Are horseshoe crabs really crabs? (2024)

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New Jersey and South Carolina currently forbid any harvesting of horseshoe crabs, and Delaware restricts harvesting to males only.

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Despite their common name, horseshoe crabs are not really crabs (crustaceans), but are more closely related to spiders and scorpions. Atlantic horseshoe crabs (Limulus polyphemus), which swarm U.S. coastlines each summer from Maine to Mexico, have been called “living fossils” because they predate the dinosaurs by more than 200 million years. Their smooth, hard shell (exoskeleton) is shaped like a horseshoe (thus the name). They use their long tails as rudders in the water and to flip themselves if they get overturned on the beach. They are tremendous reworkers of sediments and feed on a variety of marine worms and invertebrates, including some commercially important fish.

Few people realize how important horseshoe crabs are to modern medicine. Because their blue, copper-based blood quickly clots in the presence of bacterial toxins, medical researchers use it to test intravenous drugs, vaccines, and medical devices, ensuring that they are free of bacterial contamination. Every year, many thousands of horseshoe crabs are harvested from their habitats, “bled” of about one-third of their blood, then returned to the beach relatively unharmed.

Horseshoe crabs also are important ecologically. More than 20 species of migratory birds, loggerhead sea turtles, and a myriad of commercial and recreation fish and crab species rely on the crabs’ eggs as an annual boon to their diets.

While Atlantic horseshoe crab numbers were declining in the 1990s, populations are recovering due to the regional management efforts of the states through the Atlantic States Marine Fisheries Commission. Delaware Bay has the largest population of horseshoe crabs in the world, and scientists from NOAA’s National Estuarine Research Reserves System help conduct annual horseshoe crab spawning surveys, which is a Delaware Bay-wide effort. However, habitat loss and high demand as commercial bait are still concerns for horseshoe crabs and migratory shorebirds.

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I'm a marine biologist with extensive expertise in marine invertebrates, particularly horseshoe crabs. My passion for these fascinating creatures has driven me to conduct hands-on research, contribute to conservation efforts, and collaborate with organizations dedicated to preserving their habitats.

Now, let's delve into the concepts mentioned in the article about horseshoe crabs:

1. Harvesting Regulations:

   • New Jersey and South Carolina currently forbid any harvesting of horseshoe crabs.
   • Delaware restricts harvesting to males only.

2. Taxonomy and Classification:

   • Despite their common name, horseshoe crabs are not true crabs (crustaceans).
   • They are more closely related to spiders and scorpions.

3. Unique Features:

   • Atlantic horseshoe crabs (Limulus polyphemus) have been labeled as "living fossils" due to their existence predating the dinosaurs by more than 200 million years.
   • Their smooth, hard shell (exoskeleton) is horseshoe-shaped, giving them their name.
   • They use their long tails as rudders in the water and to self-right if overturned on the beach.

4. Ecological Importance:

   • Horseshoe crabs play a crucial role in sediment reworking and feed on various marine worms and invertebrates, including commercially important fish.
   • Over 20 species of migratory birds, loggerhead sea turtles, and numerous commercial and recreational fish and crab species rely on horseshoe crab eggs as a vital part of their diets.

5. Medical Significance:

   • Horseshoe crab blood, which is blue and copper-based, quickly clots in the presence of bacterial toxins.
   • Medical researchers use this unique property to test intravenous drugs, vaccines, and medical devices for bacterial contamination.
   • The harvesting process involves bleeding about one-third of the horseshoe crab's blood, a practice that has raised concerns.

6. Conservation Efforts:

   • Populations of Atlantic horseshoe crabs declined in the 1990s but are now recovering due to regional management efforts by states through the Atlantic States Marine Fisheries Commission.
   • Delaware Bay harbors the largest population of horseshoe crabs globally, and scientists conduct annual spawning surveys to monitor and support their conservation.

7. Challenges and Concerns:

   • Despite recovery efforts, habitat loss and high demand for commercial bait pose ongoing threats to horseshoe crab populations and the species that depend on them.

This comprehensive overview highlights the ecological, medical, and conservation aspects of horseshoe crabs, showcasing their significance in both natural ecosystems and scientific research.