Study of Plum Island’s pristine waters reveal rare Long Island habitat

The Plum Island waters are a plum.

That’s the gist of a scientific diving team’s findings, based on a report of a 2021 survey of Plum Island’s marine habitats.

“Some of these habitats are really rare,” New York Natural Heritage Program marine zoologist Meaghan McCormack said during a webinar last Thursday night in advance of the report’s release the following day. “We don’t have many of them on Long Island. You know, eelgrass is decreasing, rocky, intertidal areas, we don’t have much, and these areas right off the rocky, intertidal, these subtidal areas that have these large boulders are really unique and just for one small island to have all these different communities surrounding it is really special.”

A four-member scientific dive team made 27 dives over five days in Plum Island’s biologically rich, pristine waters Aug. 2-6, 2021, collecting samples, recording data and analyzing what they found in the island’s underwater ecosystem.

Their findings were published in a 33-page report titled, “Survey of Plum Island’s Subtidal Marine Habitats.” The report, prepared by the NYNHP and InnerSpace Scientific Diving and sponsored by Save the Sound, stated, “The physical oceanography of the area and lack of development on Plum Island make the region unique compared to the rest of Long Island.”

Plum Island’s waters had been a relative mystery until recently. The 2021 dives were a more in-depth followup to similar dives in 2019.

Scientists marveled about the diverse habitats supporting an abundance of life they found in those waters. Steven Resler of InnerSpace Scientific Diving, one of the 2021 scientific divers along with Janet Klemm, Dan Marelli and Dave Winkler, told reporters on the final day of those dives that the waters were a “wow” site because of the numbers and the diversity of both fauna and algae found.

“I would say it’s a microcosm, a mini-Long Island,” Mr. Resler said last Thursday night. “Every environment that you would find around Long Island, you got around Plum Island in one small area.”

A good deal of the explanation for Plum Island’s intriguing marine ecosystem can be found in the 822-acre island’s history and location. The federally owned island, a part of the Town of Southold and about one and a half miles off the eastern tip of Orient Point in Gardiners Bay, is closed to the general public.

The United States Department of Agriculture established a facility on Plum Island in 1954. It was used by the Army and as an animal disease laboratory. The animal research facility was to be relocated to Manhattan, Kansas, when the Department of Homeland Security put the three-mile-long island up for sale in 2008, but it was taken off the auction block in 2020 amid development concerns.

Save the Sound leads the Preserve Plum Island Coalition, a membership made up of 120 national, regional and local organizations that have been working to ensure the island’s permanent conservation.

The Plum Island waters are continually churned up by the convergence of Long Island Sound, Block Island Sound and the Peconic estuary “so it sits in an interesting junction of environments,” said Dr. Matthew Schlesinger, the NYNHP chief zoologist.

Photos and videos were shown of what the divers saw last summer when they worked in the murky waters, struggling with strong, restless currents.

“Currents exist at all times, and there is no slack tide around Plum Island,” Mr. Resler said. “Once below the surface, you can have currents running in two different directions only five feet apart in depth … and you can’t usually swim against it. It will push you from one side to the other … so it’s not an easy place to dive.”

But the scientists, diving in depths of 30 to 10 feet, found the struggle well worth it. They saw a lot of life in those waters as they swam between massive stone boulders, some up to 25 feet in diameter. Some of what they saw: jellyfish, crabs, seals, anemones, bryozoans, starfish, coral, algae-covered boulders, kelp being grazed upon by snails, juvenile sea bass, macroalgae, worms.

And sponges. “We found them everywhere,” said Mr. Resler.

Video showed a starfish walking slowly across the bottom on hundreds of tiny feet under each of its arms, moving in unison.

Bryozoans look like skinny, long shrimp and are “kind of freaky looking,” said Mr. Resler. He said: “Bryozoans are on everything, every hard substrate, everywhere. They are, to me, the greatest influencers here … They provide cover for all manner of fish and other species.”

Altogether, 126 species of plants and animals were identified, more than twice as many as from the 2019 dives, said Ms. McCormack.

“We didn’t find one piece of trash, one bottle, one bottle cap, not even a piece of fishing line on the bottom,” Mr. Mr. Resler said.

What they didn’t find: evidence of human intrusion.

Gray seals and harbor seals were visible to the divers only if the seals were on the surface or close to them. “They’re there, they come close — you just don’t see them,” said Mr. Resler.

Mr. Resler said a mesh sample bag had gone missing. The divers searched for it and when they rose to the surface, they saw the likely culprits: seals. “We blame the seals on stealing our supplies,” he said.

Mr. Resler has a history with seals. During a 2019 dive in the area, a seal grabbed his left fin. “They do screw around with you,” he said. “I had one grab my left fin and almost yanked my left leg off, dadgummit. It scared the hell out of me.”

Louise Harrison, the Save the Sound New York natural areas coordinator, referred to the dives as an “amazing endeavor” and called Plum Island “a national treasure.”

Dr. Schlesinger said: “I think we have a great beginning for thinking about management strategies surrounding the island. If you ask scientists whether we should study more or research more, the answer is yes … There’s always something more to study, right? So, there’s no end to the quest for knowledge in the science and conservation world.”