The food web around the horseshoe crab—one of Earth's oldest species—is beginning to unravel, scientists say.
Certain species of migratory shorebirds depend on excess crab eggs to fuel the final leg of their spring journey to the Arctic. Researchers are concerned the birds are in jeopardy.
"Right now we're in that real dangerous period where nobody can say what's going to happen for certain," said Larry Niles, a biologist with the New Jersey Division of Fish, Game, and Wildlife in Trenton.
The birds feed on the crab eggs in the Delaware Bay, an estuary sandwiched between New Jersey and Delaware (map) that harbors the world's largest horseshoe crab population. But human harvest of horseshoe crabs has reduced the egg surplus.
In the race to keep birds—especially the red knot, which feeds exclusively on the crab eggs—from extinction, scientists and fisheries managers are considering increased protections for the crabs.
The crabs, which look like a hoof of a horse, are more closely related to extinct arthropods than to other crabs. Horseshoe crabs date back at least 360 million years and perhaps longer.
"They're quite the ancient critters, and they haven't changed for millions of years," said Michael Haramis, a wildlife biologist with the U.S. Geological Survey (USGS) in Laurel, Maryland.
Mark Botton is a biologist who studies horseshoe crabs at Fordham University in New York. "The conservation concern is not so much for the horseshoe crab itself, but rather that the population is big enough to provide lots of eggs," he said.
Collapsing Populations
In 1992 the Atlantic cod fishery collapsed. With no cod to catch, fishers started to go after conch. "And the best bait for conch was horseshoe crab," Niles, the New Jersey biologist, said.
As the conch harvest expanded, so too did the horseshoe crab harvest, he added.
By the mid-1990s the annual horseshoe crab harvest increased to 2.5 million from a few hundred thousand. The horseshoe crab population plummeted. Density dropped 90 percent, according to Niles.
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