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American Horseshoe Crab

Horseshoe crabs are often called “living fossils,” as they have existed for more than 450 million years—long before dinosaurs appeared. Despite their name, they are not true crabs but are more closely related to spiders and scorpions.

 

The American horseshoe crab has a hard, rounded shell shaped like a horseshoe and a long, pointed tail spine (called a telson), which helps it flip back over if it is overturned. In order to grow, young horseshoe crabs will shed their shell multiple times a year until they reach adulthood, which takes about nine or ten years. Adults typically measure around 60 centimeters (24 inches) in length, including the tail, and weigh up to 4.8 kilograms (11 pounds).

American horseshoe crabs are the only horseshoe crab species found in North America, found along the Atlantic coast of North America from the Yucatán Peninsula to the Gulf of Maine. As adults, they are typically found in shallow waters walking along the ocean floor with their five pairs of legs. Mussels and clams are their most common prey, although they will feed on almost anything – including worms, algae, and fish! One of the most remarkable behaviors of horseshoe crabs occurs during spring and summer when thousands may come ashore to spawn. Females lay hundreds of thousands of greenish eggs in the sand, which become an important seasonal food source for shorebirds.

 

 

American horseshoe crabs face multiple threats, which has led to them being considered Vulnerable to extinction by the IUCN Red List.

Overharvesting 

Horseshoe crabs are collected both for bait in eel and conch fisheries18 and for biomedical purposes, as their unique blue blood contains a compound used for detecting bacterial contamination in medical products. However, regulations have been put in place to prevent overharvesting, which seem to be having a positive impact for horseshoe crab populations across most of their range.

Habitat Loss 

The greatest long-term threat to horseshoe crabs is believed to be habitat loss. Coastal development, beach erosion, and climate change also threaten their spawning grounds, reducing the availability of sandy beaches needed for egg-laying.

 

 

Active management and an emphasis on sustainable harvest is crucial to prevent horseshoe crab populations from continuing to decline.  Science-based management plans like these can help these animals and others rebound and lead to healthy, abundant oceans. Oceana campaigns around the world to increase the number of fisheries with management plans and catch limits. We also work to protect ocean habitats that are crucial to the survival of species like horseshoe crabs.

 

 

Animal Diversity Web 

Florida Fish and Wildlife Conservation Commission 

IUCN Red List 

Langer, M. C., Ezcurra, M. D., Bittencourt, J. S., & Novas, F. E. (2010). The origin and early evolution of dinosaurs. Biological Reviews, 85(1), 55-110. https://doi.org/10.1111/j.1469-185X.2009.00094.x 

NOAA: Are horseshoe crabs really crabs? 

U.S. Fish & Wildlife Service: Atlantic Horseshoe Crab 

Walls, E. A., Berkson, J., & Smith, S. A. (2002). The Horseshoe Crab, Limulus polyphemus: 200 Million Years of Existence, 100 Years of Study. Reviews in Fisheries Science, 10(1), 39-73.  

 

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