Species Fact Profile: Atlantic Horseshoe Crab (Limulus polyphemus)

Atlantic Horseshoe Crab 

Limulus polyphemus (Linnaeus, 1758)

Range: Atlantic Coast of North America, southern Canada to the Yucatan Peninsula

Habitat: Shallow Coastal Waters with Mud or Sand Bottoms

Diet: Small Marine Invertebrates, Algae

Social Grouping: Vast breeding congregations

Reproduction: Breed at night in the springtime (exact time varies by season), with sometimes thousands of crabs gathering on the beach.  Several males surround each female as she lays her eggs (about 20,000 per night, in clumps of 5,000, may lay up to 100,000 per season), fertilizing them externally.  The fertilized eggs hatch after two weeks.  The young are mature at about 10 years of age.

Lifespan: Estimated 20-40 Years

Conservation Status: IUCN Vulnerable

• Body length up to 60 centimeters (including the tail) and weigh up to 4.8 kilograms, with females being a quarter to a third larger than the males.  The largest horseshoe crabs are found in the central portion of the range, with the extreme northern and southern crabs being smaller
• Front portion of the body is covered with a smooth, dome-like carapace, green, grey, or brown in color, roughly resembling a horseshoe in size.  The shell is molted as the crab grows.  The crab has ten legs growing from under the shell, with the mouth located in the center
• Body is divided into three segments - a head (containing most of the vital organs), the opisthosoma (middle), which contains the gills and ridges used in movement, and the tail.  The long, pointed tail resembles that of a stingray, but is actually harmless; the crabs use them for steering, as well as for righting themselves if they are overturned.
• Primarily moves by walking along the bottom of the sea, but can swim on its back if needed
• This species dates back at least 450 million years, predating the dinosaurs by 200 million years.  Despite their name, they are more closely related to arachnids (spiders and scorpions) than to crabs, but are part of a separate order
• Their eggs are a very important food source for migrating shorebirds.  Adults and juveniles may be predated by fish and sea turtles
• Latin name translation: Limulus means "askew," while "polyphemus" was the name of a one-eyed giant (cyclops) in Greek myth.  This species is believed by some to have only one eye, but actually has ten
• The species has been documented in the Pacific coast of the US, as well as Africa, Europe, and Israel, but these are believed to have been released by humans.  Efforts to introduce the species to other locations for future harvesting have not proven successful
• Horseshoe crabs are used in biomedical research because of the properties of their blood.  Lysate, found in the blood, clots in response to bacterial toxins, and has been used for a variety of scientific purposes, including vaccine development.  Efforts are underway to develop a synthetic version which will reduce the need for live crabs to be harvested.  Blood harvesting does not kill the crabs, which may be released into the wild after being drawn, but the process may reduce their chances of reproductive success
• Horseshoe crabs are most threatened by over-harvesting for human use, as well as loss of suitable habitat due to development.  Climate change also reduces the availability of their preferred nesting sites.