There aren’t too many critters that have roots dating back to 440+ 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 their extensive history surviving through multiple mass extinction events, need our help now more than ever. These “crabs” are not crabs at all but arthropods belonging to the subphylum Chelicerata which contain members like spiders and scorpions but don’t worry; the spiked tail of the horseshoe crab called the telson is harmless and if used to right themselves if tipped over. The Atlantic horseshoe crab can be spotted from Maine to Mexico bouncing around the bottom miles offshore up to the shoreline but prefer shallower, more estuarine environments where they eat a wide range of items, including mollusks, crustaceans, worms, and algae. Horseshoe crabs can live up to 15-20 years and molt 16-17 times in their lives and don’t reach reproductive size until 9-10 years in age!
But why should we care about this cool looking creature? These primitive organisms are of great value to both 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 which help feed a variety of organisms including threatened shorebird species. Due to development and hardening of our shorelines, areas where horseshoe crabs historically nested may not be accessible for them to use, impacting both the crabs and the species that rely on them. Have you ever had surgery or vaccination? Then you were positively impacted by a horseshoe crab! 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.
In 2015, the Florida Fish and Wildlife Research Institute (FWRI) and the University of Florida Launched the Florida Horseshoe Crab Watch, which is a citizen science initiative where trained volunteers help scientists with surveying, tagging, and resighting our state’s nesting populations. Beach nesting surveys happen each spring (March-April) and Fall (October-September) new and full moon high tides when spawning activity should be the highest. 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. More information can be found about the program online including a virtual volunteer training. Local Florida Horseshoe Crab Watch program coordinators also hold in person workshops in their respective counties and here in Collier/Lee we conduct them in the Fall. We have 2 sites in Collier and 2 sites in Lee County we survey each season and are always looking for dedicated volunteers.
Michael Sipos is the Florida Sea Grant agent for UF/IFAS Extension Collier County. Contact him at sipos624@ufl.edu. For more marine educational content and updates on upcoming programs, check out linktr.ee/CollierSeaGrant.
