Project Limulus (Horseshoe Crab Monitoring)

Horseshoe crabs (Limulus polyphemus), described as “living fossils,” are actually more closely related to spiders than crabs. Although they have been around since before the dinosaurs, little is known about their population dynamics and mating patterns in the Sound.

That’s changing thanks to Project Limulus, a monitoring project being conducted by Jennifer Mattei, an Associate Professor and Chair of the Biology Department at Sacred Heart University in Fairfield, Connecticut.

Her research uses “citizen scientists,” including local volunteers, elementary school teachers, and students to help tag horseshoe crabs as they appear in the spring on Connecticut beaches for spawning. Since 2000, dozens of volunteers have applied more than 10,000 tags to the shells of Limulus and reported more than 650 recaptures.
So far what Mattei’s monitoring teams have found is not good news for the horseshoe crabs. They have consistently found that only 40 percent of the spawning population is female. And of the total population, not all are mating. For example, in 2005, only 57 percent of the 2,200 horseshoe crabs tagged at Milford Point in 2005 were found as mated pairs. The monitoring reveals the potential for a declining population. It also shows that in 2005 only three pairs had one additional male as a potential mate nearby, pointing to another problem that could lead to a decline in the loss of genetic diversity. In Delaware Bay most females mate with clusters of males.

“In Delaware Bay, DNA analysis has revealed that at least three different males may fertilize the eggs in one nest so the genetic diversity of those eggs is quite high,” said Mattei. “Conservationists and ecologists know from experience in managing other economically important species that the higher the genetic diversity, the healthier the population.”

Protecting the species is important to the Sound’s ecosystem. Numerous shorebird species find sustenance by eating the horseshoe crab eggs left in shallow nests on the beach between high-and low-tide lines. In water, a horseshoe crab acts as an “environmental engineer,” using claw-like appendages to dig up nutrients in the sea floor and circulate them in the water. Because of the food supply it generates, about 20 marine animals, including flatworms, blue mussels, barnacles, and sponges live in or around its shell.

Project Limulus has received funding from the Connecticut Long Island Sound License Plate Fund, Wildlife Trust, Sacred Heart University, and LISS, through the Sound Futures Fund. Participating volunteer groups include the Sound School in New Haven, which provides high school volunteers and boat time to help Mattei track the movements of the crab underwater utilizing sonar tags and sonar monitoring equipment.