Why Jacques Cousteau's grandson will spend 31 days underwater

The grandson of famed oceanographer Jacques-Yves Cousteau will embark on a month-long stay inside an undersea laboratory off the Florida Keys in an attempt to break a half-century-old record set by his late grandfather.

After years of planning and delays, Fabien Cousteau will make a 60-foot (18-meter) dive on Sunday in an attempt to spend 31 days in a laboratory known as Aquarius, observing fish behavior, studying the impact of ocean pollution and warming seas on coral reefs, and measuring the effect of lengthy underwater stays on the human body.

"There are a lot of challenges physically and psychologically," said Cousteau, 46, who was born in Paris and grew up on his grandfather's ships, Calypso and Alcyone.

"The benefit is that the backyard is infinite."

Cousteau will be living and working underwater with a team of researchers and documentary filmmakers. If he succeeds in spending the entire time submerged, Cousteau will beat the 30-day underwater record set 50 years ago in the Red Sea by his grandfather.

The cylindrical 43-foot (13-meter) Aquarius is the last undersea laboratory still operating. It sits on a patch of sand near deep coral reefs about 9 miles (14.5 km) south of Key Largo, Florida.

It is "the best-kept secret in the oceans," Cousteau told Reuters in 2013.

Dozens of other undersea labs around the world have been mothballed due to high costs. In 1963, Jacques-Yves Cousteau along with a half-dozen divers he dubbed oceanauts spent 30 days inside an undersea lab called Conshelf II near the Port of Sudan.

Aquarius is air conditioned with wireless Internet access, a shower, a bathroom, six bunks and portholes that give the occupants a 24-hour view of the surrounding marine life.

The living space is at a depth where the atmospheric pressure is roughly two-and-a-half to three times that at the surface. It will be pressurized to prevent decompression sickness, when human tissue absorbs gases like nitrogen in dangerously high volumes.

Beyond the otherworldly experience, the benefit of living underwater is it will help scientists with their day-to-day research and data collection.

Researchers studying the effects of coral bleaching - when warming waters prompt the living coral to expel the colorful algae living inside - will depart Aquarius at the crack of dawn each morning to study the reefs' energy production before the day begins.

"Day in, day out, our science schedule is pretty repetitive. I think the documentary guys are going to get bored," said Andrew Shantz, a Ph.D. candidate in marine ecoscience at Florida International University, who will spend 17 days in the lab.

Following the morning dive, teams will return to the station to speak via Skype with classrooms around the world and test how the extended stay at depth affects their bodies.

They will re-emerge from Aquarius in scuba gear around noon and after night falls to collect additional data that would be impossible without the underwater lab.

"You end up getting these structured, regimented observations that you don't get on a single dive," Shantz said. (Editing by Kevin Gray and Jan Paschal)