Common name: Atlantic Horseshoe Crab

General Information

The Atlantic Horseshoe Crab (Limulus polyphemus) is a fascinating marine arthropod that has remained virtually unchanged for over 450 million years, earning it the title of a "living fossil." Despite its name, it is more closely related to spiders and scorpions than to true crabs. Its unique horseshoe-shaped carapace and long, spiked tail (telson) make it easily recognizable. These creatures are native to the Atlantic coast of North America, from Maine to the Gulf of Mexico.

Horseshoe crabs play a vital role in both marine ecosystems and human medicine. Their blue blood contains a substance called Limulus Amebocyte Lysate (LAL), which is used to detect bacterial endotoxins in medical applications. In the wild, their eggs are a crucial food source for migratory shorebirds, making them ecologically significant.

Care

Atlantic Horseshoe Crabs are not commonly kept in home aquariums due to their specific care requirements and large adult size. They require a spacious tank with a deep sandy substrate to burrow and forage. These crabs are sensitive to water quality and need stable salinity, temperature, and pH levels. They are best suited for public aquariums or experienced hobbyists with large marine setups.

Diet and Feeding

In the wild, Atlantic Horseshoe Crabs are scavengers and detritivores, feeding on organic matter, small invertebrates, and algae. In captivity, they can be fed a diet of sinking pellets, frozen foods like brine shrimp, and chopped seafood. It is essential to ensure they have access to food at the substrate level, as they are bottom-dwellers.

Behavior and Compatibility

Horseshoe crabs are peaceful and non-aggressive, making them compatible with a variety of other marine species. However, their burrowing behavior can disrupt delicate corals and aquascaping, so they are not considered reef-safe. They are also prone to accidentally overturning themselves, which can be fatal if not corrected promptly.

Reproduction

Breeding Atlantic Horseshoe Crabs in captivity is extremely challenging and rarely achieved. In the wild, they come ashore in large numbers during the spring to spawn on sandy beaches. Females lay thousands of eggs in shallow nests, which are fertilized externally by males. The larvae undergo several molts before reaching their adult form.

Symbiosis

Atlantic Horseshoe Crabs often host small symbiotic organisms like barnacles and flatworms on their carapace. These relationships are generally commensal, with the hitchhikers benefiting from a mobile home while the crab remains unaffected.

Health and Common Issues

Horseshoe crabs are hardy but require excellent water quality to thrive. Poor water conditions can lead to stress and health issues. They are also vulnerable to physical injuries, particularly to their delicate gills located under the carapace. Regular monitoring and maintaining a clean, stable environment are crucial for their well-being.

Habitat

Atlantic Horseshoe Crabs are found in shallow coastal waters, estuaries, and sandy or muddy substrates. They prefer areas with gentle currents and plenty of detritus to forage. Replicating these conditions in captivity is essential for their health and natural behavior.

Conservation Status

The Atlantic Horseshoe Crab is listed as "Vulnerable" by the IUCN due to habitat loss, overharvesting for bait and biomedical use, and declining populations. Conservation efforts include regulated harvesting and habitat restoration. Hobbyists are encouraged to avoid wild-caught specimens and support sustainable practices.