Sitting at a table 50 feet under the sea, legendary ocean explorer Sylvia Earle lamented what she believes is a shortsighted federal decision to cut off funding for the world’s only undersea laboratory.

She was speaking by phone from the Aquarius Reef Base off the coast of Key Largo. She was one of a handful of researchers participating last week in the last federally funded mission to the Aquarius. The budget for the National Oceanic and Atmospheric Administration’s national undersea research program is slated to be eliminated, to the dismay of many researchers.

“For science, we really need assets to keep eyes on the sea, not just a few glimpses here and there,” said Earle, a National Geographic explorer-in-residence. “We need to understand what we’re doing and how to stabilize the systems that are keeping us alive.”

Deployed in the Florida Keys National Marine Sanctuary two decades ago after a four-year stint in the U.S. Virgin Islands, the laboratory has hosted 117 missions since 1993. The 81-ton yellow tube holds six bunks, a galley, a bathroom, a science station and a “wet porch,” where scuba-diving researchers enter and exit. Visitors can stay for up to two weeks with no worry of getting the bends, because the air inside the Aquarius is pressurized.

Researchers, who dive up to 12 hours a day, have used the platform to investigate everything from how sponges change the ocean’s chemistry to the way water flows over a reef.

But the federal budget crunch and cost overruns in NOAA’s satellite program have put pressure on the “wet side” of the agency’s budget — its ocean programs. Funding for the national undersea research program plunged from $7.4 million in fiscal year 2011 to $3.98 million in fiscal 2012, before the administration slated it for elimination in fiscal year 2013.

By contrast, NOAA has asked for more than $2 billion to fund its weather satellite program in 2013 — a $163 million increase from the current fiscal year.

Former NOAA administrator Conrad C. Lautenbacher Jr., who headed the agency under George W. Bush, called the decision to cut off funding for the Aquarius “penny-wise and pound-foolish.” He said the station — which runs on between $1 million and $4 million a year, depending on the number of missions — also gives NASA astronauts a chance to practice how to operate in space.

“It is a national asset. It’s not a large expense, but it’s very valuable for the entire national picture,” Lautenbacher said. “You have to have priorities, but to put the oceans at the bottom all the time is a very bad thing to do.”

In a statement, NOAA Administrator Jane Lubchenco, a marine ecologist by training, said the Aquarius “has been a vital part” of the agency’s oceans research “and we fully recognize its importance.”

“NOAA’s core mission is to conduct and support scientific research and exploration of the oceans,” she said. “Unfortunately, our budget environment is very, very challenging and we are unable to do all that we would like.”

The lab was vulnerable to the budget ax in part because it is part of a grant program; although the Aquarius is owned by NOAA, it is run by the University of North Carolina at Wilmington. Thomas Potts, the lab’s director, said that the program sustained “tremendous cuts” in 1996 and 2006, but that this time is different: “Now there is actual legislative language which says boom, let’s kill this.”

Rep. Ileana Ros-Lehtinen (R-Fla.), the lab’s fiercest proponent in the House, went diving Saturday to visit the lab with her husband, Dexter, and Rep. Mario Diaz-Balart (R-Fla.). A third lawmaker, Rep. David Rivera (R-Fla.), snorkeled as part of the same event.

Ros-Lehtinen said that only private donations through the newly created Aquarius Foundation could keep the facility operating.

“As NOAA funding ends for this innovative laboratory, we are all hopeful that an Aquarius Foundation will be able to reopen the base to continue the important scientific studies undertaken there,” she said.

Mark Patterson, a College of William and Mary marine science professor whose visit to the Aquarius last month marked his eighth visit there, said researchers like himself can learn much more by immersing themselves in an aquatic environment. For example, working for days at a time underwater, he said, they can attach probes to tiny coral polyps to monitor such things as the ocean’s acidity and the way water moves.

“We’re wiring up the corals to have them tell us their secrets in a way we never can in the lab,” Patterson said. “It’s just such a better way to do science, to do it in the ocean rather than concoct a caricature microcosm of nature in the laboratory. . . . I hope we’re not all crying as we turn out the lights, because working underwater is one of the most interesting things I do.”

Before the mission ended Saturday, the Aquarius hosted journalists and a film crew from the group One World One Ocean, which produced several videos about the lab.

“I think a lot of people don’t know what we have here,” said Shaun MacGillivray, One World One Ocean’s managing director, adding that being in the Aquarius “feels like you’re in outer space.”

Potts said he hasn’t given up hope, especially after hearing Lubchenco talk about the predicaments of coral reefs at the International Coral Reef Symposium this month in Cairns, Australia. The Aquarius sits next to Florida’s Conch Reef.

“Here it is, the case study, so now’s not the time to pull the plug on these things,” he said. “Now’s the time to invest.”