When is a fish not a fish? When it's a jelly!

Black jellyfish usually live deep in the sea. But every five to eight years, they rise to the surface where they can be seen by humans.

Julianne Steers was aboard a 22-foot Boston Whaler in the Pacific Ocean when she saw them in the sea: rare black jellyfish.

Every five to eight years, black jellyfish – which normally live at ocean depths of 2,000 to 3,000 feet – rise to the surface. In the summer of 2005, a large number of black jellies surfaced off the coast of southern California, where Ms. Steers is a marine biologist at the Ocean Institute in Dana Point. They hadn't been seen in the area since 1999.

"Black jellies are a remarkable species, often growing up to a meter [about three feet] in bell size," says Ms. Steers. The "bell" is what some people call the body of the jellyfish.

When Ms. Steers spotted the black jellies, she collected a few and took them back to the lab. She hoped they would reproduce so that she and other researchers could study them. She was disappointed when they didn't – but she plans to try again the next time black jellies surface.

Until then, she has plenty of work to do with the aquarium's hundreds of moon jellyfish. These are one of the most common types of jellyfish.

Ms. Steers began investigating the interesting characteristics of the elegant white creatures when she started working at the Ocean Discovery Center at the University of California, Los Angeles. Later, when she worked at the Aquarium of the Pacific in Long Beach, Calif., a co-worker told her that some of the facility's moon jellyfish had small wounds caused when the jellies bumped up against the walls of their aquarium.

One day she removed a wounded jellyfish from the tank and put it in a small bowl by itself. Using a tiny pair of scissors, she removed the dead tissue. The jellyfish then regenerated its tissue. In other words, it grew new tissue to replace what she had removed.

Ms. Steers knew that jellies could make new tissue – but she was excited to learn that they could regenerate so much at one time.

Anatomy of a jelly

Just what are jellyfish, anyway? Well, they are not fish. Fish have skeletons, and jellies do not. Scientists also say that they don't have brains or hearts – but this hasn't affected the animals' survival. Jellies have inhabited the earth's oceans for more than 500 million years. There are more than 200 kinds of jellies, and most of them have a body shaped like a bell. From the bell's edges, tentacles hang down that stun or kill prey. "Oral arms," which dangle from the center of the bell, bring food to a jelly's mouth.

Some kinds of jellies are so small that the bell measures less than an inch across. And one of the biggest types of jellyfish, the North Atlantic lion's mane, can have a bell that grows up to eight feet in diameter.

Jelly tentacles grow to different lengths, too. The irukandji – a tiny jellyfish found off the coast of Australia – has tentacles that usually grow between one and 10 inches long. But the tentacles of the North Atlantic lion's mane can grow to more than 120 feet long.

Jellyfish live in every ocean in the world, and some even live in fresh water. Most jellies travel wherever the water current takes them. When they feel a slight pressure on their bodies – like the brush of tiny brine shrimp swimming past – coiled-up barbs (their stingers) eject, and a thread wraps around the object that applied the pressure. This is how jellies catch their prey. And "[t]hat's what you feel when you get stung," explains Ms. Steers. But she can't recall any stinging experiences. "I'm sure they've been stinging me, but I haven't felt anything!" she says.

In some places around the world this summer, jellyfish "bloomed" – their populations grew fast! Scientists aren't sure why this happened, but they have a few ideas. In some areas, the ocean is warmer – and that's ideal for growing some kinds of jellyfish. In other areas, there's more food available for jellies because the fish population is dropping, due to overfishing. Fewer fish mean less competition for the plankton that many jellies eat.

Too many jellies can cause problems, though. Big blooms of jellies can also break fishing nets or clog up boat generators. In a few cases, blooms have even forced coastal power stations to close down temporarily.

Jellies at the Ocean Institute

Moon jellyfish are a species easily found off the coast of southern California. The Ocean Institute exhibits these jellyfish in every stage of life, from tiny polyps – about the size of the head of a pin – to mature jellies.

Polyps are very young jellies. Instead of floating freely with their tentacles hanging down, polyps grow after jelly larvae have attached themselves to a rock or the seafloor, and their tentacles face upward.

Only after they get a little bigger do polyps detach and become free-floating, bell-shaped creatures. But then they aren't polyps anymore. They're on their way to being fully mature jellies.

And get this: One polyp can make clones of itself, which eventually launch into the ocean to become several adult jellyfish. Polyps can live for five years or more anchored to one spot.

Moon jellies are just one of 150 species of animals at the Ocean Institute, all of them local species. Many of them are obtained by Ms. Steers, who scuba dives nearby to look for animals to add to the exhibits.

"This job allows me to educate others about the marine organisms that live off our coast," she says. Ms. Steers hopes that people will use what they learn to "pursue better stewardship of our coasts."

So you want to be a marine biologist?

Do you want a job involving sea creatures when you grow up? JulianneSteers did, too. From the time she was little, she dreamed of workingwith ocean animals. She knew that was what she wanted to do even beforeshe knew there was a job called "marine biologist"!

Whenshe grew older, she attended the University of Arizona, Tucson, whereshe studied ecology and evolutionary biology – areas of study notoffered at every school. Even though her university was far from theocean, Ms. Steers took as many marine biology classes as she could. Sheoften went down to a seaside field station in Mexico to study seaanimals, too.

She took advantage of the labs – hands-onactivities connected with classroom lectures – so she could get plentyof experience working with animals. And she went on every field tripoffered so she could get experience in the field.

Evenbefore she got to college, she had focused on her career goal. When shebecame old enough to get a summer job, she was an assistant to one ofher former teachers in a kids' science program.

Whileshe was a college student, Ms. Steers worked and volunteered atdifferent places during the summers. One day she saw notices near whereshe lived that the Ocean Discovery Center of UCLA would soon beopening.

That was all the inspiration she needed. Evenbefore the facility was open to the public, she was working there! (Thecenter is now called the Santa Monica Pier Aquarium.)

Ms.Steers ended up helping out at the center every summer for severalyears. Sometimes she did paperwork, which was not too exciting. But shealso got to work with the animals and learn what it would be like to bean aquarist.

She also volunteered at the Cabrillo MarineAquarium's jelly research lab. One internship, at the Marine MammalCare Center at Fort MacArthur in San Pedro, Calif., gave her experienceworking with seals and sea lions.

"I had one unpaidinternship where I worked probably 60 [or] 70 hours a week," says Ms.Steers. "I'd come at least four or five days a week for at least eightor nine hours, sometimes 12 or 14 hours.

"I wanted to get as much out of every experience as possible. It's much better to be hands-on."