The Atlantic Horseshoe Crab

The Atlantic Horseshoe Crab. Limulus polyphemus. Welcome to Broadkill Beach Horseshoe Crab Sanctuary
The beach, waters of the Delaware Bay, and the natural surroundings of Broadkill Beach have been beckoning people to enjoy its bounties since colonial times.

Our earliest recorded reference comes from the diary of Mrs. Aletta Clarke on May 24th 1790 when she wrote of a "great meeting" on the beach with cakes, raisins, meat, bread, and rum. Broadkill Beach slowly progressed from crude shacks built by fishermen for temporary shelter, to weekend cottages accessed by a foot bridge that crossed the Broadkill Sound, now called Deep Hole Creek. Over the years it grew from a weekend haven into the modern community it is today.

Nestled between the waters of the Delaware Bay and the marshes and forests of Primehook National Wildlife Refuge, it is only natural for the people of Broadkill Beach to be keenly aware of their environment and the responsibility of its stewardship. In so keeping, in partnership with the Ecological Research and Development Group, a Horseshoe Crab Sanctuary was established here at Broadkill Beach in the year 2000.

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.