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If you see horseshoe crabs having some "private time" take notes

DEP Florida Horseshoe crabs from FWD.jpg
Florida Fish and Wildlife Conservation Commission
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Horseshoe crabs mate in the surf zone during the spring and fall in Florida

If you’re walking the beach and happen along a pair of horseshoe crabs linked together at water’s edge, and they are sort of wiggling about in the sand, you probably want to leave the couple alone as they are having some "private time."

However, the Florida Fish and Wildlife Conservation Commission would appreciate it if you took some notes.

The Florida Horseshoe Crab Watch Program is a citizen-scientist initiative to collect data throughout the state. Reporting horseshoe crab sightings provides valuable information about habitat use, population distribution and environmental conditions for nesting to the FWC. Although horseshoe crabs have existed for more than 450 million years, scientists are still learning about Florida's population.

"Horseshoe crabs are extremely important ecologically. They play a significant role in the ecosystem," said Armando Ubeda, a scientist with Florida Sea Grant. "So since we don’t know how the population in Florida are doing that’s the reason we want to inventory them because they are an important component of the ecosystem and they are extremely valuable for society."

With spring a few weeks away it’s nearly peak mating season for horseshoe crabs. They mate by pairing up, with the smaller male attached to the larger female. They then crawl onto the beach up to the high-tide line where the female digs a nest and lays her eggs, all while the male is attached and fertilizing them.

They mate year-round but it is most common to see mating groups along the shore of sandy, low-wave action beaches in March and April, as well as September and October. Beachgoers will have the most luck spotting horseshoe crabs around high tide within a few days of a new or full moon. The information volunteers collect about the ancient creatures is reported online.

A horseshoe crab has ten “eyes” spread around its body, two of the conventional type, some that see ultra-violate light, and others it uses to stay oriented when swimming.

“They've been around for 450 million years, which means they watched the rise and fall of millions of other species, and survived ice ages,” Katie Pavid wrote for the National History Museum last year. “These crabs may look prehistoric, but they do an important job of supporting other animals around them: their eggs are a nourishing snack for migrating birds. They are also good for fishermen because they help keep the sediment around coastlines healthy.”

Ubeda, of Florida Sea Grant, said the blood from horseshoe crabs is rich in copper and is drawn to make products that detects bacteria in medical uses, including keeping humans healthy.

"Horseshoe crabs, and the way they protect themselves, you know, when they get caught and things like that, the blood coagulates and that is when the detect things that shouldn’t be there like bacteria," he said. "So we use their blood to detect some kind of containment in medical equipment or medicines that we use like vaccines we develop. We test them with horseshoe crab blood to see if it is free of any kind of containment.

Horseshoe crabs were hanging out on the planet before nature decided to find out whether dinosaurs would be a good fit, too, and the crabs remained long after that experiment failed. Anyone who has watched any of the movies of the “Alien” series knows Hollywood special effects folks could have used a horseshoe crab as a stand-in for the alien’s face-hugging, host-seeking, baby-alien-injecting creature.

And despite having "crab" in its name, the animal is an arthropod, or a sort of arachnid. In fact, horseshoe grab are closely related to the extinct sea scorpion.

Data gathered during last year’s horseshoe crab count included 720 unique sampling events across 38 sites with a total of 85,413 crabs counted, 3,301 crabs tagged, and 269 crabs moved to safer areas. The county with the largest number of crabs observed during the spring season was Brevard with 73,709 crabs counted. Last fall, Pasco County’s volunteers saw the largest number of crabs with 1,405 counted.

In Sarasota County last year, the average size of a female horseshoe crab was just over two pounds and about 7 inches, while males weighed about 11 ounces and were a just over 5 inches wide. In Lee County, the average sized female weighed just under three pounds and was about 8 inches wide. Males in the county weighed just under a pound and were about 5.5 inches wide. In Charlotte County, only female crabs were spotted and they were small, weighing about 10 ounces and just over 5 inches wide. Volunteers did not find any horseshoe crab on Collier County beaches during survey days.

Statewide, the average female horseshoe crab weighs just under three pounds and are about eight inches wide, while males weigh about a pound and are about six-and-a-half- inches wide.

If you see a horseshoe crab on its back, you can help it flip back over by gently picking it up while holding both sides of the shell, turning it over and releasing it back into the water. Simple actions such as this help conserve this species and the many other species that depend on it.

To volunteer with the state's horseshoe crab counting program, click here.

The FWC asks the public to report horseshoe crab sightings by visiting MyFWC.com/research , clicking on “crustaceans,” then “horseshoe crabs,” and selecting “Report Your Nesting Horseshoe Crab Sighting.”

Environmental reporting for WGCU is funded in part by VoLo Foundation, a non-profit with a mission to accelerate change and global impact by supporting science-based climate solutions, enhancing education, and improving health.