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In early May, Delaware Bay will play host to the largest swarm of horseshoe crabs on earth. Every spring for millennia these ancient crustaceans have assembled here to breed and lay their eggs, and cater to millions of migrating birds that use these eggs to fuel their continued northward migrations. But the number of crabby visitors has shrunk, due to overharvesting by humans. Hurricanes and rising sea levels haven't helped either, creating trimmer beachs that make it difficult for the crabs to breed and bury their eggs in the sand. 

This year, thanks to the work of more than 100 local volunteers and staff from several conservation organizations, the crabs will be able to lay their eggs behind a protective, man-made oyster reef. Stretching 300 feet across South Reed’s Beach in Cape May, New Jersey, the reef forms anchors for growing oysters and buffers waves to create gentler tidal zones where the crabs can breed. Channels in between the sections allow the spiny creatures to reach the beach.

“Everyone here is earning sweat equity in the well-being of the bay,” said Shane Godshall, a habitat restoration coordinator for the Littoral Society, as he led a charge of reef makers on a gusty day in April. “Lots of volunteers may not see the bigger picture of their efforts today, but they’re getting the opportunity to engage and become stewards of the environment.”

There are few bird habitats on the East Coast that are in greater need of stewardship than Delaware Bay. Once up to 12 million crabs congregated on its beaches, but after years of overharvesting, their numbers have diminished as much as 80 percent, members of New Jersey’s Conserve Wildlife Foundation say.  Following suit, shorebirds that depend on the crabs like the Red Knot, Sanderling, and Ruddy Turnstone since the ’80s. When Hurricane Sandy of the horseshoe crab habitat here in late 2012, local conservationists had to act quickly to prevent massive die-offs. The bay is a critical stopover point in the Atlantic Flyway, one of North America’s biggest geographic avenues for migrating birds.

Luckily, passion for conservation runs deep in Cape May County, and conservationists like David Wheeler were able to call on residents to point out damaged areas so they could clear away debris and put down new sand on the beaches.

“Without local expertise our projects would be much less successful,” says Wheeler, who is executive director of New Jersey CWF. “A lot of the [economic] focus in New Jersey goes elsewhere, but locals here take pride in the ecological importance of the region.”

After being hit hard by Sandy, communities around the Delaware Bay region still show signs of the hurricane’s impact. Many residents have left the coast, and area businesses and industries—aquaculture especially—are struggling to come back. Unemployment in Cape May County is currently at 17.9 percent, which is more than three times the national average. But after two years of successful restoration work, plans to restore both the bay and the local economy are starting to align.

“We’re trying to recast conservation as a community interest,” says Larry Niles, the wildlife biologist credited as the brains behind South Reed’s oyster reef. Working alongside the CWF, Littoral Society, and U.S. Fish and Wildlife Service, he hopes to galvanize more of the community to protect the bay by dredging silt from commercial waterways to build new beaches and preserving existing beaches as a first line of defense for the coast. One major perk is the “good-paying jobs” that restoration work would bring, Niles says. In like fashion, this year’s oyster reef was built using recycled conch shells bought from local fishermen, and the beach it now protects was recently restored using sand purchased from local sand companies.

By keeping the money for his programs in the neighborhood, Niles aims to support businesses with direct stakes in the well-being of the bay, and ultimately stave off the industrial pressures that have intensified species declines in the area.

“The fate of horseshoe crabs is now influenced primarily by industrial-scale exploitation,” he says, referring to the harvesting of horseshoe crab blood for pharmaceutical testing and the use of crabs as fishing bait. New Jersey passed a moratorium on harvesting crabs for bait in 2008, but Niles says that other states along the East Coast haven’t followed suit. “People looking to make money off natural resources can do so with little to no regard for the environment’s well-being.” 

In addition to local businesses, Niles says he hopes more birders can get organized in time to defend Delaware Bay. Tourism dollars, generated by birdwatching, could provide a huge lift to the region. The bay provides a direct window into the well-being of several iconic species, including the Rufa Red Knot, which in December of last year was listed on the Endangered Species List as threatened. The species has been hit on multiple fronts: the decline in horseshoe crabs, environmental damage along the coast, predators in the Arctic, and climate change. Every spring 70 percent to 80 percent of the population stops to refuel in the bay during one of the longest bird migrations in the world—9,300 miles from Tierra del Fuego, Chile, to the Arctic.

“Thanks to geolocation and tracking, we know that these birds are making six-day nonstop flights from southern South America to Delaware Bay,” says Niles, who has been studying the species for more than 30 years. “When they arrive they are at far below fat-free weights, in a completely depleted condition, and are totally dependent on horseshoe crab eggs.”

The Red Knots arrive shortly after the crabs in early May. And so, the architects of the South Reed's oyster reef were racing against more than just the incoming tide. The procession of volunteers lasted for several hours as they pulled waders on over their jeans and marched into the surf. In each hand they hoisted a black mesh bag filled with cured conch shells—the organic building blocks for the reef. More than 60,000 shells went into the surf that day, stacked in four-sided pyramids with three bags at the base of each wall.

“The stacking and shape of the shells helps the reef remain sturdy against the tide,” said Niles as he inspected a section of the finished reef. Kneeling in the surf, he pushed a spike into the sand at the corner of each pile and tightened the ropes that crisscrossed over the top. Sturdiness was key, but the reef’s real test would come when the crabs and birds arrived. Niles and his colleagues will return then to tag individuals and gather data that will measure the true impact of manmade reefs on shorebird populations. 

As afternoon moved into evening, the tide came in, and the workday came to a close. Looking back into the surf, one could see the waves breaking on the ramparts of shells. In their wake, the water was much calmer and the beach much more inviting. Now all that was missing was a few million crab eggs.

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The horseshoe crab breeding extravaganza is a sight to behold. During May and June, at either the new or full moon, these ancient creatures ride the high tide into the shallows. Using pheremones, the males and females link up and head to the beach, where the females dig their nests and drop in their eggs, which then get fertilized by the males. Get a glimpse of the spectacle in this video by Mike Fernandez.

Correction: The article previously stated that horseshoe crab numbers at Delaware Bay have dwindled to 200,000. That figure is largely unknown and instead, has been replaced by a percentage. Also, it was the U.S. Fish and Wildlife Service that participated in the reef-building event, not the New Jersey Fish and Wildlife Service.