Horseshoe crabs are very interesting creatures that are predominantly present on sandy beaches. They are famous for not having any predators except for humans who use them as bait for fishing. Horseshoe crabs belong to the genus Limulus and are of the species Polyphemus. They are usually found in muddy or shallow waters and would come on shore for mating/breeding. The body of the horseshoe crab is made of a hard shell called a carapace. The horseshoe crab has book gills for respiration that help it breathe underwater as well, and they also help them to swim. They also have ten legs present under their shell, spines present on the abdomen and also have a long tail. (Bio Web).
As far as the ecological importance of horseshoe crabs is concerned, they are mostly important for the marine food chain. Their consumption of food consists of small crustaceans such as barnacles, shrimps, crayfish, water fleas, etc. as well as invertebrates like mollusks, worms, and other small fish. They are also commonly called secondary consumers. (Chung). Conversely, horseshoe crabs are an important prey for quite a number of organisms. There are many varying species of shore birds that eat horseshoe crabs mainly when they are migrating from a region. (New World Encyclopedia). They prey on horseshoe crabs because they serve them as a main source of fat. Apart from the birds, there are many species of fish, sharks and also sea turtles that consume horseshoe crabs. The eggs and larvae of the horseshoe crab are prey to the above mentioned marine life. (National Wildlife Federation). As the horseshoe crabs age, they grow slower, and their shedding process is lessened significantly.
When this happens, it can be easily spotted when they establish a relationship with other organisms. The horseshoe crab has multiple relations with many small organisms thus forming a symbiotic relation with them. Commensalism is the main feature of this relationship as the benefit is formed without causing harm to the other. (New World Encyclopedia). Upon their bodies, there survive many sponges, snails, and bivalves that use horseshoe crabs for many purposes. For instance mud, snails and periwinkles lay their eggs on their backs. Yet, some small organisms can be parasitic as well. For instance limulus leeches will lay their eggs around the book gills and joints of the female crab causing the release of a toxic chemical. (Chung).
The reproductive process of horseshoe crabs begins in the months of May and June. They migrate to shallow waters during the mating season. The lifecycle of the horseshoe crab is completed in several stages. The eggs are laid in the low water line due to more warmth. They dig nests in the sand and lay the fertilized eggs. This is known as spawning. As the daylight hours increase, the crabs move from the waters onto the shore. The peak of this activity is during a full moon and high tide. The eggs laid in a cluster range from three to four thousand in number. A female horseshoe crab can lay up to 80,000 eggs in a year. (Bio Web). The eggs hatch in 14-30 days after being fertilized. When the eggs hatch, the larval stage begins. For about a period of 6 days, the larvae swim about and feed themselves. When they settle in the shallow waters, the process of molting begins. Within 20 days, the first juvenile will appear after the molting. The juvenile horseshoe crabs spend the first two summers in the intertidal flats. Molting keeps recurring for 2 to 3 years of their life. The horseshoe crab grows into a sexually mature adult crab in a period of about 9 to 11 years. Morality is not determined by factors other than natural ones like disease and parasites, use as bait and fishing, and getting stranded on the beach. (Chung).
Work Cited
Bio Web. Atlantic horseshoe crab. 2015. Web. 20 Jan 2016.
Chung, Matthew. Limulus polyphemus – Atlantic horseshoe crab. TolWeb. 2015. Web. 20 Jan,
2016.
National Wildlife Federation. Horseshoe crab. 2015. Web. 20 Jan 2016.
New World Encyclopedia. Horseshoe Crab. 2015. Web. 20 Jan 2016.
