The horseshoe crab isn't really a crab at all; it's a relative of spiders that has existed virtually unchanged for more than 200 million years. The animal is used for photoreceptor research (see "Sex, Eyes, and Videotape," ScienceNOW, 17 November 1997 ), and its blood is important in testing injectable drugs for bacterial contamination.
The crabs usually live in deep water off the coast, then come to the beach to spawn in the spring. In the Delaware Bay area, so many females bury their eggs on the beach that many are accidentally dug up by crabs that arrive later. Famished birds migrating to the Arctic gorge on as many as 9000 of these eggs a day to regain their body weight. "It's a large feast table of eggs that would never have hatched," says Glenn Gauvry, director of Ecological Research & Development Group Inc., a wildlife conservation organization based in Milton, Delaware.
Gauvry's group has conducted surveys that suggest "a dramatic decline" in the number of horseshoe crabs coming ashore in recent years. Two years ago, a habitat management plan, commissioned by the Atlantic States Marine Fisheries Commission, found that the populations were at best stable and probably declining. And this year, according to Perry Plumart of the National Audubon Society, which has been lobbying states and the federal government to protect the crabs for several years, many migrating birds did not leave at their normal body weight--suggesting that fewer eggs were available.
Despite the lack of rock-solid evidence, the Department of Commerce yesterday formally proposed setting up a federal preserve off the mouth of Delaware Bay on 30 October. "We look at it as a risk-averse approach," says Paul Perra, a fisheries biologist and manager with the National Marine Fisheries Service. Conservation groups are hailing the decision. "Protecting the spawners off the Delaware Bay is very sensible," Gauvry says. "It's the heart of the population."