The Atlantic horseshoe crab, limulus polyphemus, have existed for approximately 450 million years, hence its nickname of “the living fossil.” This species has survived ice ages, the separation of Pangea, and several mass extinctions, including the Cretaceous-Tertiary Extinction that wiped out the dinosaurs, and the Great Dying, which killed 90% of life on Earth 250 million years ago. However, the downfall of this species may ultimately be caused by humanity.
Over the past couple of decades, the horseshoe crab has encountered its most serious threat from exploitation in clinical research. Horseshoe crabs have been used in laboratories, mainly due to the significant pharmaceutical value of their blood. Additionally, the horseshoe crab has been utilized in vision research conducted by the American physiologist Keffer Hartline that resulted in his winning of the Nobel Prize in Physiology and Medicine in 1967. The demand for these sea creatures is so high that horseshoe crab blood can cost anywhere between $35,000-$60,000 per gallon.
In the 1950s, an American researcher named Frederick Bang discovered specialized amebocytes in horseshoe crab blood that became viscous as a means of obstructing bacterial invasion. Amebocytes are mobile amoeba-like cells within the blood of horseshoe crabs and other invertebrates that contain various proteins necessary for the organism’s survival. The discovery of these amebocytes has led to the widespread drawing of the arthropod’s blue blood to obtain specific proteins now known as limulus amebocyte lysate, or LAL.
Because LAL thickens when it comes into contact with endotoxins, which are toxins often found in bacterial cells that cause diseases such as botulism and various forms of neurodegeneration, horseshoe crabs have became heavily harvested with the intent of using their blood to test the safety of medical products. LAL has extraordinary capacities in testing implants, vaccines, and medical instruments for potentially dangerous impurities.
Due to their incredible potential in clinical research, the horseshoe crab is poached at alarming rates by numerous research laboratories and institutions. The standard protocol is to draw their blood and release them once they’ve fulfilled their purpose in the lab. However, an estimated 50,000 horseshoe crabs die in the process every year due to mishandling. Labs often draw too much blood from the animal or make a mistake in the process that leads to infection.
A study conducted by the University of New Hampshire and Plymouth State University revealed that over 400,000 horseshoe crabs are bled for clinical research yearly, with a mortality rate of approximately 20%. The research study also presented evidence that when released, the surviving crabs become weak and disoriented, and that female horseshoe crabs may have reduced ability to produce offspring. An inflated mortality rate along with a decrease in reproduction due to human activity has resulted in the species’s conservation status falling to “vulnerable” in 2016.
Overharvesting for clinical research, while the most prominent threat to the species, is just one aspect of human activity contributing to the horsecrab’s dwindling conservation status. In addition to pharmaceuticals, the horseshoe crab is threatened by the fishing industry due the animal’s ability to act as bait for eels and conch. A loss of habitat provides another significant factor in the vulnerable status of the species, largely due to sea walls that block their access to the shore while acting as an agent against beach erosion.
The gradual demise of the horseshoe crab is especially alarming at an ecological level due to their important role in aquatic ecosystems. Their eggs serve as a crucial aspect of the food chain as the main source of food for various shorebirds such as seagulls and ospreys. Adult horseshoe crabs additionally serve as prey for larger animals such as sea turtles, alligators, and sharks. Without the provision of their main food source, the conservation status of the animals that depend on the horseshoe crab may also be at stake.
As horseshoe crabs also function as bottom feeders by eating smaller organisms like bacteria, they help maintain the balance of marine water composition. Additionally, their presence in the ecosystem is important for maintaining the strength of biogeochemical cycles including the water cycle and the carbon cycle. Such cycles are crucial for photosynthesis and the survival of various species of plants, animals, and insects within the horseshoe crab’s ecosystem.
