The Horseshoe Crab Spawing Survey

Unique Characteristics of Horseshoe Crabs

Why do we study horseshoe crabs? There are many reasons. To begin with, horseshoe crabs, known to scientists as Limulus polyphemus, are one of our oldest living life forms, dating back before the time of the dinosaurs. In their larval stage, horseshoe crabs resemble trilobites, fossils which date back 500 million years. Although they are called crabs, they in fact are not true crabs but have their own genus. They have been of interest to science because they are ancient, unique and have characteristics unlike other species. Horseshoe crabs are known to have a highly complex ocular system with six pairs of eyes, or light sensors. Additionally, the blood of horseshoe crabs is of value to medical science because it contains the property LAL (Limulus Amebocyte Lysate) which is harvested by biomedical labs and used to test the sterility of surgical instruments before surgery. Within the ecosystem, horseshoe crabs play an important role as well. Migrating shore birds, in particular the endangered Red Knot, which flies from Chile to the Canadian Arctic where it breeds, depend on a stopover along the New Jersey, Delaware, Maryland coast to feed on freshly laid horseshoe crab eggs in order to complete their journey.

Why We Need a Spawning Survey?

Horseshoe crabs are also valued by fishermen who harvest spawning females to use as bait for eel and conch. In recent years, decline in the population of Red Knots has been attributed to overharvesting of the spawning horseshoe crabs, thus depriving the birds of the necessary protein to complete their journey north. This latter circumstance is what prompts the DEC to fund the Horseshoe Crab Spawning Survey in order to determine the how the horseshoe crab population is trending. Data gathered from the survey informs the DEC how best to regulate harvesting permits for fishermen. In Delaware Bay, a major stopover site for the Red Knot and other shorebirds, the situation has now been determined severe enough to ban harvesting completely. In New York State, the permitted catch has been reduced but not completely eliminated. At West Meadow Beach, however, the DEC has responded to requests by the Town of Brookhaven to forbid harvesting at that site during the spawning season. This regulation goes into effect in 2007 for the first time.

How the Survey is Managed?

The Horseshoe Crab Spawning Survey is funded by the New York State Department of Environmental Conservation and began in 2005. Kim McKown, the Director of Crustaceans for the Marine Resources Division of the DEC , together with her staff biologists, Robyn Burgess and Sandra Dumais, work with Dr. Matthew Sclafani from Cornell University Extension, who is hired by the DEC to design and conduct the study. This team of scientists in turn directs the Friends of Flax Pond as we recruit community members to participate in the research. Five sites have been selected along the North and South Shore of Long Island to be sampled repeatedly each year. Flax Pond and West Meadow Beach are the sites organized by the Friends of Flax Pond.

Each April, a Training workshop is planned, which is announced in the Times Village Herald and on this website as well as the websites of other environmental groups in our area. At this workshop, Matt Sclafani gives a quick overview of horseshoe crab biology and then describes in detail the method we will use to count the crabs. At the close of the workshop, volunteers are given counting schedules and asked to sign up for the dates they would like to count. Frank Chin and Chris Clotworthy, our Volunteer Organizers, are present at each count to guide volunteers through the process.

The Counting Process

Horseshoe crabs typically spawn from sometime late in May through early July and can easily be seen swimming along the shoreline at this time. Like many other marine species, including fiddler crabs and diamondback terrapins, the lunar cycle drives nesting behavior. On the new moon and the full moon, when tides are at their highest, the largest populations gather to nest. Female crabs can be seen swimming with one or more (smaller) males attached. On most beaches, the female crab comes into the surf zone (where the waves break on the beach) or above it in the sand to dig a nest. She then lays up to 80,000 pale green eggs (each the size of a tiny pellet) while anywhere from one to five or six males attach to her shell and attempt to fertilize the eggs. Each male has a relative chance of fertilizing some eggs, the percentage depending on the part of the female shell where he attaches. She may lay several clutches in a night or over a period of several days. When the tide recedes, shallow indentations can be seen where the nest was dug.

The counting process itself takes little more than an hour once the volunteers have arrived at the site. Counts are taken on three consecutive days at the new moon and the full moon at the night high tide. Exact times vary according to location. Night high tides tend to be later on the North Shore than on the South Shore. It is important to allow enough time to park your car and walk to the site to begin the count exactly at the designated time. Directions are given in advance and a Volunteer Organizer is available by phone to answer questions before as well as during the count. Only volunteers who have been trained and are scheduled ahead of time by the Volunteer Organizer participate in the count. If for any reason, a community member wishes to participate and cannot attend the workshop on the given date and time, call or write the Friends of Flax Pond and arrange a meeting with the Volunteer Organizer, Frank Chin. He can be reached on his cell at 368-0004 or by email: frank.chin@stonybrook.edu