Ancient Undersea Creatures
The odd Boston Globe headline read, “Chaperones Needed for Horseshoe Crab Mating Season,” after Massachusetts marine officials reduced the number of crabs that anglers can use as bait for eel- and conch-catching -- launching a spawning survey so the public would weigh-in when horseshoe crabs were seen in late Spring.
Horseshoe crabs, who have evolved little in 250 to 350 million years, may be disappearing. There’s a ban on catching them for bait in New Jersey and South Carolina.
Atlantic horseshoe crabs, sometimes called living fossils, aren’t really crabs. They’re related to spiders. Four species of horseshoe crabs survive today; Atlantic horseshoe crabs are the only ones in North America. They live along the western shores of the Atlantic Ocean and in the Gulf of Mexico.
The crabs migrate to shallow coastal waters with soft sandy or muddy bottoms during the late Spring breeding season, which is when my enthusiasm for them is kicked into high gear.
Each May and early June during the high tides, three days before and after a new and
full moon, female horseshoe crabs descend on our Connecticut shoreline, coming ashore or staying in very shallow water to lay their blue-green eggs. Gathering on the shore, female crabs dig holes and deposit tens of thousands of eggs. Male crabs, two-thirds the size of females, positioned along the water’s edge as females arrive, hang on to the female’s shell with their glove-like claws as they’re pulled up the beach to the high-tide line, and fertilize eggs as they’re dragged over the nest. After the mating ritual, female crabs and attached males (sometimes more than one), leave the beach as waves wash sand over the nest.
The eggs that last beyond meals for shorebirds take about two weeks to hatch.
At least 11 migratory species of shorebirds feed on thousands of horseshoe crab eggs each day during the crabs’ stopover, and these protein-rich eggs provide the energy shorebirds need for their continuing flights to breeding grounds. The fates of shorebirds are tied to the abundance of horseshoe crabs. Biologists say red knots (migrating shorebirds who are also the targets of hunting in South America) are at risk of extinction because U.S. anglers catch horseshoe crabs for bait, and crab eggs are important food for migratory birds.
After millions of years, horseshoe crabs have survived because of their hard, curved shells, difficult for natural predators like sea turtles to overturn. Despite capture for biomedical eye research and for bait, they have also survived because they can endure a year without feeding (on worms, mollusks, crustaceans or small fish).
The federal government moved to protect these crabs, in part, by designating a 1,500-square-mile horseshoe crab preserve extending 30 nautical miles out into the Atlantic Ocean — from Peck’s Beach, New Jersey, to Ocean City, Maryland. This area is habitat to the largest horseshoe crab population on the east coast.
If you find a horseshoe crab on the beach this summer, flipped over with legs up in the air, offer this ancient mariner a hand by turning the crab over before curious children approach. You can also help these crabs and all marine animals by keeping trash out of the ocean, and picking up litter.
I hope your summer is enjoyable and includes some intriguing interludes with Nature.