If you’ve ever had an injection, vaccination or surgery, you’ve benefited from the mysterious creature known as the American horseshoe crab.
In the 1950s, Frederick Bank discovered that the special cells in the horseshoe crab’s blue blood prevent bacteria from invading the animal’s body. The animal’s unique copper-based blood contains a substance called Limulus Amebocyte Lysate, or LAL, which coagulates in the presence of small amounts of bacterial toxins.
The LAL is used to test the sterility of medical equipment and virtually all injectable drugs. Scientists quickly put that information to work for the biomedical industry.
Because of their value to the medical field, and their eggs being a major food source for fish and bird species — as well as prey for sea turtles, alligators, horse conchs and sharks — there is some debate as to what those impacts are having on the population.
Efforts have stepped up in recent years to try to identify spawning areas along the Atlantic Coast. Some organizations say horseshoe crabs are declining, while others argue they are stabilizing.
Florida lags behind even though the Florida Fish and Wildlife Conservation Commission launched a similar effort in 2015.
The mid-Atlantic states began in the late 1990s.
“Florida is a big unknown when it comes to how the population is doing overall,” said Clair Crowley, FWC crustacean fisheries biologist. “We lack long-term data on the species, which is necessary to have when you want to examine a long-lived species, such as horseshoe crabs. The development of the Florida Horseshoe Crab Watch has increased our statewide surveys of the spawning population, and we hope to have a better understanding of increases or declines in the population over the next few years.”
FWC can’t do it alone, however, and is relying on the public for help in identifying spawning areas. Crowley said the animals are most likely to spawn on sandy, low-wave-action beaches.
“In Manatee County specifically, we have had reports from Robinson Preserve, around the Skyway Bridge and in Palma Sola Bay,” Crowley said. “In the right location, you can expect to see them in larger numbers during the new and full moons at high tide.”
The FWC does not have specific horseshoe crab population numbers for the Florida Keys, but Crowley said she hopes to start monitoring there “in the near future.”
“In the Keys, it is the juveniles that are normally harvested, as they are easy to spot in seagrass flats and shallow waters. The adults will occupy these areas, but also move offshore,” Crowley said.
Larger horseshoe crab populations are found in other parts of the state like the Big Bend area of the Panhandle and Indian River Lagoon in the central Atlantic part of the state, she said. People in these areas typically see the crabs when they come up on the beach to spawn, usually on full and new moons and high tides.
“With the amount of shoreline development we see today, they will try and spawn at just about any sandy spit they can find,” Crowley said.
It’s not really a crab
There are four species of the horseshoe crab, but only one exists in North America ranging from Maine to Florida. All three of the remaining species exist in Southeast Asia.
They also aren’t crabs and are more closely related to spiders and other arachnids. They contain little meat for consumption, perhaps a benefit to their population, though anglers do harvest them for bait.
The horseshoe crab is often called a “living fossil,” because they have existed nearly unchanged for 445 million years, predating the dinosaurs by hundreds of millions of years, surviving all five of the known mass extinction events.
They may look a little scary from their ancient appearance but are harmless. They have sharp tails, which are designed to help them flip themselves over if turned over by a wave or while crawling through the mangroves. A horseshoe crab has 10 eyes, so they are sensitive to light. They have two primary eyes but also “photo receptors” in other areas, primarily along the tail.
If you see a horseshoe crab turned over, never pick it up by the tail or the animal could be severely injured. Always use two hands, grab each side of its exoskeleton body and flip it over.
Determining they are mating to help report a potential spawning area is fairly simple. The male and female will attach to one another and group mating is not uncommon. The female lays the eggs in the sand and juvenile horseshoe crabs look just like the adults, only smaller. They shed their exoskeletons up to 17 times in their 20-year lifespan so seeing a “skeleton” on the beach or in the mangroves doesn’t mean it was killed.
Information on how to report a potential horseshoe crab spawning area can be found at fwc.com or call 866-252-9326.
The future for horseshoe crabs
The animal’s value stock continues to soar, making its preservation more important than ever. Additional research also is leading to a better understanding of human vision. NASA is now testing LAL in space to assist in the diagnosis of astronauts.
The Horseshoe Crab Conservation of Charles River in South Carolina is one organization saying the population there is stable if not increasing. They claim that’s possible because of the research they do. They hand harvest the blood and return the animals to their natural habitat that same day and use just 1/20th of the LAL needed for traditional testing through its own technology.
That means fewer donors are needed and the organization claims that if everyone followed their lead, “The worldwide demand could be met with the blood collected from our biannual quota of donors without needing to bleed a single extra crab,” according to its website.
For now, Florida is playing catch-up, but making progress considering the Sunshine State boats significantly more miles of coastline than other states.
“Public reports help us identify beaches that are crucial for spawning horseshoe crabs,” Crowley said. “Florida has many miles of coastline, making it difficult to survey without the public’s help. Once we identify spawning beaches, we can conduct more regular surveys and tagging through our Florida Horseshoe Crab Watch program to understand population dynamics, movement and other important questions we have about horseshoe crabs.”
Crowley said part of the tagging program “will help us understand movements within estuaries and along the coast. Currently, our work shows that the majority of crabs return to the same beach or one nearby during the spawning season.
“However, crabs have been recorded traveling over 50 miles, much further than we previously thought.”