Tracking the Wild Horseshoe Crabs of New York

By August 23rd, 2011 at 4:37 pm | Comment

Spawning horseshoe crabs (photo courtesy of US Fish and Wildlife Service)

Spawning horseshoe crabs (photo courtesy of US Fish and Wildlife Service)

On June 1, 2011 at 11:51 PM, a group of people assembled on the beach in Northpoint, New York. There was no moon shining that night, not even a sliver. The people carried flashlights or wore headlamps. They held clipboards and paper.

Their mission: to report where horseshoe crabs were spotted along the beach.

This was just one of several places along New York’s shoreline where people collect data about horseshoe crabs. Volunteers also amassed on dark beaches in Stony Brook, Staten Island, Brooklyn and Westhampton. In all, volunteers monitored the comings and goings of horseshoe crabs at ten New York beaches that night.

They are a part of the New York Horseshoe Crab Monitoring Network, a group of citizen scientists who are documenting where horseshoe crabs emerge from the water to lay eggs along beaches in New York State.  On specific dates through the spring and early summer, participants collect data about the number of horseshoe crabs and identify their size and sex. They attach tags to the horseshoe crabs bulky exoskeleton and look for tags from prior years.

While horseshoe crabs spend most of their lives in the ocean, they come to sandy beaches to spawn around the time of new and full moons in the spring and early summer, favoring areas with calm water. Male horseshoe crabs patrol the shallow water in attempts to intercept females who are headed to the beach carrying several thousand eggs under their armor-like shells. A male horseshoe crab latches onto the back (the pointy end) of a larger female and fertilize the eggs as she plows through the shallow water towards the beach. When a number of males intercept the same female, as happens commonly, volunteers with the monitoring network encounter a pile of horseshoe crabs on the beach. Volunteer have to momentarily interrupt the goings on to get an accurate count of the animals, picking up the ones on top to count the ones below. Once the eggs are fertilized, females bury them in the sand at the high tide line.

The number of quiet beaches where horseshoe crabs are able to spawn has been limited by coastal development.  Has this affected the number of horseshoe crabs that show up to spawn? Has it affected the number that roam the sea? That’s what the New York Horseshoe Crab Monitoring Network and several other long-term studies hope to discover.

The New York State Department of Environmental Conservation is interested in the data collected by these projects. Hopefully it will help the state make decisions about the best ways to conserve and manage ecosystems. Horseshoe crabs play an important role in ecosystems. While female horseshoe crabs lay a tremendous numbers of eggs each year – about 80,000 – only a few of these grow into adults. Most involuntarily become food for other animals. Shorebirds eat the eggs as well as the larvae that hatch from the eggs. Eggs that wash from the beach out to sea become food for fish and other marine life too.

The New York Horseshoe Crab Monitoring Network is run by the Cornell University Cooperative Extension and the New York State Department of Environmental Conservation.

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This post was originally published on Citizen Science Buzz, a blog on TalkingScience that highlights science projects that are helping us better understand our planet and the Universe.

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