Horseshoe crabs have been around for more than 200 million years -- they predate flying insects, dinosaurs and humans -- but scientists know little about them. That is changing, now that the species is playing critical roles in assuring biomedical safety and in a major environmental dispute.

In fact, there is now a Horseshoe Crab Research Center, at Virginia Polytechnic Institute in Blacksburg. The director of the five-year-old center, Jim Berkson, said the horseshoe crab historically was seen as unworthy of study because it had no culinary market, and for many years there was no obvious sign that the species was suffering a major population decline.

Two things changed. In the 1970s, a chemical in horseshoe crab blood, Limulus amebocyte lysate (LAL), was found to be useful in testing whether vaccines, intravenous tubes and implantable devices are safe for human use. A handful of biomedical companies began capturing horseshoe crabs, taking some of their blood and returning them, live, to the sea.

Then, horseshoe crabs proved useful as bait for eel and conch, two species for which there are lucrative culinary markets. Beginning in the mid-'90s, fishermen caught 2 million to 3 million horseshoe crabs for bait -- far more than just a few years earlier. An additional 200,000 were caught, bled and returned alive to the sea by the biomedical industry.

This rising catch has alarmed environmentalists, who contend that a decline in the horseshoe crab population could lead to the extinction of certain shorebirds, such as the red knot, that migrate from South America to the Arctic and time their arrivals to mid-Atlantic beaches precisely, in order to feast on horseshoe crab eggs. A fight between shorebird advocates and horseshoe crab harvesters has raged for several years.

In 2000, the Atlantic States Marine Fisheries Commission, a federally chartered regulatory body made up of the Atlantic coast states, approved a 25 percent reduction in the horseshoe crab harvest. But most participants agreed that this reduction was a guess -- a rough compromise between environmentalists, who had sought a 50 percent cut, and harvesters, who argued for no cut.

At an ASMFC meeting last month, New Jersey and Delaware jointly proposed measures that would significantly reduce the horseshoe crab take within their borders and asked other coastal states to follow suit. But many states have debated the proper course of action, often citing the lack of hard statistics for their disagreements.

"Once the resource was in crisis, the stakeholders were yelling on all sides, and the managers had to decide what to do," Berkson said. "They asked scientists, 'What do we know?' But the scientists had to shrug their shoulders, because they had no information."

What scientists do know is that horseshoe crabs are neither horseshoes nor crabs: They're considered closer to scorpions and spiders, though their closest relative may actually be the trilobite, the celebrated fossil species that flourished more than 500 million years ago.

Four species of horseshoe crab survive today, largely unchanged for 200 million years; three species live on the Pacific Rim, and one on the Atlantic seaboard. The Atlantic variety, known as Limulus polyphemus, ranges from Maine to the Yucatan Peninsula, with the greatest concentrations running from around Cape May, N.J., to Ocean City, Md.

Individual horseshoe crabs are believed to live for about 20 years. They reproduce by coming ashore several times during May and June and leaving behind perhaps tens of thousands of caviar-like eggs on intertidal beaches. Young horseshoe crabs grow in the sand for a few years before venturing progressively further into estuaries and the ocean.

However, horseshoe crabs begin to spawn only at about age 10, after traveling long distances. Some specialists fear that this complicated life cycle and migration pattern -- which served the species so well for millions of years -- might now be in danger. "If we stop harvesting today, we might not see the adult population decrease for another 10 years, and that would make it more difficult to recover," Berkson said.

In the past four years, Berkson and his colleagues have received $1 million in grants -- from five Atlantic coast states, ASMFC, the U.S. Fish and Wildlife Service, the National Marine Fisheries Service and BioWhitaker, a biomedical company. And while they are still years away from announcing definitive results, they have begun to fill the void in small ways.

So far, they have undertaken three years of horseshoe crab spawning surveys, two years of trawling counts, and a battery of tests to gauge how well the horseshoe crab can survive repeated bleedings.

The bleeding tests, done on captive specimens at Virginia Tech, have shown that taking one-quarter to one-third of a crab's blood -- volumes typical of current biomedical industry practice -- leads to mortality rates of 7.5 percent. Berkson considers that rate remarkably low. "When you think about what a human would go through if they lost that much blood, those kind of survival rates are really fascinating," he said.

Preliminary results from beach spawning surveys conducted by the U.S. Geological Survey, as well as trawling surveys by Virginia Tech, show population numbers that Berkson considers healthy -- at least for now.

ASMFC executive director Vince O'Shea frames the harvesting question as whether humans can "live off interest rather than drawing down the principal. What's exciting about Jim's work is that he's dedicated to telling us what the principal is."

In the contentious world of horseshoe-crab policymaking, most players appear to trust Berkson and his methods. "The big question is: 'How much fishery pressure can we put on the stock without damaging it?' " said Michael Millard, director of the U.S. Fish and Wildlife Service's Northeast Fishery Center in Lamar, Pa. "On that question, I would agree that Jim is an honest broker."

Berkson has not yet received funding from environmental groups, but Perry Plumart, director of government relations for the National Audubon Society, said Berkson "has tried pretty hard to come at this as a scientist. We welcome the science."

With a $650,000 federal grant approved last month, Berkson is trying to figure out how to do his population counts with aerial videography and light-sensing night scopes, and how to use radio beacons to track crab migrations.

The horseshoe crab, he said, is "an essential species for protecting our health, preserving the ecology of the Atlantic coast and keeping the coastal economy strong."