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Atlantic horseshoe crabs look like tiny battle tanks roving in the seas and on the shores of the Atlantic and Gulf Coasts of North and Central America.
They are covered by a hard, dome-shaped shell that protects their bodies. Despite its name, this animal is not a true crab and is more closely related to spiders and scorpions. Horseshoe crabs have existed for more than 400 million years.
Each spring, they come ashore in mass spawning events to lay millions of eggs on sandy beaches. These densely aggregated eggs are a crucial food source for migrating shorebirds, especially red knots, providing the energy needed to complete their long-distance migrations.
Why are horseshoe crabs imperiled?
Though they are a resilient species, horseshoe crab population numbers are either dwindling or being maintained at impoverished levels, which is concerning for the fish, reptiles and birds that rely on horseshoe crab eggs and adult crabs alike for food.
Horseshoe crabs have unique, copper-based, bright blue blood that clots when exposed to bacteria and is used in the biomedical industry to detect contamination in drugs and medical devices. Over harvesting for medical testing has led to the species’ significant decline. Roughly 700,000 horseshoe crabs are taken from beaches during the spawning season and forcibly bled to obtain their blue blood for biomedical purposes. Though survivors are returned to the sea, up to 30% of bled crabs can die.
Climate change alters the coastal beaches and shallow waters horseshoe crabs need to spawn, posing a growing risk to this animal. Sea-level rise and stronger storms can erode or narrow spawning beaches. Changes in water temperature and timing can disrupt when and where crabs come ashore.
Habitat loss, including coastal development, shoreline erosion due to climate change and beach armoring, as well as overharvesting are the greatest threats to Atlantic horseshoe crabs.
Defenders' Impact
Defenders is a member of the Horseshoe Crab Recovery Coalition, an alliance of national, state and local organizations working to recover horseshoe crab populations by 2030.
Defenders is actively pursuing the protection of key spawning habitats, such as those within the National Wildlife Refuge System. We successfully litigated over the illicit harvesting of horseshoe crabs from Cape Romain National Wildlife Refuge, near Charleston, South Carolina, as well as unsustainable harvesting on other beaches across South Carolina. Defenders is advocating to maintain a moratorium on harvesting female horseshoe crabs in the Atlantic states. We are also advocating for the widespread adoption of the synthetic alternative to horseshoe crab blood, which would spare millions of crabs from the bleeding process.
What You Can Do
Flip overturned horseshoe crabs that you find on the beach by gently grabbing its hard outer shell. Never pull or lift the crab by its tail.
Support coastal restoration efforts. Obey all posted signs on beaches. Keep trash off the beaches and out of the ocean.
About
There are four species of horseshoe crabs, three of which live along the coasts of Southeast and East Asia. Atlantic horseshoe crabs spawn along the East and Gulf Coasts of North America.
Horseshoe crabs can be found in sandy mud flats and shallow brackish waters, but they also feed in deeper waters offshore.
Horseshoe crabs go through 16 or 17 molts during their development and reach adulthood at 10 years. Most often, horseshoe crabs crawl along the ocean floor, but they can, and do, swim and use their telsons, or tails, as rudders.
Horseshoe crabs move from the open ocean to the coasts at night to breed during full moons and high tides. Females release pheromones to attract the males when it is time to mate and dig small nests to deposit their eggs. Males then fertilize the eggs. Atlantic horseshoe crabs’ mass spawning events, where females lay millions of eggs, occur in the spring.
Horseshoe crabs eat worms, clams and other mollusks, some fish and algae along the ocean floor.
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