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Predating the dinosaurs and surviving more than 450 million years, the Atlantic horseshoe crab is now facing steep population decline in Long Island Sound — largely due to human activity.
New research from The Maritime Aquarium analyzed six long-term data sets covering up to 46 years of trends in the sound. Scientists found that populations of Atlantic horseshoe crabs have dropped by 2 to 9 percent annually in each sample.
The findings, published in Scientific Reports and The Biological Bulletin, warn of the risk of local extinction without immediate, coordinated action.
“This research exemplifies The Maritime Aquarium’s commitment to science-driven conservation and regional leadership in protecting Long Island Sound,” said Jason Patlis, the aquarium’s president and CEO. “It also underscores the need for more action to protect this important species.”
Why it matters
Horseshoe crabs come ashore each spring and summer to spawn, laying eggs that provide vital food for birds, turtles, and fish.
For the rest of the year, they live on the bottom of the sound, stirring up nutrients that feed countless other species.
“They’re important to protect because they really serve as a vital food web for multiple endangered species, different fish, turtles, and thousands of migratory shorebirds as well,” said Rebha Raviraj, a co-author of the studies and project manager at the aquarium’s conservation department. “They serve as a keystone species. Without them, there would be cascading consequences for the rest of the ecosystem.”
The threats
The studies cite several major pressures on horseshoe crabs: overharvest and bycatch, coastal habitat loss, insufficient management, and climate change.
One solution, Raviraj said, is to protect and restore spawning beaches and juvenile habitats. Captive breeding and “headstart” programs — where crabs are raised and released into the wild — could also help boost numbers.
Researchers also urged the biomedical industry to reduce its reliance on horseshoe crab blood, long valued for its unique compounds that test medical equipment for toxins.
“It’s been very useful in the biomedical industry for many years now, but at the detriment of the species,” Raviraj said.
Calls for protection
Despite their intimidating look — with a hard shell, long tail, and spindly underbelly — horseshoe crabs are harmless. Raviraj advised beachgoers to give them space and, if they find one flipped on its back, gently turn it over to improve its chances of survival.
Connecticut banned both commercial and hand harvesting of horseshoe crabs and their eggs in 2023. New York passed similar legislation last year, the Horseshoe Crab Protection Act, but it has yet to be signed into law.
“We recommend the urgent protection of the species at the state level, but we also recommend that horseshoe crabs become listed under the U.S. Endangered Species Act,” Raviraj said.
Next, researchers plan to survey beaches in Connecticut to study egg presence and identify the most successful breeding areas.
The aquarium is also active in Project Limulus, a tagging and tracking program that helps scientists monitor populations and educates the public about the species’ importance to both ecosystem and human health.
Top: Researcher Rebha Raviraj holding an Atlantic horseshoe crab. (Credit: Kristen Cuppek)
