Horseshoe crabs are living fossils in our coastal bays

Have you ever seen a living fossil?

Horseshoe crabs spawn in Maryland’s coastal bays from May through July each year. These funny looking creatures go back 445 million years. Some people call them “living fossils” because of their ancient roots.

Although they are referred to as crabs, they are not crabs at all. Horseshoe crabs are actually more closely related to spiders.

A single female horseshoe crab can lay 90,000 eggs; only about 10 of these babies will survive to maturity. What happens to the rest of them?

Horseshoe crab eggs are a significant and valuable food source for shorebirds, turtles and fish. Female crabs visit our bay beaches during full and new moons to lay their eggs; this is referred to as spawning.

Did you know a female crab is, on average, 25 percent larger than a male horseshoe crab?

Another way to differentiate between the sexes is to look at the claws underneath. A male horseshoe crab has clasping claws that help him hang onto the female while fertilizing her eggs; the female lacks these boxing glove-shaped appendages.

Horseshoe crabs mainly eat clams and mussels, but may also sustain themselves with aquatic worms, algae and carrion.

These prehistoric creatures have nine eyes, and are made up of three distinct sections:

•The head, which contains all of their major organs

•The abdomen, which contains the gills and muscles to move them about

•The tail, which is called a telson

Horseshoe crabs are ecologically important — and also harmless to humans. Their telson may look sharp, but it doesn’t sting like a stingray; it is mainly used for maneuvering and helps to turn the crab upright when he or she gets flipped over.

Many horseshoe crabs get hung up and perish on rip rap barriers installed to protect properties from wave action and erosion. This is a great reason to look into installing a living shoreline to prevent shoreline erosion, which supports wildlife at the bottom levels of the food chain and therefore our entire coastal bays ecosystem.

If you see a horseshoe crab stuck in the rocks, feel free to pick it up by grabbing each side of the shell and put it back into the water; this will help the little guy out tremendously.

Never pick up a horseshoe crab by its tail; this will result in injury to the animal. If you’d like to become a Horseshoe Crab Steward and assist the Maryland Coastal Bays Program in rescuing horseshoe crabs stuck in riprap barriers, email Amanda at amandap@mdcoastalbays.org.

In addition to being an important food source to many species throughout the coastal bays food web, horseshoe crabs provide humans with a valuable resource in regards to public health — limulus amebocyte lysate, or LAL. This substance is extracted from the horseshoe crab’s blue-colored blood, which is blue due to the blood being copper-based instead of iron-based like human blood.

We use LAL in the biomedical industry to test for the presence of bacterial toxins. The discovery of this lifesaving substance occurred in 1971. Since then, all vaccines, injectable drugs, intravenous solutions and implantable medical devices that are certified by the Food and Drug Administration are required to be tested using LAL.

Horseshoe crabs are also harvested for use as bait for American eels and whelks.

Many species are dependent on horseshoe crabs for survival, but populations on the East Coast of the United States have decreased. Abundance of horseshoe crabs has not been well defined, but many areas have seen declines.

The Maryland Coastal Bays Program assists the Maryland Department of Natural Resources by conducting an annual Horseshoe Crab Survey to measure spawning abundance in this area.

The survey has been in existence since 2002 and provides valuable data used in fisheries management. Surveys start in late May and continue through early July, with sampling taking place once every two weeks.

Amanda Poskaitis is the watershed program coordinator for the Maryland Coastal Bays Program.