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Go DeeperSidebar: Delaware's Dinosaur Delaware Bayshores
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Lifesaver
Throughout most of the past century, the horseshoe crab never registered as much more than an oddity for beach goers to step around. From the mid-1800s to the 1950s, a few outfits collected horseshoes on beaches or in nets, dried them and ground them into a nitrogen-rich fertilizer for crops. “My grandparents fed them to their chickens and their hogs; it was the only thing they were good for,” says Bill Hall, a marine researcher and education specialist at the University of Delaware.
Then, in the 1950s, scientists discovered a compound in the crab’s copper-based blood that clots when it comes into contact with harmful bacteria. Many countries, including the United States, now require that the biomedical industry use this compound, called lysate, to test just about any object or substance used during a medical procedure that could cause infection—syringes, scalpels, intravenous drugs.
“Most people have no idea,” says Hall. “They put the horseshoe crab right up there with the mosquito in terms of its value to people.” But thanks to lysate’s ability to alert against infection, the horseshoe crab has helped save many lives—more than a million people, according to one estimate—since the compound was discovered.
To supply the biomedical industry with this anti-infection compound, however, approximately 300,000 crabs are caught and bled each year. While some of these crabs are returned to the ocean, only a little worse for the wear, as much as 40 percent of the catch dies from the trauma or is sold to the bait industry. Bill Hall helped start the crab count in 1990 in part to monitor the impact of the biomedical industry, which had—and still has—a huge stake in sustainably managing the horseshoe harvest. “This crab saves lives,” says Hall. “There is nothing to replace it.”
While the biomedical industry’s limited catch was not considered a major threat to the horseshoe crab population, in the mid-1990s Hall and others began to notice signs that something was going wrong with the numbers of crabs coming onto shore during the annual spawning counts.
Half a world away, a culinary trend was sending the Delaware Bay horseshoe crab population into a downward spiral. Beginning in the 1990s, surging demand in Asia for whelk (or conch, as it is called) and American eel gave watermen along the Atlantic Coast a big incentive to catch horseshoe crabs, which they slice up and use as bait in traps. Suddenly, a single horseshoe could fetch more than a dollar, and fishermen were scooping them up by the millions each year. From the late 1960s to 1996, the annual catch increased from 10 tons to 2,550 tons.
A crash in the horseshoe population wasn’t far behind. And as the crab population declined, it put at risk dozens of other species, including threatened loggerhead sea turtles (one of the few predators large enough to consume adult horseshoes) and at least 11 species of migratory birds, which rely on the crab’s protein-packed eggs as a crucial food source during their intercontinental spring migrations.
The rufa subspecies of the red knot, a shorebird famous for its 9,000-mile migration from the tip of South America to the Canadian Arctic, was hit especially hard. The number of these red knots stopping over in the Delaware Bay dropped from 90,000 in 1989 to 13,000 in 2006. “They have declined to the point of being candidates for the endangered species list,” says Dave Smith, a biological statistician with the U.S. Geological Survey.
But the horseshoe crab isn’t important just for the support it provides birds and marine animals, says Bill Hall. They are “a model of why we should be concerned about biodiversity,” he says. “The crab has a lot of implications for our lives.”
Nature picture credits: Photos © Christian Ziegler
