Horseshoe crabs are “living fossils”, the last survivors of a group of organisms that first appeared in the fossil record some 30 million years ago. Delaware Bay has the largest population of horseshoe crabs (Limulus polyphemus) in the world.
Besides their extraordinary antiquity, horseshoe crabs are also of paramount importance to human health. Their blood contains a clotting agent, LAL (Limulus Amoebocyte Lysate), which provides a fast, reliable test for the presence of infections bacteria in drugs, as well as prosthetic devices such as heart valves and hip replacements.
Since 1991, the Wetlands Institute has brought scientists and volunteer citizens together to conduct censuses of the ecologically vital horseshoe crab population on the New Jersey side of the Delaware Bay. These censuses take place during May and June and are central to our understanding and responsible management of this ancient marine creature.
The Horseshoe Crab Conservation Initiative
The Horseshoe Crab (Limulus polyphemus), an important keystone species of the Delaware Bay, is an animal that is very much 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 Horseshoe Crab eggs deposited along the banks of the Delaware Bay for their own nutritional welfare.
As these shorebirds make over a 9,000 mile migration from their wintering grounds along the southern tip of South America to their breeding grounds in the Arctic tundra, they will time their journey so they can take a rest along the shore of the Delaware Bay in order to feast upon said Horseshoe Crab eggs. Shorebirds will spend approximately 2 weeks dining on these eggs in order to double their body weight and regain important energy that is needed to continue with their long journey to the Arctic.
Unfortunately this natural phenomenon is in peril as the number of Horseshoe Crabs in the Delaware Bay has dramatically decreased over time.
In fact, the Delaware Bay’s Horseshoe Crab population has declined by 90% over the last 150 years mostly due to overharvesting by fishermen. 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. The Red Knot has been placed on New Jersey’s Endangered Species list and many other shorebirds are in danger of being placed on that list if horseshoe crab populations are unable to rebound.
In an effort to address the Delaware Bay Horseshoe Crab situation, the Wetlands Institute has embarked on a statewide partnership project to support the stewardship and conservation of Horseshoe Crab populations in New Jersey. As part of this partnership, the Wetlands Institute is taking proactive steps in population restoration as it is utilizing aquaculture techniques in order to help restore local population numbers. During the spring, fertilized Horseshoe Crab eggs are collected from marginal spawning beaches along the Delaware Bay and reared under controlled conditions in our aquarium. After about a month, eggs hatch and newly born Horseshoe Crabs are maintained in their culture tanks. These small crabs are kept in culture tanks until the end of summer or when they are ready to begin feeding. Enclosed in this cultured environment and free of predation, aquaculture dramatically increases Horseshoe Crab survival both before and after the first molts. Come the end of summer, young crabs are released at their respective egg collection locations. In a research experiment initiated by Rutgers University, about 3,000 young crabs will be tagged with coded wire. Some of those crabs will be from the Wetlands Institute. Such tags enable researchers to track crabs and evaluate survival post-release. While most Horseshoe Crabs are released at the end of summer, some remain in the culture systems until release at the end of the following summer. Maintaining juvenile crabs over the winter season allows researchers to further understand protocols for wintering juvenile crabs and evaluate the success of such a tag and release program with older and larger individuals. By raising a number of horseshoe crabs to a juvenile stage of life, the Wetlands Institute and its partners hope to improve the survival rates of juvenile crabs and help increase the population of Horseshoe Crabs in the Delaware Bay.