The eager team of taggers arrived at the Town Beach last Friday ready for a cold, windy evening of work wading in the cold, shallow water-and looking for horseshoe crabs. The taggers were equipped with the tools of the task: sweatshirts, shorts, numbered metal tags, a tagging tool, and flashlights. Their goal? To find and place unique tags in the shells of the Limulus polyphemus (horseshoe crab) specimens they could find. Once tagged, the horseshoe crabs would be released to fulfill their mission: to lay many millions of eggs on the beaches of Old Saybrook.

"The crabs are cued [to lay their eggs] by the lunar cycle-new moons and full moons-and when the temperature of the water in Long Island Sound rises above 60 degrees," said Penny Howell, a fisheries biologist with the state Department of Environmental Protection (DEP). "The most vulnerable time for horseshoe crabs is when they come out of the water [in May and June] to spawn. Each crab will lay millions of eggs. The eggs then provide a key source of food for migratory shore birds."

But the lowly Limulus polyphemus provides more than just food for the migratory birds' journey north (a bird's weight can double from eating horseshoe crab eggs on its stopover). In the blood of the horseshoe crab is the key ingredient used in 90 percent of the toxicity testing of injectable medicines by pharmaceutical companies. An agent in the blue blood of the horseshoe crab is extremely sensitive to the presence of harmful bacteria called endotoxins that can contaminate an injectable medicine.

As Bill Hall, a marine education specialist for the University of Delaware Sea Grant College program wrote in 1999, "This animal's blood contains a unique clotting agent that the pharmaceutical industry uses to test intravenous drugs for bacteria. No IV drug reaches your hospital pharmacy without its horseshoe crab test."

This then is the imperative that drives the annual tagging and census of horseshoe crabs: the need to protect the population of horseshoe crabs to save human lives and maintain the strength of migratory shore bird populations.

"Over 10,000 horseshoe crabs have been tagged in Long Island Sound. About 12 percent of specimens found have already been tagged once," said Howell.

So far, Howell said the Sound population of horseshoe crabs appears stable overall; population levels in the eastern Sound have dropped somewhat, but have increased in the western Sound.

"Horseshoe crabs live for 20 years and are 9- to 10 years old before they mate. They're scavengers that eat clams and oysters," said Howell, who noted the species's food source can lead to conflicts with shellfish fishermen who view them as a threat to their livelihood.

But on this Memorial Day weekend in Old Saybrook, all that mattered to the volunteers was the tagging of the horseshoe crabs that came ashore for their annual ritual.

As the volunteers walked the shallow waters that Friday evening, two parents held a taut length of rope to mark the extent of each search grid along the beach, counting off starting with Grid 1 and reaching to Grid 45 at a point near Harvey's Beach. While Friday evening's team found only a few limulus specimens, a Saturday morning team of volunteers found and tagged more than 30 horseshoe crabs.

Several Girl Scouts working on their Silver Award were among the volunteers helping John Ogren of the Old Saybrook Land Trust and DEP's Penny Howell that Friday evening to attach metal tags to the horseshoe crabs' shells. The tagging program is part of Project Limulus, a program of Sacred Heart University that has collected data on the movements and population of horseshoe crabs in Long Island Sound since 2003.