Image courtesy of National Wildlife Federation
The Atlantic horseshoe crab, Limulus polyphemus, is a primitive arthropod species that has been on the earth for nearly 450 million years. Sometimes referred to as living fossils, they resemble prehistoric creatures that have somehow eluded morphological evolution. They are more closely related to spiders and scorpions than true crabs and they survive on small crustaceans, worms, and sometimes algae. The Atlantic species ranges from Maine down along the American Atlantic coast, into the Gulf of Mexico, and parts of Northern Mexico, but U.S. legislation only protects those along U.S. coastlines. Besides Limulus polyphemus, there are three other extant horseshoe crab species that reside in the Indo-Pacific region of the earth. Despite being expert survivors, today their populations around the world are faced with threats such as habitat loss and overharvesting.
Horseshoe crabs are not normally captured to be eaten in the U.S., but rather they are harvested for their blue blood, which gets its color from a protein called hemocyanin that contains copper rather than iron. Their blood also contains lysate, which helps detect bacterial toxins by clotting. The biomedical industry uses this feature to test equipment, vaccines, and water for possible contamination. Until a proper substitute is found, we still depend on this extremely valuable feature for our health. There have been efforts to farm horseshoe crabs in aquaculture, but this is still a developing process. This means that until then, wild horseshoe crabs are still at risk for overexploitation.
Most harvesting practices release horseshoe crabs back into the coast, but 5% to 20% die during the extraction process. Eastern states such as South Carolina, Delaware, New Jersey and Maryland have specific state laws implemented to protect the Atlantic horseshoe crab, requiring permits and outlining taking and handling procedures for approved research purposes and facilities. The Atlantic States Marine Fisheries Commission currently manages their harvest, specifically targeting areas like the Delaware Bay, which sees the world’s largest concentration of horseshoe crabs during spawning season. For 2023, the harvest limit for male horseshoe crabs in the Delaware Bay is 475,000 while the limit for female horseshoe crabs is zero. These limits are expected to increase horseshoe crabs populations and lift their IUCN status from “Vulnerable” to hopefully “Least Concern”.
Besides harvesting, horseshoe crabs face other threats such as loss of coastal habitat and pollution. Locals who have access to the Atlantic coast can take action to keep beaches clean for successful spawning. Reducing runoff pollution is another way that we can protect horseshoe crab numbers, since harmful chemicals can change the water quality and threaten egg development. There’s limited knowledge regarding horseshoe crab numbers due to difficulty counting them, so scientists and volunteers work together during the spawning season from March to July to take a census of horseshoe crabs around the Delaware Bay area. Volunteers go through training that helps them identify and properly conduct surveys. More information about volunteering can be found here. The Atlantic Horseshoe crab is a vital part of the ecosystems it inhabits, and has contributed immensely to human medical advancements. Before this ancient species faces further threats, it’s up to us to learn more about them, continue to watch harvesting practices, and preserve coastal areas as they have known them for over the past 450 million years.
Sources:
Atlantic horseshoe crab, facts and photos. Animals. (n.d.). Retrieved February 28, 2023, from https://www.nationalgeographic.com/animals/invertebrates/facts/atlantic-horseshoe-crab
Atlantic States Marine Fisheries Commission. species - Atlantic States Marine Fisheries Commission. (n.d.). Retrieved February 28, 2023, from http://www.asmfc.org/species/horseshoe-crab
Delaware Bay Horseshoe Crab Spawning Survey. DNREC Alpha. (2022, February 21). Retrieved February 28, 2023, from https://dnrec.alpha.delaware.gov/coastal-programs/education-outreach/horseshoe-crab-survey/
Horseshoe Crab Limulus polyphemus. (2023). National Wildlife Federation. Retrieved 2023, from https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Horseshoe-Crab
Madrigal, A. C. (2021, June 14). The Blood Harvest. The Atlantic. Retrieved February 28, 2023, from https://www.theatlantic.com/technology/archive/2014/02/the-blood-harvest/284078/
Watts, J. (2018, November 3). This crab could save your life - if humans don't wipe it out first. The Guardian. Retrieved February 28, 2023, from https://www.theguardian.com/environment/2018/nov/03/horseshoe-crab-population-at-risk-blood-big-pharma