Mating By Moonlight: Horseshoe Crab Counting with New York’s Citizen Scientists

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As the pinkening sun slipped behind the Manhattan skyline, a group of citizen scientists in waders paced along a scruffy rim of shoreline overlooking Jamaica Bay, attempting to tally some of the first-ever New Yorkers.

During the months of May and June, the prehistoric horseshoe crab — whose ancestors predate dinosaurs — make their annual pilgrimage to the banks of the mid-Atlantic, including coastal areas across New York City. There, they lay clutches of thousands of eggs in sandy holes before returning to the depths of the ocean.

During that time, teams of volunteers fan out across the waterfronts of Staten Island, Brooklyn, and Queens during high tide before and after the new and full moons to count crabs during their fornicatory frenzy.

On a blustery late spring evening, the coastline of the aptly-named Sunset Cove Park in Broad Channel, Queens is teeming with the ten-eyed, 12-legged creatures — which are not, despite their name, actually crabs but rather arthropods with exoskeletons that are more closely related to spiders. They bob in and out from shore along salty waves, clamoring over one another.

Teams of volunteers traced the sliver of beach, dodging hunks of pavement and debris, and ducking under the lines of fishermen waiting for bluefish to bite. After measuring their steps at appropriate intervals, they count the number of crabs in a given square meter area, jotting down the number of male and female crabs in those sections of beach.

Females are larger than the males, while males have a special set of claws that help them latch onto the female’s shell while fertilizing eggs. Young crabs, distinguished by their slicker shells, molt more than a dozen times before they begin mating at around 10 years old. Crabs can live up to 25 years, with more barnacle growth on shells often indicating an older specimen.

“I’m standing on a beach holding a prehistoric crab, when three hours ago I was sitting at a computer,” said volunteer Sabine Frid-Bernards, 35, who lives in Bedford-Stuyvesant. “Feels like a good reminder that there’s still nature in this city.”

‘Totally Harmless’ and Sometimes Super-Helpful

Though you wouldn’t know it by the squirming masses writhing along the shoreline, the American horseshoe crab is considered a vulnerable species by the International Union for Conservation of Nature.

Their eggs are an invaluable food source for migratory birds, like the red knot, which travels annually more than 9,000 miles from the furthest reaches of South America to the Arctic circle, making a last stop on the mid-Atlantic coast , before completing their journey north.

Humans rely on the horseshoe crabs, too. They’re used as bait for commercial eel and conch fisheries . And pharmaceutical companies extract their blue blood , which contains a chemical used to detect bacterial contamination in vaccines and on surgical implants like pacemakers , though harvesting the creatures for pharmaceutical purposes is strictly limited in New York State, according to the the Department of Environmental Conservation (DEC).

A synthetic alternative for their blood is already used widely in Europe, and may begin to reduce the reliance on horseshoe crab blood here. But in the meantime, authorities rely on the annual censuses to help set thresholds for how many can be harvested each year.

The data collected by NYC Audubon and NYC Parks is ultimately sent to the New York Horseshoe Monitoring Network , a collaboration of the state DEC and Cornell Cooperative Extension,  which collects counts from New York City and other locations along Long Island , and helps the state’s conservation efforts.

On June 8, the creatures’ fans will celebrate them and their conservation efforts with a special event: the Jamaica Bay Horseshoe Crab Festival . It’s free and open to the public, to coincide with their summertime mating ritual.

“Everybody who’s had a vaccine, or a pacemaker, or a needle go in their body, they’ve been tested for bacteria. And so we all kind of owe [horseshoe crabs] a thank you,” said Zach Bailey, 30, a National Parks Service ranger and volunteer coordinator for the Jamaica Bay Wildlife Center, as well as a volunteer counter himself. “They’ve been around for longer than trees.”

To him, it would be “so sad” if humans “took out this thing that survived multiple mass extinctions.”

Some of those counting are new to the crab, like Katherine Chen, a manager of Community Science & Collision Reduction at NYC Audubon, who grew up in Ohio and was helping oversee the crab census for her second consecutive season.

“I didn’t know they existed,” Chen said, adding she’d become a fast fan. “It’s really amazing to see.”

Others like Bailey, have a lifelong affinity for the creatures. So much so that he had one tattooed on his right forearm. Bailey grew up on the Jersey shore, more fertile terrain for horseshoe crabs, and adored showing them off to startled out-of-towners when they’d visit.

“Everybody’s scared of them inherently, but they’re totally harmless,” he said. “They could use a little help if you see them looking scary. That means they’re upside down and they’re out of the tide and maybe need a little assistance getting back to the water.”

Celebrate the horseshoe crab at an upcoming Jamaica Bay Horseshoe Crab Festival at Sunset Cove Park on June 8 , or take part in an upcoming counting event with NYC Audubon at Plumb Beach or in Broad Channel through June 23 or with NYC Parks in Coney Island and Staten Island through June 21.

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