Horseshoe Crabs Reveal Egg Development on Coastal Beaches

Horseshoe crabs are drawing attention along the Mid-Atlantic Coast and Delaware Bay as females return to sandy beaches to lay eggs that become transparent during development, according to The Dodo. The seasonal spawning process allows developing baby crabs to be observed before hatching.

The animals spend most of their lives in deeper ocean waters and move toward beaches during full or new moons when higher tides help them reach spawning areas, according to The Dodo.

Sheila Eyler, project leader of the Mid-Atlantic Fish and Wildlife Conservation Office for the U.S. Fish and Wildlife Service, said female horseshoe crabs create nests in sand and deposit thousands of eggs during repeated visits to beaches.

"When it’s time to spawn, they all make this mass movement toward beaches and they spawn on sandy beaches — that’s where they like to lay their eggs," said Sheila Eyler, project leader of the Mid-Atlantic Fish and Wildlife Conservation Office for the U.S. Fish and Wildlife Service.

According to the U.S. Fish and Wildlife Service, each nest can hold up to 4,000 eggs. The eggs develop from small green pellets into translucent spheres during a two- to four-week incubation period.

"She can lay up to 100,000 eggs over the course of one season," said Sheila Eyler, project leader of the Mid-Atlantic Fish and Wildlife Conservation Office for the U.S. Fish and Wildlife Service.

After hatching, young horseshoe crabs survive without parental care and require about 10 years to reach reproductive maturity, according to the U.S. Fish and Wildlife Service.

Eyler described horseshoe crabs as an ancient species that has remained largely unchanged for hundreds of millions of years. The animals are often called living fossils, and three of the world’s four horseshoe crab species are considered endangered.

"They are an ancient critter. They haven’t really changed … for 350 million years. So they were around during the time of the dinosaurs, basically like they look today," said Sheila Eyler, project leader of the Mid-Atlantic Fish and Wildlife Conservation Office for the U.S. Fish and Wildlife Service.