Horseshoe Crabs Are an Essential Part of Life in Delaware

Photographs by Ariane Müller

Delaware is honored to have the world’s largest population of spawning horseshoe crabs—but for how long?

In June, many flip hamburgers at picnics. In Delaware, we also flip horseshoe crabs on beaches. Either could involve beer, but this is serious ecology and business, too.

The Delaware Bay has the world’s largest spawning population of horseshoe crabs, where tens of thousands crawl from the water in an ancient survival mating ritual. It happens during full- and new-moons high tides on beaches like Slaughter, Pickering and Kitts Hummock.

Females dig holes in the sand. Males fertilize their eggs, which in two weeks hatch as larvae. If all goes well, the budding offspring return to the ocean floor for a decade until they, as adults, come ashore in a 450 million-year ongoing spectacle of nature.

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horseshoe crabs on the beach

In the First State, we treasure the horseshoe crab, our official state marine animal since 2002, when then–Cape Henlopen High student and Sussex County Science Fair winner Abigail Bradley petitioned politicians to honor it as such.

But there’s more to the conservation of horseshoe crabs, which are among the world’s 10 oldest surviving creatures. They save lives.

For decades, these arthropods have been harvested and bled for their copper-based, baby-blue blood. The miracle substance is used to test injectable drugs and implanted medical devices for cleanliness and contamination by helping detect endotoxins. Their blood contains Limulus amebocyte lysate (LAL), which instantly thickens when contaminated. In the biomedical industry, it helps purify surgical implants, IV fluid lines and much more. A horseshoe crab’s own LAL initiates healing when their shells crack or they’re otherwise injured.

To obtain this precious resource, over 600,000 horseshoe crabs a year are drained of blood for about eight minutes per session, sometimes longer. According to industry reports, around 30% of the crabs die during the blood-draining process, although reports from independent researchers indicate that this may be a vast underestimation. Their data suggests the mortality rates may be twice as high. This has prompted resistance from animal and environmental rights activists, as well as rules for harvesting.

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horseshoe crabs on beach

In the bay’s ecosystem, horseshoe crabs are known as a keystone species, meaning they play a large role in the survival of the rest of the species around them in a way that can’t be replicated. Horseshoe crab eggs are an important food source for other marine animals as well as shorebirds like the federally listed threatened red knot.

Though Delaware’s shores are ideal for spawning, the state remains detached from the important horseshoe crab–related biomedical industry, according to Michael Globetti of the Delaware Department of Natural Resources and Environmental Control. “None that mate on Delaware’s side of the bay knowingly end up in that industry,” he says.

Because endotoxins are deadly, even in nanogram amounts in your bloodstream, ruling them out is FDA-mandated. The use of a bacterial endotoxin test (BET), via LAL has become a global market, but just four U.S. companies harvest horseshoe crab blood and produce the test. Two, Lonza (Walkersville, Maryland) and the Associates of Cape Cod (East Falmouth, Massachusetts), also have an alternative FDA-approved, animal-free BET. There’s also Charles River Laboratories (Charlestown) and FUJIFILM Wako Chemicals U.S.A., headquartered on the Eastern Shore of Virginia. A fifth, Limulus Labs (Cape May), is a collection facility that harvests on the other side of the Delaware Bay.

“We don’t need it, and I’m glad we don’t have it,” says Glenn Gauvry, founder and president of the Ecological Research and Development Group (ERDG), the first horseshoe crab conservation organization to promote an animal-free BET and to team with Lonza, which had the first patent to produce an alternative. “It would please the hell out of me if no one harvested. At the end of the day, we need to get the most amount of people to love and protect these animals.”

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crabs in ocean
Horseshoe crabs are arachnids, related to spiders and scorpions. These prehistoric creatures have been around for over 450 million years. Their unique blue blood contains a precious resource, LAL, which detects endotoxins and can be used to keep medical equipment, tools and implants sterile.

The primary focus of his internationally recognized nonprofit in Little Creek (where he was a five-term mayor) is the conservation of the world’s four horseshoe crab species—not only the East Coast’s Limulus polyphemus.

“It’s a hard sell, but it’s getting easier,” says Gauvry, who started ERDG in 1995. “The approach we take is to thread the needle between interest groups, but we’re the only ones in it for horseshoe crabs, and not what the horseshoe crabs will do for something else. First and foremost, we’re trying to conserve the species.”

