Horseshoe Crabs: A Prehistoric Facination

Recently, Kim has asked me to become an expert on a truly fascinating creature, the horseshoe crab. After about a hour and a half of research, I became enamored by this illustrious, prehistoric creature. Needless to say, I had to share some horseshoe crab facts and fictions.

 Me with a horseshoe crab found on Andy's Way.

Me with a horseshoe crab found on Andy's Way.

1.) There are only 4 species of horseshoe crabs that inhabit the globe today, only one of which is found in North America. This species, Limulus polyphemus, can be found throughout the entire Atlantic Coast.

2.) Horseshoe crabs are not crabs at all. They are more closely related to the arachnids than the crustaceans (think spiders or scorpions rather than lobsters or shrimp).

3.) Ancestors of the horseshoe crab date back almost 450 million years. Just to put that into perspective, that is 200 million years before the first dinosaur came into existence.  Remarkably, the horseshoe crab's unique morphology has changed very little throughout that time.

4.) Almost always thought of as being dangerous due to their spine-like tail, horseshoe crabs are harmless. Their tail is predominately used to orient themselves upright if they are accidentally overturned.

  Limulus polyphemus  on the coast of New Jersey

Limulus polyphemus on the coast of New Jersey

5.) Horseshoe crabs have an interesting mating ritual. They nest in massive aggregations in the spring and summer, usually on mid-Atlantic beaches. Male horseshoe crabs orient themselves parallel to the coastline and cut off the females as they approach the shore. Once the male locates a female, he attaches himself to her using his specialized front claws. From there, they both ascend to the beach. The males fertilize the eggs as the female lays them on the sand in what many call a nest. This nesting activity usually takes place during higher tides, within three days of a full moon. The horseshoe crab larvae surface from the nest several weeks after the eggs are laid.

  Limulus polyphemus  mating off the coast of Delaware in 2012.

Limulus polyphemus mating off the coast of Delaware in 2012.

6.) Mature horseshoe crabs spend the majority of their time on sandy bottoms of intertidal flats and feed on a variety of invertebrates. They use their legs to pulverize their food before ingestion due to their lack of mandibles and teeth. They also have gizzards to assist in the pre-stomach digestion process.

7.) Horseshoe crabs are a vital part of the coastal food web. It is estimated that horseshoe crab larvae account for over 50% of the diet of many shorebirds; not to mention the fact that fish also prey on the horseshoe crab larvae.

8.) For the last couple decades, the blood of the horseshoe crab has been vital to the biomedical industry. The blood is copper-based and a metallic blue in color due to a unique amino acid known as Limulus amebocyte lysate (LAL).

  Limulus polyphemus  getting bled. Researchers maintain that it is virtually harmless to the animal. Horseshoe crabs can give blood up to four times a year.

Limulus polyphemus getting bled. Researchers maintain that it is virtually harmless to the animal. Horseshoe crabs can give blood up to four times a year.

This amino acid has properties which coagulate blood in the presence of small amounts of bacterial toxins. This allows researchers to introduce the amino acid onto medical equipment and into intravenous drugs to test their sterility.

9.) Horseshoe crabs have very primitive compound eyes with monochromatic vision. The eye of the horseshoe crab is compartmentalized, allowing researchers to stimulate and repress nerve endings leading to huge advances in optic and neurological research.

10.) Although these "living fossils" have been around for a very long time, resent research has determined that the horseshoe crab is declining in numbers. Scientists are unsure of the exact factors leading to this decline; however, they attribute most of it to a degradation of habitat. (Unfortunately, man plays a huge role in this downfall.) In an attempt to stabilize the horseshoe population, The Atlantic States Marine Fisheries Commission developed a Horseshoe Crab Fishery Management Plan. Within the plan, it requires "all Atlantic Coastal states to identify horseshoe crab nesting beaches. (FFECC, 2014)" They have also initiated the "Turn Me Over Campaign", with a main objective of encouraging the public to assist flipped over horseshoe crabs by holding them on either side of their shell and orienting them upright. 

**All of the information and pictures used within this post were gathered from the Florida Fish and Wildlife Conservation Commission. For more information about the horseshoe crab or what you can do to help the cause, please visit their website at www.myfwc.com.