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International Horseshoe Crab Day

Friends of Greenwich Point teamed up with Sarah Coccaro of the Greenwich Conservation Commission for a unique opportunity to learn more about horseshoe crabs and their benefits to our coastal ecosystem.  On the shores of the Old Greenwich Yacht Club on June 20th, residents joined Sarah to count horseshoe crabs and discover more about these fascinating living fossils in our backyard.   


FGP: What are your favorite fun facts about horseshoe crabs?

SC: These creatures are hundreds of millions years old and have evolved very little in that time. For 300 million years, they've remained essentially the same.  For this reason, they're known as living fossils. There are actually only four species of horseshoe crabs in the world. The species we find in Greenwich is the same as the one in Florida and all along the East Coast.  


FGP: What kind of studies are underway about horseshoe crabs in the Long Island Sound?

SC: For over 20 years, Project Limulus has been led by Dr. Jennifer Mattei at Sacred Heart University. One feature of Project Limulus is a citizen science population study. During the new and full moons in May and June around high tide, residents are encouraged to count the horseshoe crabs in their communities and report their findings. Another part of the project is horseshoe crab tagging, which the Conservation Commission has long participated in along with other local organizations. Females are tagged more often because they have a slightly bigger body and live longer, so there's a better chance they'll be found again. Each tagged horseshoe crab has a specific data sheet with the tagging location and date, crab size, male or female and shell condition.  


FGP: What should residents do if they find a tagged horseshoe crab?

SC: Residents should call 1-888-LIMULUS and report the tag number, location (specific beach), date the crab was found and if the crab was alive or dead.  Live crabs should be returned to the water. You can also enter the information online at the USFWS website or email Horseshoe crabs come to shore to spawn, but then we don't generally see them again in the Sound once they leave.  Their primary mode of mobility is walking on the ocean floor, although they can launch themselves through the water for short distances using "book gills." Even with their limited mobility, they can go far distances.  I've even found one first tagged in Maryland.


FGP: Why should we care about horseshoe crabs?

SC: These creatures are very important to our ecosystem, a critical part of the food web. Migrating birds, like the red knot, depend on horseshoe crab eggs I've also seen eels feeding on them. Beyond this, the species plays a critical role for human health.  Horseshoe crab blood is used to test for contamination in everything from shots and IV drips to implanted medical devices and even vaccines for COVID-19.  Their blood will clot quickly when exposed to toxins in bacteria, making it invaluable for medical testing.  We are truly indebted to these ancient creatures.


FGP: What are their greatest threats?

SC: In Greenwich, one of the biggest problems is predators, especially raccoons. The crabs are defenseless against these animal threats. But this year we noticed a significant increase in the crab population at Greenwich Point because of the decline in raccoons due to the distemper outbreak over the winter.  In one hour, we counted over 200 horseshoe crabs!  The other threats include over harvesting and habitat loss.  But seeing residents' interest in this species and increasing understanding of their value makes me optimistic for their future.

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