Volunteers become environmental stewards as they help marine scientists tag, study horseshoe crabs

Under a nearly full moon, beams from headlamps illuminating the shoreline, seven volunteers recently set out on a late-night task to count and tag horseshoe crabs in the Peconic Bay in Southold.

High tides during full and new moon cycles in May and June mark the spawning season for the prehistoric animals, which scientists estimate have been around for about 445 million years.

"You're almost putting a message in a bottle when you tag them," said Catie Callaghan, 40, of Jamesport, who coordinates the tagging effort at South Harbor Road beach in Southold.

The beach is one of nearly 30 sites monitored between Staten Island and Fishers Island in a joint effort between Cornell Cooperative Extension of Suffolk County and the state Department of Environmental Conservation. The program unites marine biologists with volunteers eager to help conservationists track spawning, migration and survival patterns in the species and has helped bolster citizen science throughout the region. 

"I would have never gone near one — let alone pick one up," Callaghan said, reflecting on her first time volunteering with her daughter's Girl Scout troop eight years ago. Once fearful of horseshoe crabs due to their intimidating appearance, Callaghan now recruits a cadre of friends, co-workers and even strangers to help comb the beach at night.

"It's a way to go out in the community, do a beach walk at night and do this oddball thing," she said. "Now, [volunteers] are people I would have never met otherwise. That's the neatest thing about it."

After surveying the conditions, Callaghan teaches the group how to properly measure their shells and use an awl to attach a white disc that's used to report future sightings.

The data provides the cooperative and DEC crucial insight into the species amid a population decline attributed in part to harvesting the species for whelk and eel bait, which is limited in New York State to 150,000 crabs per year. In other areas of the Atlantic, horseshoe crabs are harvested for biomedical research, as their blue blood helps test for vaccine viability.

Horseshoe crabs munch on small mollusks and worms and their eggs provide a food source for migrating shorebirds like red knots and ruddy turnstones.

“I think of horseshoe crabs as mini marine tractors,” said Pete Topping, executive director of Peconic Baykeeper, a nonprofit focused on water quality. “They’re keeping the bay bottom productive.”

Topping co-manages a site on Southampton’s Meadow Lane with Sally Kellogg, who leads marine programs at the South Shore Estuary Reserve. 

Before tagging begins, volunteers count how many horseshoe crabs are active that night. On a peak night in May, Topping said his group spotted more than 2,000 in the shallow waters of Shinnecock Bay.

Data from the DEC shows that spawning activity increased at 17 of 25 sites monitored in 2022.  Last year, volunteers tagged 5,044 horseshoe crabs, according to the DEC.

Matt Sclafani, a marine educator at Cornell Cooperative Extension of Suffolk County, estimates that between 500 and 600 people volunteer each season, becoming environmental stewards along the way. “They’re sharing that information with the public to gain appreciation of a non-glamorous species that’s really important to the ecosystem,” he said. 

One of the volunteers is Ben Gonzalez, 52, an oyster farmer from Shelter Island, who was struck with childlike awe as he placed his first tag.

“I work in aquaculture, so I know how interesting shellfish can be — even though they look boring,” he said. “But this is impressive. Nature is amazing.”