Horseshoe crabs are landing – the spawn is on

The ancient arachnid is on the rebound – so why isn’t the bird that depends upon it?

Andy Nelson – Staff
One limulus made it to shore in mid-May to spawn. The females lay thousands of eggs and males follow behind to fertilize them.

There are the Limulus polyphemus and the people who love them, this for reasons hardly obvious, for they are an ugly lot. Only their name is beautiful.

But love is blind and the horseshoe crab, the common name for the limulus, is not: it has 10 eyes, the better to see down in the deep murk of the Delaware Bay, and to poke above the surface when the tide is high, the moon full, and the beach bright with its light.

At such incandescent moments during the year, but especially in the late spring, they advance upon the bay’s many beaches like an invading army, bobbing landward under their green, helmetlike shells. It’s spawning time and before it is all over each female crab, up to 250,000 on a peak night, will have deposited as many as 20,000 eggs in the sand, with the males following behind, fertilizing them.

It is a tender mating ceremony on a beach, which coincidentally has something of a reputation as a lovers’ lane or “party beach” for young people in these rural parts. For the horseshoe, which is not actually a crab, rather a member of the arachnid clan that includes spiders and scorpions, this is a gambit to assure the perpetuation of a creature that has crawled up through the depths of Earth’s narrative. Its ancestors were here before there were dinosaurs, flying insects, flowers, and, of course, humans.

The limulus is found in Maine, Mexico’s Yucatan Peninsula, Japan, and the Delaware Bay, which supports the world’s largest population.

The specimens awaited the night of May 17 have been around only 35 million to 40 million years, newcomers. They arrived on schedule, but far fewer than expected by the man who counts them.

Bill Hall, a professor at the College of Marine Studies, University of Delaware, was disappointed. Instead of a great rush to the shore, he counted only 50 males and four females.

“I guess the ladies didn’t show up tonight,” he said, oddly apologetic to the volunteers who came to help in the count, maybe expecting a massive invasion. These were early samples of the population that reveals itself on beaches on the Delaware and New Jersey sides of the bay. The counts go on for 12 nights, timed to coincide with the phases of the new and full moons.


Dr. Hall, in khaki waders and head lamp, dropped a meter square made of PVC pipe onto the water’s edge, then counted the crabs within it. He moved 10 meters down the beach, did it again and again, up to 100 times. The same procedure was unfolding on 25 beaches of the bay. The numbers collected will be tabulated by New Jersey’s fish and wildlife service, then sent to state and federal agencies to set fishing quotas for 2009.

The crabs are sought by commercial fishermen for bait to fish for eel and conch, and by pharmaceutical companies for their blue blood, used to test intravenous drugs for bacteria. The animal can be drained of a third of its blood without harm; those who take it are obliged to return the crab to the waters it was taken from.

In the early 20th century, 4 million crabs were taken annually to grind up as fertilizer, said Hall. And in 1998 alone, 2.7 million crabs were harvested. By the mid-1990s the overall population had “crashed to about half a million,” he said, and the animal seemed headed for extinction, certain to drag other species along with it, especially the birds that live around and visit the Delaware Bay. Eventually maritime authorities responded. A crab sanctuary was established off the Delaware Bay, extending 30 miles out to sea, and running south from Atlantic City, N.J., to Ocean City, Md. Coastal states imposed sharp cutbacks in crab harvests.

Around this time the ugly crab, like the Ugly Duckling, oddly became lovely, at least to those with conservationist inclinations, or people attracted by the romance of truly ancient things.

Faith Zerbe, monitoring director of the conservation nonprofit Delaware River Keeper Network, has called it a "magical experience to stand in the dark and watch these creatures from 400 million years ago stream up out of the water.”

Hall began his annual census in 1991. Volunteers arrived in the hundreds to save the crab – people like Glenn Gauvry, a conservationist with an affection for the limulus who organized a group to defend it and rallied people to the beaches with the slogan, “Just flip ’em” (if you see a crab helpless on its back, flip it over).

Now New Jersey totally prohibits fishing the limulus. Delaware’s limit is 100,000, males only. Maryland’s quota is 170,653, Virginia’s 152,495. This year, Ms. Zerbe happily announced “a major shift” – a horseshoe crab population increase due to the fishing moratoriums.
Indeed, the census counted almost 2 million.

Many people concerned with such things are satisfied with the management of the crab. Others argue that continuing to take half a million of them from the region’s waters every year is hardly good for the species, and for the animals that depend upon them. “The crab,” said Hall, “is a keystone species. Everything from minnows to sharks feed on its eggs; rockfish, flounder, turtles.”

But mostly birds do, tens of thousands of them, migratory species that visit this time of the year and those that live here permanently. There have been significant falloffs in recent years among species, like the ruddy turnstone, sanderling, and golden plover. Most dramatic is the population drop of the red knot, a small, red-breasted bird that winters in Tierra del Fuego and breeds in the Canadian Arctic. Between 1982 and 2006, its numbers fell from 140,000 to 40,000.

The bird strives to arrive in the Delaware Bay when the horseshoe crabs are planting their eggs on the beaches. It is a vital rendezvous. Without sufficient crab eggs to regain weight lost during its flight out of the south, the red knot can’t reach its breeding grounds in the far north.

Those opposed to the current policy believe a total prohibition against fishing the crab would slow these falloffs.

Larry Niles, of the Conserve Wildlife Foundation of New Jersey, wants a total moratorium because, he said, “Maryland and Virginia are taking crabs from the Delaware Bay by catching them before they migrate here to spawn.”

Whether an additional half million crabs in the sea would help the birds isn’t certain because, as Hall said, “Nobody really knows what’s causing this bird loss. It could be pollution, or something going wrong outside the area.”

Frank Eicherly, a former commercial bait fisherman who said he was squeezed out of business by current moratoriums, also thinks something else is killing the birds. He noted that over his long years as a waterman the birds sometimes failed to arrive when the crabs were spawning. If the limulus is late and fails to seed the sand with its eggs while the birds are there, the birds, though underweight, will depart northward, obedient to the imperative of their instincts.

That is what is happening this year. “So far the crab counts have been really low,” Hall reported last week, noting that storms in early May could have kept them from coming ashore. Meanwhile, most of the migratory birds have left. “I suspect this is going to be a bad year for the birds.” The limulus protects itself before all others. It knows the danger of landing in a rough sea. It has weathered all threats and defeated all obstacles through countless millennia.


To Stewart Michels, a biologist at Delaware’s Department of Natural Resources, the current situation offers a lesson in the evolutionary process: “The bird is specialized and perfectly adapted to things as they are. The crab is much more adjustable, a master of survival.”

The lesson: The perfectly adapted creature is the first to die when the situation changes.

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