effort — called the Tagging of Pacific Pelagics (TOPP) project — that is harnessing all kinds of marine animals to carry sensors into the ocean.

In the great white’s case, the tag worked perfectly. After popping off the shark on schedule, the tag was retrieved from surly seas off the coast of Santa Barbara by Stanford University doctoral student Kevin Weng. “They lose container ships out there!” he exclaimed after using a long-handled net to scoop the tag out of the whitecaps.

The researchers say the tag showed that after being released, the shark swam more than 100 miles offshore and to depths of greater than 800 feet. “It’s clear she survived and thrived,” says Kochevar, adding that the shark first swam several hundred miles south along the California coast, “then took a hard right and headed offshore for a while, then returned to the coast. … There’s no question that she was hunting and feeding on her own.”

Similar data from other young sharks is beginning to give scientists a picture of how these animals use the ocean and how people could improve conservation efforts, according to Kochevar. There is little question that the great white’s brief stay at the Monterey Bay Aquarium has helped stoke public support for shark research and conservation, he adds. Not long ago, the aquarium’s trustees decided to increase their shark research budget by half a million dollars.

To learn more about the TOPP project, visit http://topp.org/.

Some tuna are good sustainable seafood choices. But others such as bluefin tuna are overfished and should be avoided.

With nearly three quarters of the world’s fish and seafood stocks now fully exploited or overfished, it’s increasingly important for consumers to understand how their seafood dinner can contribute to the health — or degradation — of the ocean.

To help consumers make informed decisions, the Monterey Bay Aquarium has started the Seafood Watch program. It offers consumers tips on buying environmentally friendly seafood through a Web site and easy-to-carry pocket guides. “It’s been a staggeringly popular program,” says the aquarium’s Dr. Randy Kochevar. “We just passed the 5 million mark of people downloading the guides, and studies show that people do carry and use them.”

What do consumers need to take into consideration when they decide to serve shrimp, for instance? Researchers say that for every pound of shrimp that reaches your plate, up to 10 pounds of other kinds of marine life, from sea turtles to baby sharks, gets caught in trawl nets and thrown away. Worldwide, such “bycatch” constitutes up to a quarter of the total seafood netted and has had deadly effects on marine populations, including seabirds that get snagged on hooks and dolphins that drown in nets.

So what kind of shrimp should you buy? According to Seafood Watch, one good bet might be the smaller variety found in northern waters, typically sold as “salad shrimp.” They reproduce faster, and the fishing methods used to catch them are relatively eco-friendly. In particular, pink shrimp caught off Oregon are one safe bet identified by Seafood Watch.

The program also highlights fish species to avoid. Orange roughy and Chilean sea bass, for instance, are two deep-water species that have been seriously overfished. Because they are long-lived and reproduce slowly, it takes a long time for their populations to bounce back. In addition, they are caught using bottom-dragging trawl nets that can also damage seafloor communities. And for those concerned about their own health risks, Seafood Watch says there is another reason to avoid the roughy — it can be high in mercury, a toxic metal.

Although Seafood Watch has been effective, the aquarium is now ready to take its environmentally safe seafood campaign to the next level, by reaching out to the market and restaurant owners who buy large amounts of fish, shrimp, and shellfish. “We need to move further up the food chain,” Kochevar says. “Consumers are important, but the purveyors also need to understand how to make sustainable choices.”

If you’d like to learn more about Seafood Watch, visit http://www.mbayaq.org/cr/seafoodwatch.asp.