The Atlantic Horseshoe Crab

The Atlantic Horseshoe Crab. Limulus polyphemus. , Welcome to Slaughter Beach Horseshoe Crab Sanctuary , In April of 2004, the Town of Slaughter Beach and its residents voted to declare our town a Horseshoe Crab Sanctuary and to ban harvesting of horseshoe crabs from our beaches., We did this because residents became concerned about the dwindling numbers of horseshoe crabs during spawning season. Knowing that Slaughter Beach is prime spawning ground for this species, we wanted to reduce the pressure on the horseshoe crab population caused by harvesting and human development, and ensure that future generations continue to enjoy the yearly spectacle of their spawning., On June 12, 2004, the Town Council took the Sanctuary one step farther by approving Town Resolution Number 35: Adopting the Atlantic Horse Crab as the official symbol of the Town of Slaughter Beach., You can help… , Just flip em! , As you walk along our beaches, you may see horseshoe crabs along the shoreline, especially during their spawning season in May and June. They look a bit scary, but they do not sting or bite and cannot hurt you., Often, the surf has flipped them upside down and they become stranded and are unable to turn themselves over. When you see a stranded horseshoe, just flip 'em! Don't turn them by their tails; these are very delicate and you can hurt them. Just turn them gently from the side of their shell., How old are they? , Horseshoe crabs are an ancient species. Their closest ancestor is probably the trilobite, a creature that existed almost 500 million years ago! The horseshoe crab as we know it has inhabited our oceans for 450 million years. The species predates birds and dinosaurs., Horseshoe Crabs and Delaware Bay , There are only species of horseshoe crabs worldwide. The Atlantic horseshoe crab (Limulus polyphemus) is the most numerous and accounts for the largest percentage of the worldwide population. Limulus polyphemus can be found along the eastern coast of North and Central America, but the epicenter of spawning and population occurs in the Delaware Bay. The miles of sandy, wave protected beaches in the Bay offer optimal conditions for spawning and the tidal flats provide ideal habitat for juvenile crab growth and development., The importance of the horseshoe crab , Food for Shorebirds , Each spring, as many as a million migratory shorebirds converge on the Delaware Bay to feed and rebuild energy reserves prior to completing their northward migration. At least 11 species use horseshoe crab eggs as their primary food supply during their 2 to 3 week stopover. The birds dine mainly on eggs brought to the surface by wave action , eggs which would otherwise dry up and never develop. So while the eggs are essential to the birds, their consumption has limited effect on the horseshoe crab population., Protecting Human Drug Supplies , The horseshoe crab's copper-based blood contains a clotting factor that detects gram-negative, disease-causing bacteria. It's so effective that the biomedical product derived from it, called LAL, is used for screening all injectable medicines and devices implanted in the human body, to ensure they are free of bacterial contamination., Life Cycle of the Horseshoe Crab , Spawning Season , Each May and June, adult horseshoe crabs return from deeper waters to spawn, seeking beaches in bays and coves that are protected from surf. Peak spawning occurs on evening high tides during new and full moons., During spawning, the horseshoe crabs form clusters along the edge of the water, with as many as 12 "satellite" males grouped around one female. Females burrow into the sand and lay masses of green eggs, which are then fertilized by the males around her., Each female will return to the beach on successive tides, laying as many as 4-7 egg clusters with each tide. Each cluster, which incubates 5-8 inches below the surface, contains about 4,000 eggs. A female typically slays about 25 egg clusters each year., All the horseshoe crabs seen during spawning are fully adult. Sexual maturity occurs about halfway through their twenty-year lifespan. This late-age of sexual maturity means that anything that affects their population during spawning can have a potentially huge effect on their population for years to come., Hatching Out , Under optimal conditions, fertilized eggs "hatch out" in about 14 days. Juvenile crabs generally spend their first and second summer on the intertidal flats , feeding before daytime low tide and burrowing in the sand for the rest of the day., Growing Up , In order to grow larger, the horseshoe crab must molt and shed its shell. By the end of its first year, it will have molted several times, but will still be small , about 1/2" wide. By age 3 or 4, it will molt only once a year, sometime during July and August. These "molts" can often be found along bay beaches., Moving Deeper , As the horseshoe crab ages, it moves to deeper waters where it can find a larger food supply. These pre-adults continue to molt once a year until they reach sexual maturity. Once fully adult, they begin their annual spring migration to the spawning beaches to renew their species.