MERRITT ISLAND, Fla. – On a windy morning at Kelly Park East, a small group of volunteers fan out along the shoreline, clipboards and buckets in hand, eyes scanning the surf for one of nature’s oldest survivors.
They’re part of the Florida Horseshoe Crab Watch, a statewide citizen science initiative that turns everyday Floridians into frontline researchers for a species that has roamed Earth’s oceans for hundreds of millions of years.
Holly Abeels, a Florida Sea Grant Extension Agent with the University of Florida IFAS Extension in Brevard County, helps lead the effort.
She says the program was designed to bring structure to what had previously been an informal, unreliable process.
“In the past, what they would rely on would be just people seeing them,” Abeels said. “They would say, ' Hey, I saw horseshoe crabs, and then report that into a spreadsheet or a form. So that was how they would do it before — it was kind of haphazard.”
The program, which has been running statewide since 2015, uses trained volunteers to survey designated sites during specific tidal and wind conditions.
Volunteers head out around the new and full moon at high tide — or, in Brevard County’s case, when strong onshore winds mimic tidal conditions in the largely tide-free Indian River Lagoon.
“We time them for what would normally be the high tide,” Abeels explained. “But we also time them for wind surveys. Around the rest of the state, they just do tide surveys.”
The surveys aren’t just for curiosity’s sake. Horseshoe crabs, which are not really crabs but are more closely related to spiders, play a critical role in the biomedical industry — and in human health.
“The biomedical industry, they actually collect horseshoe crabs and they take a third of their blood,” Abeels said. “And they use that blood in the medical industry to test for gram-negative bacteria on any products that might go into humans.”
The test, known as The Limulus Amebocyte Lysate (LAL) test uses the copper-based blue blood of Atlantic horseshoe crabs to detect bacterial endotoxins in pharmaceutical products, vaccines and medical devices.
Amebocytes in the blood clot instantly upon exposure to endotoxins, providing an ultra-sensitive, reliable safety check.
It’s a multi-million dollar industry — and it depends on a healthy horseshoe crab population.
“If you’ve ever gotten a vaccine, if you’ve ever had some type of device implanted into you, all of that has to be tested,” Abeels said. “And so the test comes from horseshoe crabs.”
Beyond biomedical uses, horseshoe crabs also support an aquarium trade and are used as bait in the eel fishery. Their eggs are a major food source for migrating shorebirds.
“The horseshoe crabs in our part of the world, in Brevard County specifically, like to come up when the wind is blowing onshore,” Abeels said. “It’s usually around 15 miles per hour. Sometimes it can be a little bit less, but usually around that for a couple of hours — and that sort of pushes the water high enough to kind of mimic high tide.”
Abeels’ team has two primary survey sites in Brevard County: Kelly Park in Merritt Island and Parrish Park in Titusville. The Parrish Park site, she says, is one of the most productive in the state.
“The Parrish Park site has one of the highest numbers of horseshoe crabs in the state,” she said. “We see thousands of horseshoe crabs potentially on a really good wind survey day.”
When horseshoe crabs do appear, the work begins in earnest. Volunteers like Lacey Homan, a longtime survey participant, carefully collect crabs, keep mated pairs together, and take a detailed set of measurements before releasing them.
“We start at a specific time and walk the same amount of beach every time,” Homan said. “We’re looking and scanning for any horseshoe crabs that have come up to nest. And as we find them, we’ll mark down what kind they are — whether it was a male or a female, or if it was a nesting group.”
Tags come from the U.S. Fish and Wildlife Service as part of a national mark-recapture program. Volunteers record weight, carapace length, estimated age — young, medium, or old — and condition of each crab. All data flows to the Florida Fish and Wildlife Conservation Commission database and ultimately into an annual statewide report.
“This is all done by volunteers,” Abeels noted. “They get trained to do this, and as you can see, they have a very strict protocol. They know exactly what they’re doing.”
The tagging program has already yielded remarkable results. During an acoustic tagging study in Titusville, one tracked female traveled roughly 15 miles south through the Indian River Lagoon — and then returned to the same nesting area the following year.
So far, Brevard County’s horseshoe crab numbers appear stable. The surveys have been conducted every year since 2019, and crabs have shown up consistently each season — a hopeful sign for a species that has survived largely unchanged for hundreds of millions of years.
“We’ve been doing this since 2019, so it hasn’t been very long if you think of science being long-term,” Abeels said. “But pretty steadily, we do see several hundred to several thousand every time we survey. So we have a good population here in Brevard.”
Still, Abeels points to one growing concern: the loss of sandy shoreline. Horseshoe crabs, like sea turtles, must come ashore to lay their eggs — and “armored” shorelines lined with rocks or seawalls block their access.
“There are certainly places where they can’t go anymore,” she said. “So we have a lot of places that are armored along the shoreline, and so there’s sort of a limited number of places where they have that ability to do that.”
Brevard County surveys run from February through April.
Anyone who spots a tagged horseshoe crab is encouraged to report it to the U.S. Fish and Wildlife Service.