Gauvry saw his first horseshoe crab in 1969 while stationed at the Dover Air Force Base, then again as a member of the Tri-State Bird Rescue and Research, oil spill response team. In the late 1980s and early 1990s, the nonprofit was trying to determine how to protect the Delaware Bay ecology if there was an oil spill there.

That ecology is perfect for horseshoe crabs, which are both terrestrial and aquatic since they come ashore in protected areas to spawn and lay eggs, then depend on the bay’s shallow waters as nurseries. “We’re on the sweet spot,” Gauvry says.

The number of horseshoe crabs in the Delaware Bay exceeds 40 million—about 31 million adults—because of the care taken for them, explains Maryland-based microbiologist Allen Burgenson, an LAL scientist who also serves on the advisory panel of the Atlantic States Marine Fisheries Commission. He’s been involved in horseshoe crab ecology for 60 years and with endotoxin testing for 40. During spawning, he helps flip over upside-down crabs on Delaware beaches. Like New Jersey, our state has a moratorium on the commercial harvest of female horseshoe crabs as bait for the fishing industry.

horseshoe crab blood
A row of horseshoe crabs undergoing blood harvesting. Many crabs do not survive this process, which has drawn criticism from environmental activists. An even bigger problem facing the horseshoe crab population is overfishing for bait.

The largest amount of crab-killing comes at the hands of the fishing industry. “The biggest fraction is for bait to catch eel and whelk,” says Steve Cottrell, president of the Delaware Audubon Society. “They’re basically treating horseshoe crabs like trash. …You can use waste parts from chicken and cat food [instead]. But horseshoe crabs are a little easier and cheaper for them. So, they’re putting a whole bunch of species of wildlife at risk,” Cottrell points out.

Among interventions, in 1998 ERDG started the program Just Flip ’Em!, which states, “When you see a horseshoe crab that is stranded upside down on the beach, just flip [it] over.”

The logo is posted on several beaches along the Atlantic Coast, along with a bar code to scan and learn more, and has attracted eager tourists. “People come from all over to help with their care,” Gauvry points out.

A year later, its Backyard Stewardship Initiative, which enrolls coastal communities in education and conservation efforts, launched its first horseshoe crab sanctuary at Broadkill Beach.

“The horseshoe crabs go where they can spawn, and in the Delaware Bay that’s usually someone’s backyard,” Gauvry says. Seven more followed: Pickering Beach, Kitts Hummock, Slaughter Beach, Prime Hook National Wildlife Refuge (Fowler Beach), Prime Hook Beach, Camp Arrowhead (Rehoboth Bay) and Big Stone Beach are all now designated sanctuaries.

“The question is, ‘Would we care about the horseshoe crab if it didn’t provide a surplus of eggs for the migratory birds to feed on, give its body to be butchered and used as bait in conch and eel fisheries, or its blood for the production of a bacterial endotoxin test?’” Gauvry asks. “There was a time when the answer would’ve been ‘no.’”

Now, with its broad-based pharmaceutical, biotech and healthcare influence, Delaware should become the first state to incentivize the use of alternative animal-free BET instead of continuing to use LAL, he urges. “It would make a profound difference in the conservation of the species.”

The Great Migration

Arctic shorebirds and Atlantic marine animals rely on the horseshoe crab for survival.

Every spring, when horseshoe crabs swarm our shores to mate and lay their eggs, several Arctic-nesting shorebirds, including sandpipers and ruddy turnstones, are also migrating.

Another of these shorebirds is the critically endangered red knot, a 9-inch copper-breasted powerhouse that undertakes one of the longest migrations of any bird, spanning over 9,000 miles. They fly from the southern tip of South America and make only two or three stops before they reach their Canadian Arctic breeding grounds.

“Obviously they lose a lot of weight during their flight, and when they stop, they refuel,” explains Delaware Audubon Society president Steve Cottrell. “Historically, their biggest stopover was in the Delaware Bay.” Here they feast on the recently laid horseshoe crab eggs, rich in nutrients and fat.

However, due to overharvesting of horseshoe crabs for bait and medical bleeding, as well as mortality due to bycatch and habitat loss brought on by climate change, their population has decreased by 60% over the last quarter of a century, according to the Horseshoe Crab Recovery Coalition website. Recent studies have also shown a steep drop in the number of female horseshoe crabs, which means fewer eggs, and subsequently fewer shorebirds.

Horseshoe crab eggs are also a food source for several varieties of fish. “Those smaller fish are prey for larger fish. So, if you collapse the source, the higher levels of the food chain collapse as well,” Cottrell points out. Horseshoe crabs are key to the survival of their ecosystem.

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