The lab allows the scientists to live and work on the seafloor, giving them longer blocks of time to study reefs than conventional scuba diving would allow.

"If you're a coral reef biologist, you've got to dive. You've got to spend time in the environment that you're studying. And conventional scuba diving is really limited. You work from the surface; you have maybe an hour a day. Imagine trying to do your job if all you had was an hour a day," Steven Miller, director of the University of Wilmington's National Undersea Research Center, told the NewsHour.

The 81-ton facility -- owned by the National Oceanic and Atmospheric Administration and operated by the University of North Carolina at Wilmington's National Undersea Research Center -- is currently located 9 miles southwest of Key Largo, submerged 63 feet on a sandy patch in the Florida Keys Marine Sanctuary next to Conch Reef.

Scientists studying in Aquarius, nicknamed "aquanauts," can work underwater for up to 14 days and dive for up to nine hours a day. Aquanauts are able to avoid the restrictions of conventional scuba diving through saturation diving, a diving technique that allows nearly unlimited time to work underwater.

A saturation dive is "an exposure of sufficient duration so that the diver's tissue gases reach equilibrium with the pressure environment," according to NOAA's Diving Manual. Saturation diving allows aquanauts to live and work at ambient pressure, (the pressure at Aquarius' working depth is 2.5 times surface pressure) for months at a time.

The practice is based on the fact that after 24 hours at any working depth, a diver's body becomes saturated with dissolved gas from the environment. Once saturated, decompression -- the time necessary to return the diver progressively back to surface pressure -- is the same regardless of the amount of time spent underwater.

"The Aquarius essentially allows you to extend the time at depth indefinitely so you can make much more detailed observations. And this makes a tremendous difference in our level of understanding how things work," John Ogden, director of the Florida Institute of Oceanography, told the NewsHour.

At the conclusion of an Aquarius mission, aquanauts undergo a 17-hour decompression period where the pressure inside Aquarius is gradually reduced to meet surface pressure. The aquanauts then swim to the surface and are taken back to shore.

The bright yellow undersea lab consists of three main system components: the Life Support Buoy, the baseplate and the "habitat" module.

The LSB moored above Aquarius contains compressors, generators and a communication tower that provides audio, video, and data transmissions between Aquarius and shore. It contains Aquarius' oxygen hoses and power and communication lines.

A 116-ton baseplate provides a stable platform for Aquarius. Each of its four legs can adjust for leveling Aquarius on uneven seafloor terrain by using hydraulically driven screw jacks. The laboratory is then mounted about 47 feet off the seafloor. This operating depth is called the "hatch depth."

Aquanauts live and work inside the Aquarius "habitat" module, a 43-foot-long, 9-foot-wide structure that can house a six-person crew and can operate at a depth of up to 120 feet. The living quarters contain a sleeping area, kitchen, computer workstations and life support controls. Modes of communication with the outside world include e-mail, telephone and video conferencing.

Scientists enter the habit through a nonpressurized 8-foot-long "wet porch," which provides access from the sea to Aquarius. The wet porch remains open to the ocean, and water remains outside Aquarius by the equivalent air pressure inside.

Next to Aquarius is the Gazebo, which provides a safe place in the event of an emergency within the habitat. The Gazebo has an enclosed aluminum roof with 60 cubic feet of air, which is enough room for six aquanauts.

In Key Largo, a shore-based Mission Control contains a "watch desk" linked to Aquarius via a telemetry system.

Four scientists and two technicians stay aboard Aquarius during a single mission, but the support crew is much larger.

According to Jim Leichter of the Scripps Institution of Oceanography, "There's a very large support crew. And so when you're out diving, there's a constant activity of equipment being brought down from the surface."

Additional scientists at Mission Control oversee each mission.

Since its launch in 1988, more than 200 scientists have stayed in Aquarius on over 50 missions designed to better understand our oceans.

Leichter said Aquarius allows scientists to do "the best possible science" by seeing a larger view of the coral reef system. Research proposals are submitted to the program annually and are chosen through a peer-review process.

Past research includes pollution studies, water quality studies, human effects on coral and ultraviolet light's damaging effects on reefs.

NASA crewmembers have stayed in Aquarius to help prepare for journeys into deep space. And doctors with NASA's Extreme Environment Mission Operations, or NEEMO, have studied the possibilities of remote surgeries using Aquarius' telecommunication technologies.

Marine biologists aboard Aquarius are studying ways to preserve coral reefs, working to steadily build their knowledge of these complex ecosystems.

An estimated 20 percent of the world's coral reefs have been destroyed, and in the United States Caribbean and Gulf of Mexico region, 56 percent of the reefs are in critical condition, according to the 2004 Status of the Coral Reefs of the World report written by the Global Coral Reef Monitoring Network and the International Coral Reef Initiative.

"It's not like there's a magic bullet, a silver bullet if you will, that once we find this one spectacular piece of information we're going to save the reefs. That won't happen. What we need is a long-term sustained effort at trying to understand all the factors that affect the condition of the reef," Miller said.

(Click here to visit NOAA's Aquarius Web site.)

-- By Katie Mulik, NewsHour