Project investigates why horseshoe crabs dwindling in state

NORWALK — When sisters Heather and Jennifer Bellizza first moved into a house on the Stamford shore in 2003, they were careful venturing out with their inflatable rafts — they didn’t want to pop one on the spiky, armored creatures that have roamed the shores for 450 million years.

Horseshoe crabs thrived on Connecticut’s beaches, sometimes in such numbers it was hard to pick your way through them.

“There were two weekends when you couldn’t get in the water — it was just horseshoe crabs,” Heather Bellizza said.

“We want to know what’s going on in Connecticut.”

David Hudson, Maritime Aquarium staff scientist

By the time they moved a decade later, the numbers had dipped, and, on Thursday night, the Bellizzas gathered at the Maritime Aquarium with five dozen citizen scientists of all ages to help professional scientists figure out why.

Over the upcoming months, the group will go out to Calf Pasture Beach to tag the prehistoric crabs swarming the shores for mating season. The data will be logged as part of Project Limulus, a Connecticut horseshoe crab census.

“It’s the most wonderful time of the year,” said Bridget Cervero, the aquarium educator supervisor, as she prepared to guide the citizen scientists through the process of tagging the crabs.

Horseshoe crab eggs are essential for the Sound’s ecosystem — “This is essentially the Powerbar of these migratory birds” — and the crabs themselves support the fishing industry — “They’re used as bait for eels and whelks.”

And their milky blue blood is invaluable in medicine. “It’s a major way we prevent cases of meningitis” said Staff Scientist David Hudson.

As horseshoe crabs grow, they outgrow their exoskeletons and shed them, leaving behind a complete shell of what they once were. The trick to distinguishing a dead crab from a shell is the smell, staff explained. Either way, if you find one with a plastic tag, follow its instructions to report the finding, they said.

The crabs are thought to live up to four decades and reach sexual maturity at around 10 years old. However, adolescent crabs have become a rare site in the state.

“We’re not seeing this size,” Hudson said, referring to crabs smaller than the palm of one’s hand. “They’re really prevalent on the Cape, they’re really prevalent in Rhode Island — we want to know what’s going on in Connecticut.”

In their quest to gather data that could answer that question, volunteers learned how to record the tag number and date, how to hold a crab while measuring its width, and how to differentiate a male from a female (the secret is the shape of their front claws). In addition, horseshoe crabs can form chains while mating, so citizen scientists were asked to record the number of crabs in the chain they were measuring. Cervero assured those worried about disrupting them that “they come right back together.” For the actual tagging, an awl was used to pierce the shell of the horseshoe crab, made of the same material as human fingernails.

When staff came around to each table with live horseshoe crabs, they flipped them over and cradled the crabs’ shell like a bowl, so the undulating legs pointed toward the ceiling. Where the legs came together was a bristling hole, the crab’s mouth, which eats what is underneath it. While the animals are called crabs, they’re actually more closely related to spiders or scorpions. Like arachnids, the horseshoe crab has multiple sets of eyes that detect different things, and, just as a spider has lungs that resemble the pages of a book, the horseshoe crab has what are known as book gills, overlapping plates beneath its tail.

Jennifer’s daughter, Francesca Bellizza, a dinosaur fan and owner of a fossilized specimen of the horseshoe crab’s ancestor, the trilobite, peered closely at the horseshoe crab brought to her table. “I’m excited,” she said of the prospect of searching for the living remnants of the Paleozoic Era at 11 p.m. on a weekday (horseshoe crab breeding is more active at high tide and at night).

David DaSilva, whose family drove from upstate New York for the training, felt the shell of a horseshoe crab as it flexed its pronglike tail — a telson — up and down.

“It felt like sometimes when you touch a snail — smooth and slightly wet,” he said.

As the training wrapped up, Hudson thanked the volunteers for helping with the census.

“The work you do today will be seen a decade from now,” he said.

Alex von Kleydorff / Hearst Connecticut Media Maritime Aquarium Educator Devan Shulby shows a horseshoe crab up close.

Alex von Kleydorff / Hearst Connecticut Media Bridget Cervero, citizen science coordinator for the Maritime Aquarium, shows where the tag goes on a horeshoe crab to Luke Vivano, 7, and his dad, David, during a volunteer orientation on Thursday in Norwalk.