Horseshoe crabs appeared in the fossil record approximately 450 million years ago. Almost unchanged they have lived through several ice ages, witnessed the rise and extinction of dinosaurs, and the evolution of mammals and plants. There are four living species of Horseshoe crabs, three reside in Southeast Asia and one in North America (Limulus Polyphemus). Despite surviving five mass extinction events, worldwide horseshoe crab numbers are dwindling.

Unfortunately, their decline can be directly traced to human exploitation. New developments on coastal waterways have impacted breeding grounds, higher demand for the species as bait food in commercial fisheries has led to overfishing. In Asia their roe is considered a delicacy, reducing the numbers of newborn crabs. Plus, their desirability in biomedical industry has all led to their growth instability.

Back to the question why are horseshoe crabs important? They are an indicator species. Their presence is an important part of coastal communities. During spawning a female horseshoe crab will lay a cluster of 4,000 tiny green eggs, she may lay several clusters in an evening. This abundance of eggs feeds fish, shore birds, turtles, sharks, conch as well as other marine life.

Additionally, the horseshoe crab is vital for the migration of shore birds, in particular the Red Knots. Red Knots follow a 9300-mile migration path from the artic in central Canada to Tierra del Fuego in Southern Argentina. Along the way they meet up with the Atlantic Horseshoe Crabs spawning in the Delaware Bay. By the time the Red Knots have reached the bay they have lost half their body mass and need to feast on the nutrient rich eggs of the horseshoe crab to continue their journey. Atlantic Horseshoe Crabs spawn when the water temperature reaches 60 degrees Fahrenheit. If the birds reach the bay before, or after the water reaches this optimal temperature then their ability to successfully finish their migration is hampered, further impacting this threatened species. The US Fish and Wildlife Service reported in the decades spanning the 1980’s and 2000’s seventy-five percent decline in red knots. In 2021 it is reported that the red Knots reached their lowest population.

Finally. according to NOAA, the horseshoe crab faces three threats due to climate change, ocean surface temperatures, ocean acidification and sea level rise. This not only impacts their survival, but also the various species which depend on their eggs. Fortunately, many organizations are studying the horseshoe crab and monitoring their numbers. Because of these efforts New Jersey has a moratorium on harvesting horseshoe crabs with the exemption of biomedical uses. However, is this enough protection and do the same moratoriums need to be in place along the entire coast?