Despite its name, the horseshoe crab isn't a true crab at all. In fact, it's more closely related to the spider and the mite. 

Nor, despite its name, has the horseshoe crab been very lucky of late. When the ancient creature isn't being chopped up and used for bait to catch eels, conch and catfish, its blood is being sucked in the name of medicine.

Coastwide, horseshoe crab harvests have increased dramatically in the past decade, soaring from 1 million pounds in 1990 to 4.5 million in 1996. That has biologists worried that the stock, which is concentrated in the mid-Atlantic between Virginia and New Jersey, may be in decline - something that threatens not only the horseshoe crab, but a variety of species that depend on them.

Reacting to that concern, Maryland Gov. Parris Glendening put forth emergency regulations that would slash the state's horseshoe crab landings from a high of 2.6 million pounds in 1996 to no more than 750,000 pounds.

"Although horseshoe crabs are neither valued for their beauty, nor their delectable taste in seafood dishes, they serve an integral role in the marine ecosystem," Glendening said.

Harvests off the Maryland coast had grown rapidly, particularly as New Jersey and Delaware took actions to curb horseshoe crab harvests.

Biologists have become concerned that not only were the harvests excessive, but demand for the crabs could soon push harvest efforts into the Chesapeake and coastal bays - areas mostly untouched by harvest activities so far.

"Currently, there is not a big fishery in the Chesapeake Bay and the coastal bays, but with market demands, that could change," said Tom O'Connell, a biologist with the Maryland Department of Natural Resources.

"These regulations will help prevent that fishery from developing." Horseshoe crabs can live up to 18 years, but don't reproduce until they are 9 to 12 years old. Like other late-maturing species, that makes them subject to overharvest. It also makes efforts to rebuild the stock a long, drawn-out process that can take decades.

Although the exact status of the stock remains unclear, several surveys indicate that the abundance has dropped as harvests increased in recent years. Horseshoe crabs are primarily harvested so they can be chopped up and used for bait in the eel, conch and - to a lesser degree - the catfish fisheries.

But the species is critical for the survival of migrating shorebirds that stop on wide sandy beaches and eat crab eggs dug up by other crabs during during the intense nighttime horseshoe crab spawning activity that takes place around the time of the full moon in late spring and early summer.

Delaware Bay is not only the largest breeding area for horseshoe crabs, it is also one of the most important stopping points for migrating shorebirds - such as red knots, sandpipers, turnstones and plovers - whose arrival in mid-May and June coincides with the peak of the horseshoe crab mating period. Annual surveys in Delaware Bay have observed a drop in shorebird abundance from nearly 500,000 in 1986 to about 200,000 last year.

At least 20 species of shorebirds rely on horseshoe crab eggs to replenish their body fat during their trip to breeding grounds in Canada. A loss of horseshoe crabs, biologists say, would leave the migrating birds without the necessary food supply to complete their trip.

O'Connell said that many of the horseshoe crabs that breed on Delaware beaches are thought to spend much of their life off the Maryland coast.

In addition to shorebirds, adult horseshoe crabs also form a significant part of the diet of juvenile Atlantic loggerhead turtles, a threatened species that uses the Chesapeake Bay as a summer nursery area. A variety of other species also consume the horseshoe crab at various stages of its life.

Humans, too, depend on the horseshoe crab. Scientists have used horseshoe crabs in eye research, surgical sutures and wound dressing development.

Their blood is used to detect bacteria in drugs, a test that must be done on every manufactured drug.

Several hundred thousand horseshoe crabs are caught and bled for that purpose each year. Although this is not fatal to the animals, and they are required to be returned to the environment, studies show the bled crabs have about 10 percent greater mortality than unbled ones.

The horseshoe crab is an ancient creature that has been around almost unchanged for roughly 360 million years. Glendening said the new regulations "will ensure that this extraordinary creature, which has already survived hundreds of millions of years, will continue to fascinate and benefit future generations as an integral element of the Chesapeake Bay's ecology, and as a continuing contributor to advances in medial research."

The emergency regulations, which went into place on April 10, after approval by a legislative committee, not only caps the amount that can be landed in Maryland at 750,000 pounds - the average annual catch from from 1985 to 1996 - but also closes waters within a mile of the state's Atlantic coast to harvest from April 1 to June 30, which is a critical time to spawning.

In an effort to minimize the impact on fishermen, the state will only issue no-fee commercial permits for horseshoe crab harvests to fishermen with a prior history in the fishery. The regulations also set specific seasons, daily landing limits and area restrictions for harvesting. People harvesting horseshoe crabs for medical research will be exempt from landing limits.

A hearing is scheduled for the regulations on June 3, after which they could be modified. Changes could also be made when the Atlantic States Marine Fisheries Commission - which represents all East Coast jurisdictions - adopts a coastwide management plan for horseshoe crabs this fall.

Both New Jersey and Delaware have established restrictions aimed at reducing the horseshoe crab harvest, but neither state has set an absolute limit on the total catch.

Virginia has not had a significant fishery for horseshoe crabs in recent years, although O'Connell said there were some concerns that harvest restrictions in other states could boost fishing efforts there.

Maryland's action was immediately hailed by environmental groups. "With the migratory birds already winging their way here and the horseshoe crabs about to spawn, these regulations are in the nick of time," said John Flicker, president of the National Audubon Society.

Flicker noted that bird watching is an increasingly important economic activity, with individuals spending more than $500 million on wildlife watching activities in Maryland in 1996, according to U.S. Fish and Wildlife Service figures.

"Saving the horseshoe crab will provide economic and environmental benefits," Flicker said. "More and more people are embracing bird watching as a recreational activity. Saving the horseshoe crabs is important for Maryland's recreational economy."