Its blue blood is harvested for medical researchers and used by drug and medical device makers to test for dangerous impurities in vaccines, prosthetics and intravenous drugs.
The crabs are used by fishing crews as bait to catch eels and sea snails. And their eggs are a critical food source for a declining subspecies of bird called the red knot – a rust-coloured, migratory shorebird listed as threatened under the Endangered Species Act.
The competing interests have set up a clash among researchers, fishing crews and environmentalists over new protections designed to keep more of the crabs in the environment.
In medical research, the animals are drained of some of their blood and returned to the shore, but many die from the bleeding. And a drive to create synthetic alternatives has yet to succeed in phasing out the crabs from use.
The harvest of horseshoe crabs has emerged as a critical issue for conservationists in recent years because of the red knot.
The birds – which migrate some 30,577km (19,000 miles) round trip from South America to Canada, and must stop to eat along the way – need stronger protection of horseshoe crabs to survive, said Bethany Kraft, senior director for coastal conservation at the Audubon Society.
Kraft and other wildlife advocates said the fact that the guidelines for handling crabs are voluntary, and not mandatory, leaves the red knot at risk.
“Making sure there is enough to fuel these birds on this massive, insanely long flight is just critical,” Kraft said. “There’s very clear linkage between horseshoe crabs and the survival of the red knot in the coming decades.”
The horseshoe crabs have been harvested for use as bait and medicine from Florida to Maine over the years, though the largest harvests are in Maryland, Delaware, Massachusetts and Virginia. According to US federal fishery statistics, the crabs were worth about $1.1m in total at the docks in 2021.
That figure is dwarfed by seafood species such as lobsters and scallops, which are routinely worth hundreds of millions of dollars. However, horseshoe crab fishers are dedicated stewards of a fishery that supplies a vital product, said George Topping, a Maryland fisherman.
“Everything you do in life comes from horseshoe crab blood. Vaccines, antibiotics,” he said. “The horseshoe crab stocks are healthy.”