by Shelby Schmeltzle
The Atlantic Horseshoe Crab (Limulus polyphemus) is an important keystone species of the Delaware Bay. As such, the horseshoe crab is depended upon by many other species participating in the ecosystem. Shorebirds such as the Red Knot (Calidris canutus), Ruddy Turnstone (Arenaria interpres), and the Sanderling (Calidris alba) depend upon the horseshoe crab’s tiny, green, protein-rich eggs deposited along the banks of the Delaware Bay for their own nutritional welfare. Some of these shorebirds make a 9,000 mile migration from their wintering grounds along the southern tip of South America to their breeding grounds in the Arctic tundra. Their journey is timed so they can take a rest along the shore of the Delaware Bay in order to feast upon this large concentration of horseshoe crab eggs. Unfortunately, the Delaware Bay’s horseshoe crab population has declined by 90% over the last 15 years mostly due to overharvesting and habitat degradation. As the number of horseshoe crabs have decreased, so have the number of eggs available for consumption by migrating shorebirds. Shorebird population numbers are therefore plummeting as well, as many cannot gain the amount of energy needed to complete their migrations.
In an effort to address the Delaware Bay horseshoe crab situation, with proper permitting, The Wetlands Institute (TWI) collects fertilized horseshoe crab eggs from spawning beaches along the Delaware Bay and rears the eggs under controlled conditions in our aquarium. After about a month, eggs hatch and newly born horseshoe crabs are maintained in their specially designed culture tanks consisting of two large chambers with netted lids that keep eggs inside the chambers while allowing them to receive oxygenated seawater and prevent unwanted fungal growth. The lower part of the system contains fine-medium grain sand where larger hatchlings reside for public viewing. Enclosed in this cultured environment and free of predation, aquaculture dramatically increases horseshoe crab survival both before and after the first molts. These small crabs are kept in culture tanks until they are ready to begin feeding. From there, some are released at their respective egg collection locations and others enroll in the Horseshoe Crabs in the Classroom program, which is a joint initiative between TWI and the NJ Division of Fish and Wildlife’s Aquatic Education program. This program allows teachers across New Jersey to raise horseshoe crab hatchlings in specialized tanks in their classrooms. In only its second year, the program currently has eight participating teachers, each taking approximately 25 horseshoe crab hatchlings and 25 fertilized eggs, resulting in approximately 400 horseshoe crabs going into classrooms throughout New Jersey, more than doubling efforts from the first year. In the coming weeks, the teachers will return their grown horseshoe crabs to TWI so we can release them back into their natural habitat.
Want to join in a horseshoe crab release, learn more about the Horseshoe Crabs in the Classroom program or see the horseshoe crab hatchery display? Then come on over to The Wetlands Institute every Thursday evening for Horseshoe Crab Mania Thursday where our educators give presentations focusing on horseshoe crabs, their conservation, and we release one of our larger horseshoe crab hatchlings. We look forward to seeing you!
