WASHINGTON (AP) -- Living for days on end 63 feet beneath the waves is a near-ideal situation for researchers studying undersea life, biologist James Lindholm says. Yet sometimes the best-laid experiments can go awry.

Lindholm once found himself tracking a large grouper that unexpectedly ate the accompanying smaller fish he had tagged electronically so he could follow the big one.

"There's no substitute for being there," when studying sea creatures, Lindholm said Tuesday, and a prime way to do that is at the Aquarius undersea research lab in the Florida Keys.

A bevy of scientists and researchers spend up to 10 days underwater at the lab pursuing a variety of studies. Research this year ranges from studies of water pollution to astronauts-in-training to Navy rescue workers.

Lindholm, a research biologist at the Pfleger Institute of Environmental Research in Oceanside, California, will return there in November.

Aquarius is owned by the National Oceanic and Atmospheric Administration and operated by the University of North Carolina at Wilmington. Annual operation costs about $1.7 million.

Currently four scientists and two technicians are living in the space-station size environment 63 feet beneath the sea. Aquarius is 42 feet long and 10 feet in diameter, providing space for experiments, eating and bunks to sleep six. People in Aquarius spend most of their time outside, in the water.

Directed by Stephen Monismith of Stanford University, the current research group is studying the movement of nutrients in the water along the reef.

Mark Hulsbeck, Oceanographic Field Operations Manager for NOAA's Undersea Research Center, said the scientists are interested in the thermocline -- the border between warm surface water and cooler water below.

The cool water has more nutrients and the researchers using scuba gear can even observe waves in the border between the warmer and cooler water that break against the undersea reef much like surface waves break on the beach, Hulsbeck said via video connection from Aquarius.

Since the early 1990s more than 80 missions have worked from Aquarius and many more are planned.

A National Weather Service buoy floats on the surface above with a generator and pump to supply air and power to the undersea research center. Mission control is on nearby Key Largo.

Food is microwaved or boiled, similar to backpack food, Hulsbeck said, supplemented by things like fruit and cheese.

In June, Aquarius was the site of NASA space simulation training, an effort that agency calls NEEMO -- NASA Extreme Environment Mission Operations project -- echoing the name of Captain Nemo in Jules Verne's novel "Twenty Thousand Leagues Under the Sea."

It gives astronauts a chance to operate in an extreme environment, moving around with equipment in the water and living in about the same amount of space as the Russian unit of the International Space Station, said Marc Reagan of NASA.

It's also, like space, someplace they can't just jump back to land from, he noted.

Aquarius isn't as high as space or as deep as Verne's submarine, but it's at a depth that requires 17 hours of depressurization for divers who stay down more than a couple of hours.

That's because once a diver is in deep water for a time, inert gasses like nitrogen dissolve in the bloodstream because of the pressure, explained Andrew Shepard, director of NOAA's Undersea Research Center.

Come up too fast and the gasses can bubble out like the fizz from a soda bottle -- called the bends -- which can be painful and even fatal.

But, Shepard explained, once down for a few hours the diver's blood becomes saturated with the gases, no more will accumulate. That means they need the same amount of time to come up whether they are down for a day or a month -- so they generally stay 10 days or so doing lots of field work before returning, slowly, to the surface.

Other projects scheduled for Aquarius this year include Lindholm's fish study, another round of astronaut training and at least two sessions of Navy diving school.

• CNN article