June 18th 2021

Strong tides from new and full moons strand thousands of horseshoe crabs along the Delaware Bay shore in Cape May County each year. And then they mate.

The Delaware Bay is home to the largest horseshoe crab spawning location in the world, according to the U.S. Fish and Wildlife Service. Its beaches have a sand and pebble mixture perfect for incubating horseshoe crab eggs.

During spawning, a female crab will partially bury herself in the sand while she lays a cluster of about 4,000 tiny green eggs.

When the female crabs crawl ashore to lay their eggs, flocks of hungry, migrating shorebirds take notice. Red knots, ruddy turnstones and semipalmated sandpipers rely on the crab eggs for a rich food supply.

Why This Matters

Horseshoe crab blood is used to test the safety of vaccines and other drugs, according to the Ocean Conservatory. These creatures don't have white blood cells to help fight off infection, they have what's called amebocytes, which are little cells that attack pathogens.

This keeps the disease from spreading throughout the organism.

In the late 1950s, a physician at Johns Hopkins discovered that you can use the amoebocytes found in horseshoe crab blood for safety tests. Essentially, amebocytes are added to the contents of the vaccine or drug, and if they excrete their defense mechanism, it means the product isn't ready for use yet, because the specimen contains bacteria encountered by the amebocytes.

After they feed, the birds fly on to their summer breeding grounds in the Arctic Circle.

This ritual is more than 400 million years old, NJ.com reports. New Jersey closes a few beaches for the shorebirds during their peak time, typically May 8 to June 8, including Sunray Beach.