Celebrating the American Horseshoe Crab: Long Island Sound’s Living Fossil

In early summer, beachgoers and residents in Connecticut and New York might encounter a spiky, spider-like creature crawling up the shore. The American horseshoe crab, Limulus polyphemus, is an ancient creature that has existed since before the dinosaurs and has survived five mass extinction events. Despite their intimidating appearance, the American horseshoe crab is harmless and plays a crucial role in both human and environmental health. In 2020, the IUCN SSC Horseshoe Crab Specialist Group designated June 20 as International Horseshoe Crab Day.

To increase public awareness and improve data-gathering efforts for the species, Project Limulus was formed in 1998 by the late Dr. Jennifer Mattei, a professor of biology at Sacred Heart University.

All About the Crabs

A woman in sunglasses and a white t-shirt holds up a horseshoe crab and smiles.
Kasinak poses with a horseshoe crab. Photo courtesy of Jo-Marie Kasinak.

Horseshoe crabs have remained nearly unchanged for roughly 445 million years and can be spotted frequenting the Atlantic and Gulf coasts from Nova Scotia to as far south as Mexico. A special protein in their blood, Limulus Amebocyte Lysate (LAL), can be used to detect bacterial endotoxins. In their presence, LAL will clot, making it easy for medical professionals to detect presence and contamination.

“In addition to their connections to human health, they have a strong connection to the local ecosystem, said Jo-Marie Kasinak, the program’s new director and former outreach coordinator. “In areas where you don’t have as many horseshoe crabs, you have a decrease in biodiversity in communities that are associated with them.”

In the Long Island Sound region, Project Limulus has reported almost no shorebirds eating horseshoe crab eggs, due to a lack of access to the eggs. Horseshoe crabs bury their nests in the sand and population density can lead to horseshoe crabs digging up other crab nests during spawning events, exposing eggs on the beach’s surface. The more abundant the species is, the more involved they can become in the local food web.

“We don’t have that kind of density,” said Kasinak. “The only bird or anything we’ve seen eating the eggs is a Canada goose. It sits on the nest and stirs up the sand with its feet.”

Overfishing, habitat loss, and warming waters due to climate change have decreased their numbers in Long Island Sound since the ‘90s. State resource managers, however, are looking to reverse this trend. In 2023, Connecticut passed a statewide ban on harvesting horseshoe crabs which went into effect in October. New York followed not far behind, passing a bill that would ban harvesting in the state’s legislature in early June of this year.

An American horseshoe crab tagged with a white circular button that includes a Fish and Wildlife Service url.
A look up close at a tagged crab. Photo courtesy of Jo-Marie Kasinak.

“I am glad to see these bans have come through because now we can give the crabs a chance to recover,” said Kasinak. “If we are seeing more adults able to breed successfully without being disturbed, we should also be able to find more babies.”

Project Limulus assesses shell condition and thickness to estimate age groups, from one to three, with one representing newly molted adults that have freshly entered the sexually mature pool. An increase in this population is expected, along with more sightings of juvenile crabs.

A Conservation Flagship Tool

Project Limulus held outreach events throughout May and June across Connecticut, with tagging led by students. Graham Templeman, a graduate student at Southern Connecticut State University, returned for his third year spreading the word about horseshoe crabs. Templeman, who majored in biology as an undergraduate at SHU, had initially pursued a physical therapy track. A required ecology course with Mattei altered the trajectory of his career and Project Limulus is now an important part of his thesis, which explores how to statistically measure the concept of ocean identity.

Pioneered by a group of researchers including Kasinak and Mattei, ocean identity (OI) is defined as the cognitive, emotional, and behavioral connections people have to ocean spaces. Project Limulus is being used as a pilot case study to role out the new survey. Researchers hypothesize that those who attend outreach programs through the program will have a higher ocean identity.

A man in a white t-shirt and hat crouches down, holding a notepad and pen.
Templeman speaks with a tagging volunteer at Milford Point, Connecticut.

“The cool part of Project Limulus is it’s all volunteer-based,” said Templeman. “We’re not forcing anyone to come out to these programs. For me, that’s really the best part. You have so many people who are eager and have a strong desire to learn more.”

Although horseshoe crabs are considered by some to be not particularly charismatic megafauna, Project Limulus researchers see them as an important species for getting people to care about other areas of maintaining a healthy ecosystem in and around Long Island Sound.

“People always tell me horseshoe crabs are creepy and alien-like. Yes, they look a little weird, but they don’t hurt you and the strangeness about them is a draw to me,” said Templeman. “These guys are really cool, they look different from most species, in addition to the fact that they are ancient. They are super resilient.”

Please complete your newsletter signup.