THE HORSESHOE CRAB IS A FUNDAMENTAL PART OF THE DELAWARE BAY'S ECOLOGY AND IS ESSENTIAL TO THE LIFE CYCLE OF MIGRATORY ShoreBIRDS. we rebuild the beaches so the crabs can reproduce and the birds have places to feed.
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Although the name may suggest otherwise, the horseshoe crab is not a true crab, but rather a member of an ancient group of arthropods that are closely related to spiders and scorpions. Commonly referred to as “living fossils,” horseshoe crabs have remained virtually unchanged for the last 350 million years. Horseshoe crabs, despite looking prehistoric and menacing, are completely harmless. These ancient creatures play a crucial role in the ecology of Delaware Bay, migration of shorebirds, and human health.
The Delaware Bay estuary is the largest stopover for shorebirds in the Atlantic Flyway. Migratory shorebirds, including the threatened Red Knot (Calidris canutus), stop in Delaware Bay each spring to forage and recoup energy before completing their migration north. During this three-week stopover, the birds primarily rely on horseshoe crab eggs that become unearthed from wave action along the Bay beaches. The eggs replenish their fat supply, giving them enough energy to continue their migration to the Canadian Arctic. The American Littoral Society and partners have worked to restore ecologically healthy and resilient habitats along the Atlantic Ocean and within the Delaware Bay region. Creative approaches include sand placement to restore ideal horseshoe crab spawning habitat and the creation of intertidal reefs to protect spawning beaches and shorebird foraging grounds. |
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GEOGRAPHIC RANGE & HABITAT
The Atlantic horseshoe crab population ranges from the Gulf of Maine to the Yucatán Peninsula. Genetic information suggests that there are multiple sub-populations of horseshoe crabs that are divided among larger geographic ranges. Delaware Bay hosts the largest population of spawning Atlantic horseshoe crabs.
In May and June, adult horseshoe crabs in New Jersey line the sandy beaches in shallow bays to spawn and lay eggs. Preferred beach nesting sites consist of porous, coarse-grained sand which allows the sand to be drained and the eggs properly oxygenated. Shallow coves and intertidal sand flats provide protection from intense wave energy during spawning events. Additionally, these areas provide an abundance of food and nursery habitat for juvenile crabs.
During the late summer and fall, adult horseshoe crabs migrate to the continental shelf of the Atlantic Ocean where they will overwinter until the following spawning season.
In May and June, adult horseshoe crabs in New Jersey line the sandy beaches in shallow bays to spawn and lay eggs. Preferred beach nesting sites consist of porous, coarse-grained sand which allows the sand to be drained and the eggs properly oxygenated. Shallow coves and intertidal sand flats provide protection from intense wave energy during spawning events. Additionally, these areas provide an abundance of food and nursery habitat for juvenile crabs.
During the late summer and fall, adult horseshoe crabs migrate to the continental shelf of the Atlantic Ocean where they will overwinter until the following spawning season.
HORSESHOE CRABS & HUMANS
Although there are natural influences on horseshoe crab mortality, horseshoe crabs do face a series of threats from humans. Overharvesting beyond sustainable levels for use as bait in the conch and eel fisheries has put an increase pressure on the population. In the 1990’s, the horseshoe crab population plummeted as a result of overharvesting, which in turn nearly wiped out the migratory shorebird Red Knot (Calidrus canutus), a migratory shorebird, population.
Pharmaceutical companies harvest horseshoe crabs to extract their blood for use in the biomedical industry. Their copper-based blue blood contains amoebocytes which clot when in contact with bacteria. The harvested horseshoe crab blood is used in the biomedical industry to test the presence of bacteria in injectable drugs and medical devices to ensure they are safe for human use. There are growing concerns about the impacts of increasing biomedical harvests on the horseshoe crab population.
As the shoreline becomes more developed, horseshoe crabs have less optimal spawning locations. Bulkheads can sever horseshoe crabs from the intertidal areas and groins can increase the wave energy in spawning areas. The continued loss of suitable spawning habitat will force spawning to sub-optimal areas which may reduce the success of egg development.
Pharmaceutical companies harvest horseshoe crabs to extract their blood for use in the biomedical industry. Their copper-based blue blood contains amoebocytes which clot when in contact with bacteria. The harvested horseshoe crab blood is used in the biomedical industry to test the presence of bacteria in injectable drugs and medical devices to ensure they are safe for human use. There are growing concerns about the impacts of increasing biomedical harvests on the horseshoe crab population.
As the shoreline becomes more developed, horseshoe crabs have less optimal spawning locations. Bulkheads can sever horseshoe crabs from the intertidal areas and groins can increase the wave energy in spawning areas. The continued loss of suitable spawning habitat will force spawning to sub-optimal areas which may reduce the success of egg development.
TAGGING & MONITORING
The community science tagging program grew out of the monitoring plan for the Society-led horseshoe crab spawning habitat restoration efforts along the Bay as a means to gauge the effectiveness of that work. Habitat restoration efforts became an imperative following Hurricane Sandy in October 2012. Beaches along the Delaware Bay that were vital to successful crab spawning were left denuded of sand and covered with debris. This work began in 2013 and continues through today.
It is our hope that through increasing the number of tagged crabs in the Bay we will gain a better understanding of crab movements through each season and year-over-year. This information will also help us identify possible beaches for future restoration projects. Tagging and monitoring data is also shared with the U.S. Fish and Wildlife Service to help inform coastwide policy decisions essential to maintaining healthy populations.
Horseshoe crab tagging takes place in May and June on our restored beaches in Cumberland and Cape May counties along the Delaware Bay and has also expanded to Shark River in Monmouth County. The tagging effort also involves monitoring to help determine how many crabs come ashore for spawning. In addition, our coastal wildlife advocacy initiatives include involvement in counting Red Knots on Delaware Bay beaches, egg-density surveys and a shorebird stewardship program.
Have questions about getting involved? Contact Shane Godshall at [email protected] for more info on Delaware Bay crab tagging. Contact Capt. Al Modjeski at [email protected] for more info on Shark River crab tagging.
It is our hope that through increasing the number of tagged crabs in the Bay we will gain a better understanding of crab movements through each season and year-over-year. This information will also help us identify possible beaches for future restoration projects. Tagging and monitoring data is also shared with the U.S. Fish and Wildlife Service to help inform coastwide policy decisions essential to maintaining healthy populations.
Horseshoe crab tagging takes place in May and June on our restored beaches in Cumberland and Cape May counties along the Delaware Bay and has also expanded to Shark River in Monmouth County. The tagging effort also involves monitoring to help determine how many crabs come ashore for spawning. In addition, our coastal wildlife advocacy initiatives include involvement in counting Red Knots on Delaware Bay beaches, egg-density surveys and a shorebird stewardship program.
Have questions about getting involved? Contact Shane Godshall at [email protected] for more info on Delaware Bay crab tagging. Contact Capt. Al Modjeski at [email protected] for more info on Shark River crab tagging.
