CHARLESTON COUNTY, S.C. (WCBD) – Biologists with the South Carolina Department of Natural Resources say horseshoe crab eggs and hatchlings can survive in a ‘surprisingly different’ environment – the salt marsh.

Horseshoe crabs come ashore en masse each spring to mate and lay eggs on sandy beaches, which have long been considered the best and possibly only environment where horseshoe crab eggs can successfully hatch and grow.

“We’ve known for a long time that horseshoe crabs spawn in the salt marsh, but we thought those eggs didn’t survive the low-oxygen environment of pluff mud,” said assistant scientist Dr. Michael Kendrick, who leads horseshoe crab research at SCDNR.

Dr. Kendrick said the adaptability of the horseshoe crabs to “successfully reproduce in a wide range of habitat types” highlights one of the reasons why the group of animals has existed on the planet for more than 480 million years.

SCDNR says “the American horseshoe crab is an ancient marine invertebrate recognized by its pointed tail and domed ‘head,’ which protects six pairs of walking and feeding feet. Although they spend much of their lives offshore feeding on small clams and worms on the seafloor, they’re not uncommon on South Carolina beaches – particularly when they come ashore under new and full moons to mate and lay eggs during the spring.”

The species plays a critical role in the coastal ecosystem and human health.

SCDNR officials say their eggs are important food sources for tens of thousands of shorebirds making long migrations, and a compound in their blood is collected and used to detect contamination in vaccines and medical devices.

Horseshoe crab eggs (center) in the pluff mud of a salt marsh (Photo: SCDNR/Crustacean Management and Research Section)

Horseshoe crab numbers have declined in places like New York, but a recent study by the Atlantic States Marine Fisheries Commission found the Southeast’s horseshoe crab population to be in “good” condition.

As coastal South Carolina grows and changes, biologists will monitor where the crabs are spawning, how many there are, and the state of their genetic health.

Dr. Kendrick says the findings have changed the way his team thinks about the importance of the salt marsh to the animals they study.

Horseshoe crab season is underway. You can help SCDNR biologists better understand the crabs by reporting sightings with photos to