The horseshoe crab has carved its way into a unique niche of species. Despite what its name might lead on, it is neither a crab nor a crustacean by definition, instead belonging to the arthropod distinction along the likes of spiders and scorpions. These resilient creatures have earned their rare title of ‘living fossils’ as the existing horseshoe crabs of today morphologically resemble their fossilized ancestors, dating all the way back to the Paleozoic era,445 million years ago.
The exaggeration ‘not in a million years’ could be said to be the horseshoe crab’s motto. The horseshoe-shaped exoskeleton that shields the soft body of the crab has suited all of its needs. The shell functions as a perfect defence, but it also helps keep the crab mobile with its hydrodynamic design. The sheer success of survival has proven that ‘if it ain’t broke, don’t fix it’ as it has quite literally not undergone any major redesigns in millions of years. The second most distinct feature which may give the crab a bad reputation is its tail, also known as the telson. While it may be assumed sharp and dangerous due to its resemblance of a stingray’s tail, it is deceptive in function. Instead, it is used as a sensory organ, containing the largest abundance of light-sensitive receptors found on the crab. An even greater responsibility of the tail is flipping the crab over if it was unfortunate enough to be thrown belly-up with the tide. This is especially important as many shelled animals—turtles, crabs, and beetles, to name a few—know the embarrassment of being upturned without a means to get back on their feet. This description is not meant to discredit the horseshoe crab, but rather to highlight the harmlessness and sensitivity of these creatures.
This million-year existence is now in decline due to a unique property of their blue blood. Certain invertebrates share this same phenomenon, where instead of oxygenating their blood with hemoglobin like mammals would, their blood utilizes hemocyanin which is also responsible for the distinct blue colour observed. What sets the horseshoe crab apart however, are the amoebocytes found circulating within their blood. While these cells function to protect their body from foreign pathogens, much like the white blood cells found circulating in human blood, a factor they secrete is what is sought after. Amoebocytes produce limulus amoebocyte lysate, or LAL for short, which coagulates visibly and instantaneously upon contact with trace amounts of pathogens like bacterial endotoxins or fungi. This is incredibly useful for the crab, as LAL can combat infection, but it is also incredibly valuable in medical safety for testing sterility of medical equipment—in particular, reporting bacterial endotoxin contamination. Endotoxins area major concern in hospital settings as they are notoriously difficult to remove due to their high heat and pH stability. For that reason, the LAL that the horseshoe crabs possess has seen global demand in order to carry out diagnostic sterility tests. However, for that to happen, large amounts of crabs need to be harvested to obtain their blood to meet the markets’ demands.
The process of hunting and harvesting horseshoe crabs is grim. Reports have shown that over 400 000 crabs are harvested annually across the world. Captured on ocean shores, the handling of these creatures is not done with care. They are often transported in poor conditions to faraway facilities where their blood can be harvested in a 1-3-day process. Before being returned to their habitat, the mortality rates reach up to 30% from the stressful process and from greedy practices which over bleed the crabs. Unfortunately, in some cases, it is suspected that instead of returning the crabs to the ocean, they are sold as live bait or produce.
Scientific advancement has become a beacon of hope to save the increasingly threatened population of the horseshoe crab. In the late 1980’s, researchers at Japan’s University of Kyushu discovered that the molecule in LAL responsible for the important clotting reaction, called limulus clotting factor C (rFC), could be manufactured synthetically in a laboratory. This led Dr. Jeak Ling Ding from the National University of Singapore to create a patent for generating rFC, allowing for its distribution in 2003. Over time, as demand for rFC remained high across the world, more companies have developed their own patented blueprints to generating the synthetic alternate with comparable costs to the cruel process of horseshoe crab harvesting. This projected towards a future where seeking these crabs for their blood would come to an end. However, in July 2020, rCF was denied equal standing with LAL for testing medical sterility by the United States Pharmocopeia. This means that it will be more difficult for companies to prove synthetic rFC is comparable in its effectiveness and precision to the natural counterpart, possibly promoting a resurgence in the demand for horseshoe crab blood.
A sense of urgency must be recognized when a million-year-old species becomes threatened in a matter of generations because of the purpose they serve to an industry. There is optimism ahead as scientific research continues to trailblaze synthetic alternatives to naturally-occurring resources previously obtained through cruel practices. With that being said, the hunt for the horseshoe crab is on its last legs before new practices driven by scientific advancement can take over.
References
1)https://dnr.maryland.gov/ccs/Pages/horseshoecrab-evolution.aspx#:~:text=Fossils%20of%20horseshoe%20crabs%20have,relative%20of%20the%20horseshoe%20crab.
2)https://myfwc.com/research/saltwater/crustaceans/horseshoe-crabs/facts/
3)https://www.frontiersin.org/articles/10.3389/fmars.2018.00185/full
Philip Barbulescu
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