Survivors of Time: Why Horseshoe Crabs Matter More Than You Think
Something remarkable occurs each spring along the South Jersey shore. Under the glow of the moon, thousands of horseshoe crabs crawl onto the sandy beach in one of the largest spawning events on Earth. It’s a scene that feels almost prehistoric, and in many ways, is.
“Horseshoe crabs are basically marine ancient arthropods. They’re often mistaken for crustaceans, but they are more closely related to modern-day spiders and scorpions,” Danielle Dyson, a fisheries biologist with the New Jersey Department of Environmental Protection’s Department of Fish and Wildlife. “They’ve been around for about 450 million years, survived multiple mass extinctions and basically had very little change.”
This history is why the domed, armor shelled creatures with the spiked tail are often referred to as “living fossils.” But beneath the intimidating exterior lies an ecologically vital species that plays a crucial role in coastal life. Each year migratory shorebirds, particularly the red knot, travel thousands of miles from South America to the Arctic, stopping along the Delaware Bay to refuel, according to Danielle.
“They are super important in ecosystems because they are a cornerstone to the coastal food web,” Danielle said. “Without horseshoe crabs, those shorebird species would struggle to survive those long-distance migrations.” Beyond their role as egg-layers, horseshoe crabs also contribute to the health of the ocean floor, feeding on worms, mollusks and other decaying organic matter. Spawning takes place anywhere from late April through June, especially around full and new moons, but observant beachgoers may still spot them outside of that window. “You could see them washed up on any of the beaches on the ocean side,” Danielle said. Early morning walkers may spot a lone crab tracing a line along the wet sand, or the distinct outline of a shell left behind by the tide. These quiet encounters offer a reminder that even outside of peak spawning zones, the Jersey Shore’s beaches remain connected to the larger coastal system that sustains the species.
If you encounter a horseshoe crab during your beach walk, the best advice is simple: admire, but don’t interfere. “Horseshoe crabs are a protected species, so if you do come across one on the beach, it is in the best interest to leave it alone,” Danielle said.
However, there is one exception to this sage advice: if you find a crab flipped upside down, a vulnerable
position that could be fatal, you can gently help.
“If you see it flipped upside down, you can gently pick it up by the sides of the shell, not the tail,” Danielle explained. “If you pick it up by the tail, that could be a
bit of an issue for them.”
Some horseshoe crabs may be bearing small tags, which can be reported to the agency listed on the tag for research purposes.
Like many marine species, horseshoe crabs have faced significant challenges. Decades ago, overharvesting for fishing bait and biomedical use caused dramatic
population declines, along with impacts on shorebird populations.
“Before the nineties, horseshoe crabs were not monitored as closely and we saw massive declines in their populations, which also had massive declines for some of the shorebird populations,” Danielle said. “Here in New Jersey, we have a total moratorium on harvest, so we do not allow harvest for commercial bait.”
Additionally, habitat loss and climate change add further uncertainty.
“They depend on those sandy intertidal beaches, so coastal development can really reduce available spawning habitat,” Danielle said. “If we’re adding bulkheads and sea walls or dredging, we can see a loss of suitable beaches.”
Climate change, specifically stronger storms, can erode beaches faster than they can naturally rebuild, washing away eggs before they hatch or altering the slope of the shoreline in ways that make spawning more difficult.
New Jersey has joined other Mid-Atlantic states in conservation efforts, and the Delaware Bay horseshoe crab population is currently considered “stable to improving,” according to Danielle.
“We’ve seen it grow substantially, and we’re seeing coastwide abundance in recent years.”
One of the most surprising facts about horseshoe crabs lies not on the beach, but in scientific labs. Their bright blue blood plays a critical role in modern medicine. It contains a substance called limulus amebocyte lysate, or LAL, which is used in vaccines, injectable drugs and medical devices.
“When it comes into contact with bacteria it clots almost immediately,” Danielle said. “Scientists can use this reaction as a high sensitivity test.”
For those inspired to do more than observe, there are ways to help in conservation efforts.
“If you ever notice something out of the ordinary, you can report that through the conservation reporting form on the Fish and Wildlife website,” Danielle said.
Volunteer opportunities also exist through regional spawning surveys.
Whether you are a year-round resident or a summer visitor, the horseshoe crab is a reminder that the Jersey Shore’s beaches are more than a place to relax – they’re part of a living, ancient ecosystem still thriving today.
By Rebecca L. Forand. Photos courtesy of NJDEP.