TED HARVEY CONSERVATION AREA, Del. — The arthropod orgy was well underway when Breanne Preisen trudged over the low dune onto the narrow beach, where tens of thousands of horseshoe crabs were getting down to the age-old business of reproduction.
“There’s a female,” Preisen said, pointing at one of the peculiar sea-things crawling along an undeveloped stretch of the Delaware Bay shoreline. “She has a male attached to her.”
Every year in late spring, horseshoe crabs come ashore on the Delaware Bay Beaches to spawn. At the same time, migratory birds flying to the arctic make a pitstop in Delaware to fuel up on the horseshore crab’s eggs. This delicate balance is vital to local ecology, and is watched over by citizen scientists at the St. Jones Reserve.
Preisen inspected the cluster of horseshoe crabs more closely, then corrected herself: “Two males!” She smiled.
“It’s basically a mad dash to see who can get their boys to her girls first. That’s why they always come, just to mate. That’s it. I think it’s pretty cool.”
In one of nature’s longest-running — and oddest-looking — spring flings, spawning horseshoe crabs have been coming ashore here every May and June since prehistoric times. The shoreline is the breeding epicenter of a keystone species that’s being monitored closely by environmentalists and scientists after suffering a sharp population decline.
The ancient reproductive ritual is a surreal spectacle, with the bay’s beaches becoming crowded at high tide with harmless creatures that look like flattened Army helmets on top of hairy red spider legs. The long, bayonet-like spikes on the backs of their shells only add to the otherworldly allure of the living fossils, which leave millions of fertilized eggs in the Delaware sand each year.
Of course, there’s more than mere voyeuristic value to the Limulus polyphemus species: Horseshoe crabs and their eggs are food staples for endangered sea turtles as well as migrating shorebirds, and their unique blue blood contains an agent used to test drugs and prosthetic devices for infectious bacteria and to diagnose spinal meningitis.
“Fascinating animals,” said Preisen, 33, who grew up on these beaches and has long been enthralled by the invertebrates, which have been around for hundreds of millions of years. “I love coming out to see them.”
One recent night, Preisen and a group of volunteers stormed the beach at Ted Harvey, not far from the southeastern edge of Dover Air Force Base. Their mission: take a sample count of the horseshoe crabs that were mating just before the rise of the full moon, as the spawning cycle heats up.
When the tide reached its high point — just around 8 — the citizen scientists began heading south, split into two groups.
Eric Sawicki, a seventh-grader from nearby Magnolia, dropped a one-by-one-meter square made of PVC pipe at the waterline, crouched down, touched each of the crabs, then called out a set of numbers: “17 and 3” — 17 males, three females, which are significantly larger than the males.
Sawicki’s mother, Teresah, scribbled the figures on a census form. “That’s a pretty good count,” she said of the numbers, which would eventually be entered into a computer model to help with a broader population estimate.
Eric moved 20 meters down the beach and explained why he was out counting crabs for the third consecutive year: “I love doing anything outdoors,” he shrugged. Horseshoe crabs, he said, are bizarre but amazing.
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