July 16, 2023 — The horseshoe crab starts its extraordinary annual migration to the East End not in Manhattan but on the continental shelf, in the dark, under hundreds of feet of water. Some ancient instinct, strengthened over nearly 500 million years of life on earth, tells it to begin, and over the course of months it edges closer to our shoreline, until the waters become shallow and the crab’s days slowly brighten.
On a full moon tide in May, its journey is complete, and along the bottom of our bays, hundreds pair off. The smaller male attaches to the larger female, who finds a suitable beach to lay her eggs. She buries herself five to 10 centimeters into the sand and deposits upward of 10,000 eggs before the male fertilizes them.
“She drags him around. He’s sort of along for the ride,” said Matt Sclafani, who works for the Cornell Cooperative Extension, and runs the horseshoe crab monitoring network in New York on behalf of the New York State Department of Environmental Conservation. “The female pumps the water with her gills to help increase the fertilization success.” Satellite males, unattached to the female, also can externally fertilize some of the eggs.