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What has 10 eyes, blue blood, and outlasted the T-Rex?

Sep 05 2017

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K-12

These quirky creatures have roamed the Earth for over 450 million years. Having survived five mass extinctions, horseshoe crabs (Limulus polyphemus) are evolutionary wonders. Despite their incredible resilience, their  numbers are dipping dangerously low. In the last 15 years their population has dropped by about 90% in the Delaware Bay alone. Not only are these species ecologically and historically valuable, their blood is indispensable to modern medicine. Horseshoe crabs provide a multifaceted topic to be used in classes from science to social studies. Use this current events piece to spark a debate on the conservation and ethics and discuss possible solutions to this problem. Keep reading for more information on horseshoe crabs and the ecological and human health predicament that is quickly approaching.

The name horseshoe crab is deceiving – they are actually arthropods, not crustaceans as their name implies. Sporting ten eyes and seven pairs of legs, these creatures are related more closely to spiders than crabs. While their armored body and spike-like tail may seem intimidating, horseshoe crabs are harmless. Their tail is used to right themselves when flipped by rough waves or curious humans and their tough shell helps them withstand extreme temperatures and salinity. Most astonishingly, they can survive up to a year without food. It is no wonder this species has lived longer than over 99% of the species in our planet’s existence. However, human exploitation may be the one event no adaptation can survive. Horseshoe crabs are unfortunately a great example of the tragedy of the commons.

There is still much to be discovered about the importance of these living fossils, but with their 450 million year existence, it is safe to say they have laid the foundation of the oceanic and coastal ecosystems. One of their most important ecological contributions is as a food source for many species, including endangered shorebirds and turtles. Each spring, horseshoe crabs meet on the beach to mate and lay clusters of thousands of eggs in the sand with the hopes that predators do not find them. Regardless, the eggs are a fundamental food source for many species, particularly the loggerhead sea turtle and migrating shorebirds. With this food source declining, many species have begun shifting their diet to new food sources. The loss of horseshoe crabs and their eggs has a cascading effect on the ecosystem with many of the impacts still unknown.

Horseshoe crab blood is extracted at a lab. Their blood is copper-based and blue when exposed to oxygen.

Human Impact & Human Health

Horseshoe crabs are an essential part of our world ecologically and now medically. Almost 50 years ago, scientists discovered we could extract the compound limus amebocyte lysate (LAL) from their blood and use it to test for contamination in virtually all vaccines, surgical tools, and medical devices – saving countless lives by preventing infection.  Valued at about $15,000 a quart, this unique substance has become critical to our medical system. But this life-saving quality now threatens the survival of the species.

To obtain a supply of the anti-microbial compound, horseshoe crabs are removed from the ocean and transported to a bleeding facility. Once there, about 30% of the blood from each horseshoe crab is extracted. The surviving individuals are trucked back to the ocean, to a different location than where they were plucked from to reduce the chance that they get harvested again. The mortality rate after blood extraction is about up to 29% – an improvement from near 90% when this phenomenon was first discovered. Perhaps it’s the puncture from blood extraction, rough transportation, or unknowingly bleeding a crab more than once, the exact cause of death is unknown.  However, one company alone bleeds about 200,000 horseshoe crabs per year, and at 29% mortality, this unregulated loss of horseshoe crabs will cause an ecosystem collapse.

A Biomimicry Challenge: Save Human Life & A Species

Thanks to it’s bacteria-detecting blood, the survival of horseshoe crabs is intimately linked to human health. How can we protect the species and keep human patients safe from infection? This presents a challenge to innovate using the principles of biomimicry. Scientists, engineers, and artists have used biomimicry to replicate natural functions to mediate many human challenges. From Velcro to solar panels, there are plenty of successful innovations using nature as inspiration. It is time to concentrate efforts in developing an artificial substance that serves the same purpose as horseshoe crab blood for the health and sustainability of both people and the ecosystems that support us.


Resources:

This creature has 10 eyes, legs that chew and blood that saved your life – Washington Post, 07/04/17

A bird, a crab, and a shared fight to survive – The New York Times 06/05/12

The Blood of the Crab – Popular Mechanics 04/13/17

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