Learning About Horseshoe Crabs at the LIMM

The recently held a lecture on horseshoe crabs  presented by Dr. John Tanacredi, chairman of the department of Earth and Marine Sciences at Dowling College in Oakdale. Prior to his work at Dowling in 2001, Dr. Tanacredi was a research ecologist for the National Parks Service and also an environmental analyst on Governor’s Island.

The program, entitled “Limulus in the Limelight,” helped to shed some light on the importance of the horseshoe crabs. There are four different species of horseshoe crabs, two of which are consumed in Asia. Horseshoe crabs are said to be 455 million years old, and they have survived two mass extinction events. They aren’t crabs or crustaceans, but horseshoe crabs are in their own class.

Horseshoe crabs are also extremely useful to humans. “The blood of the horseshoe crab is a true blue blood; it’s not iron-based,” Dr. Tanacredi said. “Their blood contains LAL, a bacteria collecting element.” Horseshoe crabs are additionally a food source for migratory birds.

Horseshoe crabs are also used for bait for eel and conch. They are not an endangered species, but their numbers have been on the decline. Before the 19th and 20th centuries, the harvesting of horseshoe crabs didn’t have an impact on their population. More recently, it seems to have had an effect. New York doesn’t have a moratorium on horseshoe crabs so many people are catching them here and bringing them up to Massachusetts or Maine, where they are bleeding them for LAL and selling them for bait.

You are unable to tell if a horseshoe crab is a male or female until their appendages mature at 10 years of age. Their breeding period is synchronized to the lunar cycles. June and July is the peak breeding period and a single female can lay 80,000 eggs per season. “Females release their eggs into the sediment,” Dr. Tanacredi said. “The female can penetrate the sediment and the nest can be in different layers.”

The largest population of horseshoe crabs can be found on the Delaware Bay. Interestingly, horseshoe crabs are only found on the east side of continents. They are found in India, Asia, Mexico and the East Coast of the United States.

Dowling College is planning to release 10,000 crabs per year into the Great South Bay. They are leasing space in the Boat Basin at the LIMM and are captively breeding horseshoe crabs from eggs. Dowling College has also been conducting studies of the horseshoes crabs on 65 different beaches on Long Island from the tip of Brooklyn to the tip of Montauk.

“We have been taking inventory of the horseshoe crab population,” Dr. Tanacredi said. “The trend shows they are declining over the last few years and the numbers show the population is down over the last decade.” Currently they are breeding about 400 horseshoe crabs in the hatchery.