Tails as Old as Time!

There aren’t too many critters that have roots dating back to 440-plus million years ago that are still around today, but one estuarine inhabitant that you may frequently walk past while visiting the coast has been scootering around our shorelines before the dinosaurs first appeared. 

This critter is the Atlantic horseshoe crab (Limulus polyphemus), and despite its extensive history of surviving through multiple mass-extinction events, it needs our help now more than ever. There are four species of horseshoe crab worldwide, with only one species in the Atlantic. The others inhabit coastal waters in Asia. 

Have I piqued your interest? Would you like to know more about horseshoe crabs?

Local Florida Horseshoe Crab Watch program coordinators hold in-person workshops in their respective counties. The next one is at North Collier Park from 9:00 AM to 12:00 Noon, August 11th. Registration and more information about the program can be found by visiting www.bit.ly/FLHSC. 

Now, let me tell you more about these “crabs.” They’re not crabs at all but arthropods belonging to the subphylum Chelicerata. This subphylum includes members like spiders and scorpions but don’t worry; the spiked tail of the horseshoe crab -- called the telson -- is harmless and is used to right themselves if tipped over.

You can see the Atlantic horseshoe crab from Maine to Mexico, bouncing around the bottom, miles offshore - up to the shoreline, but they prefer more shallow estuarine environments, where they eat a wide range of items including mollusks, crustaceans, worms and algae. 

Horseshoe crabs can live up to 20 years and molt 16 to 17 times in their lives and don’t reach reproductive size until they’re nine to -10 years old.

But why should we care about this cool-looking creature? 

To start with, they provide great value to humans and the environment. Horseshoe crabs and their eggs are important to coastal food webs and ecosystems.

These crabs gather in large nesting aggregations on shorelines, where a single female can lay up to 60,000 eggs, buried in moist sand. These eggs help feed a variety of organisms, including threatened shorebird species. 

Because of the development and hardening of our shorelines, areas where horseshoe crabs historically nested may not be accessible for them to use. This impacts the crabs and the species that rely on them. 

Have you ever had surgery or a vaccination? Then a horseshoe crab helped you. The blood of the horseshoe crab contains limulus amebocyte lysate, or LAL, which is extracted and used by the biomedical industry. When LAL is exposed to bacterial endotoxins, the mixture begins to clump and is used to test the sterility of medical equipment and nearly all injectable drugs to prevent the risk of infection. 

There are additional uses for these crabs. including bait for whelk fisheries elsewhere on the globe and harvest for the aquarium trade. 

In 2015, the Florida Fish and Wildlife Research Institute (FWRI) and the University of Florida launched the Florida Horseshoe Crab Watch. This is a citizen science initiative in which trained volunteers help scientists with surveying, tagging and resighting our state’s nesting populations. This program is a great way to help both the horseshoe crab and scientists keep tabs on how our crabs are doing while giving volunteers a great excuse to learn more about an important coastal critter and take some walks on the beach.