Limulus polyphemus

Conservation

Horseshoe crabs, Limulus polyphemus, are ecologically and commercially important.  They lay their eggs on sandy beaches in spring and summer, mainly during new and full moon cycles. Migrating shorebirds rely heavily on their eggs to supply energy required to complete their migration. Horseshoe crabs are also important to the medical industry. Biomedical companies catch horseshoe crabs for their blood, from which they produce Limulus Amebocyte Lysate (LAL).  LAL is used to detect contamination of injectable drugs and implantable devices; it is the most sensitive means available for detecting endotoxins, which are part of the outer membrane of the cell wall of certain bacteria, such as E. coli and Salmonella.  Finally, in some states horseshoe crabs are harvested commercially for bait to catch American eels, catfish, and whelk.

Horseshoe crabs are currently managed under Addendum VII of the Atlantic States Marine Fisheries Commission (ASMFC) Fishery Management Plan for Horseshoe Crab. A 2019 stock assessment evaluated the status of several regional populations, including the Delaware Bay region. High harvest levels during the 1990s led to rapid population declines in the mid-Atlantic region.  Management actions taken in 2004 and 2006 halted the population decline, and recent stock assessment results indicate the Delaware Bay population of horseshoe crabs appears to be recovering. New Jersey adopted a moratorium on the harvesting of horseshoe crabs in 2008.  Horseshoe crabs are a particularly important species in New Jersey because the Delaware Bay is the center of horseshoe crab spawning abundance on the Atlantic coast.

The New Jersey DEP Fish and Wildlife conducts many surveys that aid in gathering data to contribute to ASMFC’s stock assessments. The Delaware Bay Trawl and New Jersey Ocean Trawl Surveys conduct sampling throughout New Jersey’s coastal and bay waters. The trawls collect data on horseshoe crab abundance, as well as carapace length and sex data. The Delaware Bay Horseshoe Crab Spawning Survey is a collaborative study between New Jersey and Delaware. Each year, different organizations sample 24 beaches throughout Delaware Bay during peak spawning months to gather data on the numbers of males and females that are spawning on the beaches during the full and new moon lunar cycles. The data for the spawning survey is used to assist in establishing the M:F sex ratio for the stock assessments.

Given their life history, population growth will be slow and may be hindered by factors such as continued human use, habitat loss, food availability, illegal harvest, and incidental mortality; however, NJ DEP is taking steps, such as a harvest moratorium and beach replenishment, to protect this keystone species for the maximum benefit of all users.



More information about this species can be found below:

Description

• dome shaped shell
• brown to gray in color
• 12 legs under shell; 5 pairs for walking a set of tiny pinchers
• long spiky tail

Size

• 3.5 to 33 inches

Range

• Atlantic coast
• in and around shallow coastal marine and brackish water on soft, sandy, or muddy bottoms  

Facts

• females can lay between 60,000 and 120,000 eggs in batches of a few thousand at time
• closely related to spiders and scorpions, rather than crabs
• species has been living more than 400 million years
• moratorium on the harvest of horseshoe crabs within the state
• diet consists of marine worms, clams, mussels, crustaceans, and slugs
• largest concentration of breeding horseshoe crabs is found along the Delaware Bay
• 9 eyes in total with various light receptors