GLOUCESTER, Mass. — HORSESHOE CRABS have been around for 475 million years, making them among earth’s oldest animals. They emerge from waters along the Eastern Seaboard during the high tides of full and new moons each May and June to spawn and lay their eggs on sandy beaches. The world’s largest population is concentrated in the Delaware Bay off the coasts of New Jersey and Delaware.
Arriving not far behind the crabs are thousands of small russet-colored shorebirds, known as red knots. They show up just in time to feast on the abundance of crab eggs before resuming their 9,300-mile journey from Tierra del Fuego to the Canadian Arctic. More than half of the red knots along the Western Atlantic flyway converge at this crucial springtime refueling stop, our own avian Serengeti.
But the number of horseshoe crabs has declined over the years. We’d been catching too many to use as bait to snag other sea creatures. That has meant trouble not only for red knots, whose numbers in the Delaware Bay have plummeted by 70 percent since the early 1980s, but for us.
Just as the red knots depend on crabs for food, we depend on them for their blood, which is exquisitely sensitive to bacterial toxins that can cause illness or death in humans. This has made a creature that survived the dinosaurs vital to modern medicine. The biomedical industry uses crab blood to create a clotting agent to test for bacterial contamination in an array of drugs and medical devices — from vaccines to intravenous medicines, heart stents and artificial hips.