Project Limulus Bringing Insights to Horseshoe Crab Conservation and Sustainable Harvest

A research effort called Project Limulus is helping to create a knowledge base about a valuable resource, horseshoe crabs. Drs. Jennifer Mattei and Mark Beekey, researchers at Sacred Heart University in Fairfield, Connecticut, organize and train a multitude of volunteers to find Limulus polyphemus along the Connecticut and Long Island shorelines, and to record information such as size, sex, mating habits and location. The animals exist on the Atlantic and Central American shores.

The ultimate goal of the project is to answer the question: Can we continue to both harvest and conserve these unique creatures?

Project Limulus volunteers, along with the researchers, attach National Fish and Wildlife Service button tags to the side of these helmet-shaped creatures to monitor the movements of the animals after they are released. The tags send a pattern of “pings” back to the researchers who can then identify the movements of individual animals. The initial tagging takes place in mid-May through June, just before and during the peak mating season. More than 20,000 animals have been tagged so far. Later, volunteers and the beachgoing public are asked to report any tagged animals found, including tag number, location and whether alive or dead. The ultimate goal of the project is to answer the question: Can we continue to both harvest and conserve these unique creatures?

a researcher places a sonar tag on a horseshoe crab

(Left) Sonar tags allow researchers to follow horseshoe crabs around Long Island Sound, each tag produces a unique pattern of pings that allow us to identify individual animals (Photo by R. Howard)

(Right) Horseshoe crabs with sonar tags awaiting release from Calf Pasture Beach, Norwalk Harbor. These particular individuals left Norwalk Harbor in August 2007. Two were heard on submersible ultrasonic receivers leaving the harbor within two weeks of release. One was heading northeast, the other southeast toward NY (Photo by M. Cunningham).

Horseshoe crabs, which are related to spiders and trilobites rather than true crabs, have existed for 400 million years, and are considered an ecological keystone species. Their eggs are a diet staple for many shorebirds, fish and invertebrates. Their numbers have greatly declined in some areas, but Connecticut had no good baseline information on their numbers, movements, and habits until Project Limulus began. Multiple partners have supported the effort, with Connecticut Sea Grant funding this summer’s work.

Students tag a horseshoe crab and later release it from the beach.

Jennifer Mattei (far right) helping students from St. Francis Elementary School and the Sound School in New Haven, Connecticut to tag a horseshoe crab. Students from both schools released the horseshoe crabs later that day from the beaches surrounding the Sound School. (Photo by L. Mattei)

This bottle contains the gel used in medical tests for bacteria. Next to the bottle is a juvenile horseshoe crab shell.

This bottle contains Limulus Amoebocyte Lysate, the gel obtained from horseshoe crab blood for use in medical tests for bacteria. Next to it is a juvenile horseshoe crab shell.

Millions of horseshoe crabs have been harvested for two purposes: bait and medical use. They are particularly effective as bait in the eel and conch fisheries along the Atlantic Coast. In Connecticut, fishermen are legally allowed to hand-harvest horseshoe crabs during a limited time of the year.

Earlier research done at Woods Hole and elsewhere on horseshoe crabs’ eyes and vision has been important in the manufacture of surgical sutures and development of dressings for burn patients. The most important medical use, however, involves harvesting their blood. Ameobocyte cells in Limulus blood are able to attach to bacteria, forming a viscous gel that prevents the bacteria from invading the horseshoe crab body. The gel is now used as a fast, efficient way to test pharmaceutical drugs for the presence of bacteria. Biomedical companies harvest blood from horseshoe crabs to produce the gel, Limulus Amebocyte Lysate (LAL). NASA is now testing the use of LAL in space to assist in the diagnosis of bacterial infections in astronauts.

Because the Project Limulus monitoring effort is community-based, it provides opportunities for people to contribute to ongoing scientific research. It also serves as an educational tool to increase awareness of horseshoe crabs and their connection to the Long Island Sound ecosystem as well as their value to human health. Many schools and educational organizations are tied into the effort.

Results so far show that male horseshoe crabs, when they emerge to mate, prefer to stay on one beach, while the females move from beach to beach. Long Island Sound animals tend to stay within the Sound region rather than migrating to the ocean, with some notable exceptions. Since a minority of males and females return to the same beach to spawn in subsequent seasons, the results suggest that creating multiple no-harvest zones in key spawning locations for conservation purposes would be a good idea.

Jennifer Mattei, Ph.D.
Chair & Associate Professor
Department of Biology
Email: matteij@sacredheart.edu
Phone: 203-365-7577

Mark Beekey, Ph.D.
Assistant Professor
Department of Biology
Email: beekeym@sacredheart.edu
Phone: 203-371-7783