BISCAYNE NATIONAL PARK, Fla. – Richard Curry remembers when the waters in this 173,000-acre preserve were teeming with fish and vibrant corals.

“It was gorgeous. There were fish all over the place, lobster all over the place; there was color in the corals,” said Curry, who has worked in the park for 27 years and is its science research coordinator.

But on a recent snorkeling trip, Curry pointed out that the ventilina, a fanlike coral that should be bright purple, is now a dull brown, and just a few fish were visible among the reefs. The average size of black grouper in the park has shrunk 60 percent since 1940, and the total population of the threatened reef fish has dropped 95 percent, mainly because of overfishing.

“The whole system is in jeopardy – there’s no question,” he said.

The question of what to do in Biscayne is part of a larger scientific and political debate about imposing limits on marine resources. Many marine experts are suggesting that 20 percent to 30 percent of the seas should be “no take” – off-limits to fishing, drilling and other habitat-disturbing activities – but less than half a percent of the oceans are now fully protected.

The United States has several levels of protected marine areas. Reserves generally ban invasive practices such as fishing or lobstering, while sanctuaries and marine parks make resource protection their highest priority but allow some recreation and commercial uses.

There are 13 marine sanctuaries from Massachusetts to American Samoa, spanning 18,600 square miles, or 0.004 percent of U.S. waters. Only 220 square miles are no-take reserves, all of them in the Florida Keys National Marine Sanctuary.

Groups such as the Ocean Conservancy and the National Parks Conservation Association have called for creating no-take reserves in Biscayne National Park, which is part of the Florida Keys under the Park Service rather than the sanctuary program. They cite a 2002 academic study of Biscayne that called the waters “seriously overfished,” adding that without more active management, “collapse of many important fisheries resources appears imminent.”

But when some park managers raised the idea of creating no-take reserves in what the park’s resource manager, Rick Clark, calls “Miami’s playground,” they were rebuffed.

State and federal officials, Curry said, “bowed to political pressure. A lot of people don’t like closures.”

David White, director of the Ocean Conservancy’s southeast regional office, said, “It’s where the ship of science is foundering on the shoals of politics.”

Recreational and commercial fishing groups have often opposed marine reserves. Edwin Roberts, former chairman of the Florida Fish and Wildlife Conservation Commission, minced no words at a March 2003 meeting when he said the idea of banning fishing “makes the hair stand up on the back of my neck. I just can’t stand that.”

Jim Donofrio, executive director of the New Jersey-based Recreational Fishing Alliance, said his 90,000 members support some fishing restrictions but are “completely opposed to marine reserves, which mean no take forever. … There’s not enough science out there to prove the value of them. The fish swim in and out of them.”

No-take reserves are not a cure-all – they do not address problems such as pollution and rising temperatures – but several recent studies suggest they can help restore fish populations and damaged ecosystems. In 1994, after fisheries collapsed in the Gulf of Maine’s Georges Bank, for example, federal authorities prohibited groundfish fishing and dragging for scallops in three areas spanning 6,600 square miles. Within five years, haddock and witch flounder stocks rebounded, while scallops grew bigger and became nine to 14 times more dense than in fished areas.

Andrew A. Rosenberg, who oversaw the Georges Bank recovery plan as a Fisheries Service regional director and is now a professor at the University of New Hampshire, now tells his friends to order scallops when they dine out.

“Marine-protected areas are a blindingly obvious, very effective tool,” Rosenberg said. “You need to leave some places alone.”

Some marine advocates are seeking a middle ground, pushing for sanctuaries or other marine limits that stop short of no-take reserves. The nonprofit group Environmental Defense has been working with regional fishery officials to identify 700 square miles between North Carolina and Florida where only bottom fishing would be banned to restore deep-water grouper and snapper stocks, as well as another plan to protect coral forests.

David Festa, ocean program director at Environmental Defense, said negotiations took off after people “let go of the holy grail of no-take marine reserves.”