Numerous conservation efforts have been made to re-establish the horseshoe crab population around the world. The Wetlands Institute in Stone Harbor, New Jersey brought a coalition of scientists and volunteers to conduct yearly censuses of the Atlantic horseshoe crab population since 1991. The organization has recognized a 90% decrease in the horseshoe crab population in the Delaware Bay over the last 15 years and has been pivotal in getting the species added to the New Jersey Endangered Species List. The Wetlands Institute is also a major partner in the reTURN The Favor program that focuses on rescuing overturned horseshoe crabs on the beach while encouraging the public to do the same through various sign postings along public beaches.
Other initiatives to save the horseshoe crab include research developments in synthetic LAL alternatives. Researchers at the University of Singapore found that a synthesized element called recombinant Factor C (rFC) could pave the way for a future of endotoxin detection technology free from animal cruelty. Despite concern regarding the efficacy of rFC, this pioneering research has inspired similar studies to obtain an alternative method of testing medical equipment without endangering the horseshoe crab.
The horseshoe crab species has endured much while enhancing the safety of medical equipment and procedures for humans. Without LAL, it would be impossible to recognize harmful bacteria residing on medical equipment. This could turn every vaccine, surgery, or any other procedure into a potential health hazard. It is in humanity’s best interest to focus on the conservation of the Atlantic horseshoe crab, for their safety as well as our own.
Sources
Anderson, R. L., Watson, W. H., III, & Chabot, C. C. (2013, December 01). Sublethal Behavioral and Physiological Effects of the Biomedical Bleeding Process on the American Horseshoe Crab, Limulus polyphemus. Retrieved November 20, 2020, from https://www.journals.uchicago.edu/doi/abs/10.1086/BBLv225n3p137?journalCode=bbl
Ballard, B. (2019, June 7). Horseshoe crabs are being exploited for their life-saving blood. Retrieved November 20, 2020, from https://www.theneweconomy.com/technology/horseshoe-crabs-are-being-exploited-for-their-life-saving-blood
Florida Fish and Wildlife Conservation Commission. (2020). Facts About Horseshoe Crabs and FAQ. Retrieved November 20, 2020, from https://myfwc.com/research/saltwater/crustaceans/horseshoe-crabs/facts/
The Horseshoe Crab. (2009). Ecological Importance of Horseshoe Crabs. Retrieved November 20, 2020, from https://horseshoecrab.org/con/con.html
Maloney, T., Phelan, R., & Simmons, N. (2018, October 12). Saving the horseshoe crab: A synthetic alternative to horseshoe crab blood for endotoxin detection. Retrieved November 24, 2020, from https://journals.plos.org/plosbiology/article?id=10.1371%2Fjournal.pbio.2006607
Maryland Department of Natural Resources. (2020). Horseshoe Crab Blood. Retrieved November 20, 2020, from https://dnr.maryland.gov/ccs/Pages/horseshoecrab-medical.aspx
NASA: Share the Science. (2002, January 28). The Great Dying. Retrieved November 20, 2020, from https://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction
The Nobel Prize. (2020). The Nobel Prize in Physiology or Medicine 1967. Retrieved November 20, 2020, from https://www.nobelprize.org/prizes/medicine/1967/hartline/biographical/
Sacred Heart University. (2020). Horseshoe Crab History. Retrieved November 20, 2020, from https://www.sacredheart.edu/academics/colleges–schools/college-of-arts–sciences/departments/biology/project-limulus/horseshoe-crab-history/
University of Gothenburg. (2010, October 04). Climate change affects horseshoe crab numbers. Retrieved November 20, 2020, from https://phys.org/news/2010-10-climate-affects-horseshoe-crab.html
Watts, J. (2018, November 03). This crab could save your life – if humans don’t wipe it out first. Retrieved November 20, 2020, from https://www.theguardian.com/environment/2018/nov/03/horseshoe-crab-population-at-risk-blood-big-pharma
Wetlands Institute. (2020). Horseshoe Crab Conservation. Retrieved November 20, 2020, from https://wetlandsinstitute.org/conservation/horseshoe-crab-conservation/
Zhang, S. (2018, May 09). The Last Days of the Blue-Blood Harvest. Retrieved November 20, 2020, from https://www.theatlantic.com/science/archive/2018/05/blood-in-the-water/559229/