Horseshoe Crab: Living Dinosaur

Jamaica Bay Wildlife Refuge, in Queens, is a quiet place where the sounds of the city fade away and there is only the sound of breeze rustling through the leaves of trees, the birds singing in the trees, and the smell of salt water in the air.

It is home to many species of plants and animals, including: Osprey, Bats, Swans, Ducks and Sandpipers. People can visit Jamaica Bay and enjoy nature by bird watching, hiking, taking a boat into the bay and participating in local events.

Swans at Jamaica Bay. (Photo by Rhia Singh)

On Sunday, May 22, 2016, naturalist, Mickey Cohen and Northeast Chapter President of the American Littoral Society, Don Riepe, led a Horseshoe Crab Walk. On the walk, participants observe horseshoe crabs mate and lay eggs. The goal of the walk was to make people aware of the ecological and medical benefits of these strange looking creatures.

Horseshoe crabs, named this because of the shape of their shell, have walked the Earth for about 300 million years, earning them the nickname, “living dinosaur”. According to the Florida Fish and Wildlife Conservation Commission, there are four species of Horseshoe crabs and only one, Limulus polyphemus, is found in North America along the Atlantic and Gulf Coasts. The other three species are located in Southeast Asia.

Horseshoe crabs have an exoskeleton made of chitin, compound eyes, five pairs of legs with pincers, book gills, and a tail. Exoskeletons made of chitin are strong due to the addition of calcium carbonate. They provide horseshoe crabs protection and support.

The two large compound eyes are located toward the center of the top of the shell and they have optical nerves that are easily identifiable. The light sensors in the compound eyes allow the horseshoe crab to see in shades of grey and find possible mates. Research of the compound eyes on horseshoe crabs has improved scientists understanding of the function of the human eye. Horseshoe crabs also have five other eyes located on the top of the shell, one eye on the tail, and a pair of eyes located near the mouth. The eyes allow the horseshoe crab to receive light and find food.

The legs with pincers, allow the horseshoe crab to walk on land, swim in water, and move food into its mouth. The pincers are used to grab food and attach to mates.

The book gills, named so because they seem like pages in a book, allow the horseshoe crab to conduct respiration in water.

The tail assists horseshoe crabs with movement. Horseshoe crabs tend to migrate independently and not in groups. However, the temperature of the water they live in signal when it is time for them to interact to find mates.

Horse Shoe Crab
Horseshoe Crabs mating at Jamaica Bay. (Photo by Rhia Singh)

Horseshoe crabs tend to mate during high tide, specifically during the full moon and new moon. They lay their eggs on land and it takes about two weeks for the horseshoe crabs to hatch. The eggs that do not hatch within two weeks, will lay dormant until there is another high tide. Horseshoe crabs are an r-selected species, meaning that they lay many eggs ensuring the survival of some of the offspring.

Predators, such as: sharks and sea turtles, threaten Horseshoe crab populations. Another main predator of horseshoe crabs are humans.

Cohen explained, “Researchers use the copper-based blood of horseshoe crabs to test the purity of human blood. Bleeding the animal is not harmful to the animal, if done correctly. If the copper-based blood comes in contact with a toxin, it begins to congeal around it and stops it from spreading.”

Endotoxin is the specific toxin that the copper-based blood binds to, according to Alexis Madrigal, author of the article, “The Blood Harvest”. Endotoxin is substance on a bacterial cell wall released when the bacterium ruptures or disintegrates. Copper blood allows scientists to test the purity of blood used in transfusions.

The Department of Environmental Conservation Division of Marine Resources passed regulations that limit the number of Horseshoe crabs that can be mined to prevent the horseshoe population from decreasing and becoming endangered.

Horseshoe crabs are also hunted because of their appearance. Some people think Horseshoe crabs are dangerous because of their appearance. However, their appearance and anatomy has allowed them to survive millions of years on Earth and hopefully they will be able to survive millions more.     

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