– Just off the rocky shoreline, in the mile-and-a-half gap between Plum Island and Long Island’s Orient Point, the open Atlantic meets Long Island Sound.

The fierce currents of Plum Gut, as the area is called, carry all sorts of nutrients and marine life, drawing multitudes of small bait fish. Those, in turn, lure larger predators: striped bass, squid, bluefish and seals. Whales and sea turtles have been spotted there, and avian hunters include osprey, cormorants and tens of thousands of common and roseate terns that nest nearby.

“It’s one of the largest fish concentrations in the entire mid-Atlantic area,” said Chris Cryder, a project coordinator for the Connecticut-based environmental group Save the Sound.

The astonishing variety of birds, fish, animals and insects that live on and around the 840-acre Plum Island don’t care that it’s also home to an infamous federal institution. A maelstrom of conspiracy theories and rumors about Nazi scientists, extraterrestrials and biological warfare still swirls around the Plum Island Animal Disease Center, and the insistent denials from federal officials mean nothing to the surrounding sea life.

Far more important to the future of all those wild creatures, environmentalists warn, is what will happen to their island refuge once the federal research laboratory leaves?

Construction has now begun in Manhattan, Kan., on a $1.25 billion, high-security replacement lab that will study virulent animal diseases, and Congress has mandated that Plum Island be sold to the highest bidder. The move is scheduled to take place by 2024.

For more than 60 years, the presence of the animal disease laboratory and the armed security that surrounds it has preserved the rest of the island and its nearby waters from human disruption. The lab occupies barely 20 percent of the island, and the remnants of century-old military forts and batteries are now crumbling and overgrown.

There have been estimates that selling the island could reap anywhere from $32 million to $100 million from potential developers. Donald Trump once speculated that the island might be a great location for exclusive golf courses.

What might happen to the island and the marine ecology of Long Island Sound is anyone’s guess and the stuff of nightmares for naturalists. “The whole system is so interconnected,” said Suzanne Paton, a marine biologist with the U.S. Fish and Wildlife Service.

The fate of the island is also important to Connecticut.

“People in this state should care about Plum Island because it is part of the Long Island Sound ecosystem,” said Tom Anderson, a spokesman for the Connecticut Audubon Society. “Any development out there could jeopardize the marine environment.”

The idea that Plum Island could end up in private or commercial hands has sparked protests from environmental groups, community activists, and politicians in New York and Connecticut, and threats of legal action to block the planned sale.

There are economic questions, as well, with about 400 high-paying jobs at stake, half for Connecticut residents and half for New Yorkers. The federal government, by some estimates, is spending more than $56 million a year on the Plum Island research operations.

“It really is a regional as well as national and even international issue,” Cryder said. His organization is part of the Preserve Plum Island Coalition.

Claims about international implications are more than just hype. The 9,500 pairs of common terns that nest on nearby Great Gull Island make it the largest such breeding site for that species in the world, ornithologists say. And the 1,300 pairs of roseate terns make the area the biggest and most important nesting location for that bird in the Western hemisphere. The roseate tern is an endangered species. The birds forage for fish off the shores of Plum Island and use its rocks and beaches to rest, shelter and raise fledglings. The endangered piping plover also nests on the island.

Save the Sound, which also has New York affiliations, filed notice this year of its intent to sue the U.S. Department of Homeland Security and the General Services Administration, the two agencies that have responsibility for Plum Island and its sale. The lawsuit alleges that federal officials have failed to properly ensure protections for threatened and endangered species.

Federal officials point out that environmental impact studies were conducted, that proper procedures to approve the sale have been followed, and that they are working under a congressional mandate.