If you are a regular beachcomber along Southwest Florida’s coast, it’s quite likely you’ve seen a strange creature known as the horseshoe crab. Fossils show us that horseshoe crabs have not changed in 400 million years. Not technically a crab (actually a closer relative to spiders and scorpions), this ancient animal is a valuable partner in cutting-edge modern medicine.
Horseshoe crabs are found along the Atlantic coastline from Maine to the west coast of Florida. They generally remain underwater and out of sight until breeding season. During spring and fall new and full moons, horseshoe crabs with one thing on their mind find mates in the surf at the high water line.
Females, which are much larger than males (think dinner plate versus saucer), bury themselves in the sand. The smaller males lock on from behind. Although they’re aquatic creatures, they can remain out of water for days as long as their gills remain moist.
Other male crabs will congregate around the female as eggs are laid, producing sperm and increasing the chances for plentiful progeny. Two to four weeks later, the eggs hatch and the larvae swim to the water. If they survive, they’ll molt into juvenile form a few weeks later. Horseshoe crabs can live around 20 years and reach sexual maturity after roughly nine years.
When thinking of crabs, it’s natural to assume their appendages are to be avoided, but these guys don’t have pincers of any consequence. Each leg ends in a claw, but they’re not strong and are primarily used to push themselves along the sea bottom. Males have specially adapted small pincer to attach to females during mating season.
One of the really interesting facts about the horseshoe crab is that its blood is copper-based, giving it a bluish color. This blood contains an agent (limulus amebocyte lysate) that is extremely sensitive to coagulation and thus invaluable to medical research. Pacemakers, implants, and even vaccines like that for COVID have been tested with the blood from horseshoe crabs.
This resource is renewable. Blood is drawn from crabs that are caught just for this purpose and then released afterward. However, this is not currently done in Florida. But the Florida Fish and Wildlife Conservation Commission does have an interest in monitoring the population, which is where the Florida Horseshoe Crab Watch comes in.
There is a dedicated group of volunteers around Florida willing to count, measure and tag horseshoe crabs found during breeding season. Unfortunately, red tide has affected horseshoes as it has other sea creatures, and our group in Charlotte County has had tough luck finding live ones.
If WaterLine readers encounter live horseshoe crabs, it would be helpful if you would report them. Go to the survey page at https://bit.ly/2Y2teq2. The online form is easy to use and helps FWC with data collection. Please report only live crabs, not dead ones or molted shells.
Additionally, you might see a horseshoe crab with a tag attached on the left side of its carapace, or shell. Take a picture of the tag and report it to the FWC via the phone number on the tag. Any tagged crab, dead or alive, should be reported.
Every person reading this column knows that we need clean water, and live horseshoe crabs are evidence of just that. The data we collect — all of us — helps FWC and, indirectly, the medical research community. That’s why I’ve learned to love our prehistoric blue-blooded frisky friends, and it’s why you should too.
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