Posts tagged ‘Field Notes’

Field Notes: Horseshoe Crab Monitoring at Plumb Beach

Summer intern Debra Kriensky reports on a recent field expedition

 

Molted shells from young horseshoe crabs (approximately two-to-three years old). Photo © Susan Elbin

Molted shells from young horseshoe crabs (approximately two-to-three years old). Photo © Susan Elbin

On July 23, NYC Audubon staff and interns went out to Plumb Beach in Brooklyn to help horseshoe crab researcher Mark Botton search for baby crabs. Though we couldn’t help but stop to look at the birds—we saw several oystercatchers, plenty of gulls and terns, and a flock of juvenile barn swallows—the tiny, newly hatched horseshoe crabs stole the show.

 

Though the horseshoe crab hatchlings we were looking for were in the same shape as the adult crabs we count and tag during the spawning season, they were considerably more difficult to find. Smaller than a ladybug and the same color as the sand, the crab larvae were practically invisible in the shallow waters of the low tide. Fortunately, we were able to find a few of the baby crabs, which were promptly measured and released. During our search, we also stumbled upon the molted shells of several older horseshoe crabs that likely hatched two or three years ago.

 

In addition to searching for hatchlings, Botton’s team was also there to measure

A newly hatched horseshoe crab © Debra Kriensky

A newly hatched horseshoe crab found in the shallows being held in a shell until it could be measured. Photo © Debra Kriensky

the density of eggs at different depths of sand at several points along the shoreline. Using five-cm and 20-cm cores, the group collected a total of 120 samples of sand to analyze back at the lab. This data can be used to determine where crabs are laying their eggs on the beach, among other things. For example, since birds can only reach eggs close to the surface of the sand, looking at the egg densities in the five-cm core sample can help clarify just how much of this important food resource is available for shorebirds on Plumb Beach.

 

-Debra Kriensky