A History of Horseshoe Crabs, Ecology and Human Health by William Sargent – Review

An updated look at an ancient wild animal that helps us test the safety of countless vaccines but now, thanks to our unsustainable overuse, it’s endangered

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The Atlantic horseshoe crab, Limulus polyphemus, is an ancient creature that has inhabited the Earth virtually unchanged for over 450 million years. The species predates humans and even dinosaurs. It lives along the east coast of North America, and hundreds of thousands of people leave the sea to spawn on the sandy beaches of New England to the mid-Atlantic, the greatest number of ‘between them climbing ashore in Delaware Bay.

“You can imagine a horseshoe crab living halfway between the marine world of a trilobite and the terrestrial world of a bug,” writes author, marine biologist and science writer William Sargent. (p. 21.) “Horseshoe crabs only come to earth once a year to lay their eggs. If they are disturbed during spawning, they curl up much like bedbugs for protection. As long as they keep their gills moist, they can survive for several days in this curled up defensive posture. The blood of both animals is copper, not iron. Some scientists believe their common ancestor developed this copper-based blue blood when copper was more available in the oceans than iron.

It’s their blue blood that makes Limulus vitally important: their blood contains critical immune cells which are extremely sensitive to toxic gram-negative bacteria. These bacteria are enclosed in a thick, sugar-like outer layer made up of endotoxins, which are poisons that cause burning fevers associated with life-threatening illnesses like typhoid, spinal meningitis, gonorrhea, and toxic shock syndrome. When gram-negative bacteria invade a horseshoe crab, their primitive immune cells, called amebocytes, clot around the bacteria, inactivating them and protecting the horseshoe crab from deadly toxins.

Several smart scientists and observers have noticed this peculiar trait and have devised a way to adapt horseshoe crab amoebocytes to test vaccines and other drugs against bacterial contamination. This essay, the Limulus The amebocyte lysate (ALL) endotoxin test was a major breakthrough that has been used around the world since the 1970s to protect people from a variety of dangerous diseases. More recently, it has also been used to detect bacterial contaminations on laboratory equipment, on Mars Rover, and even in humans. Of course, horseshoe crabs probably have a very different view of the situation: They are captured and bled for their incredibly valuable and medically useful cobalt blue blood.

In this fascinating book, Crab Wars: A History of Horseshoe Crabs, Ecology and Human Health (Brandeis University Press; 2021: Amazon United States / amazon United Kingdom), we learn the story of Limulus and their key place in the ecology of the east coast of one of their most eloquent longtime fans. Dr Sargent alternates between his own memories, many of which date back to his childhood, and remarkable scientific discoveries about Limulus, and the multi-million dollar industry that has grown around it. The book details the discovery and development of the LAL endotoxin test, the careless overexploitation of these iconic animals as fish bait by fishermen, as a blood donor by pharmaceutical companies – and even by some scientists – and the many environmental, political and legal entanglements that this inspired on the ultimate fate of these animals.

A proven lifeline, the LAL endotoxin test is the foundation of a multi-million dollar pharmaceutical industry. For example, every vaccine and drug certified by the FDA must be tested using LAL, and LAL comes from only one species of wild animal. It is therefore deeply disturbing that Limulus populations are declining along the east coast. As the author notes, this sounds like the recipe for disaster:

“… if we were to lose all the lobsters, striped bass or shrimp on the east coast, it would be an environmental tragedy.” But if the East Coast lost all of its horseshoe crabs, it would be a major medical disaster. While we protect our precious food species with strict regulations, to date we have only begun to protect our much more valuable populations of horseshoe crabs. So, it is time for all states on the east coast to follow South Carolina’s lead and only allow horseshoe crabs to be used for biomedical purposes. “ (P. 129, Crab wars, second edition, by William Sargent, 2021.)

In addition to worldwide use by the medical industry, Limulus are an irreplaceable foundation upon which the East Coast ecosystem rests. Hundreds of thousands of shorebirds depend on food Limulus eggs to be fattened before undertaking the last segment of their northward migration. Birds that do not eat enough Limulus eggs before they reach their breeding grounds are too thin and weak to lay their own eggs. Many die.

Moreover, even as Limulus attract shorebirds, shorebirds attract thousands of bird watchers and eco-tourists from all over the world to watch and photograph the spectacle. And wherever people go in vast hordes, their money also travels with them, infusing local economies with much-needed cash.

Consequently, the conservation of Limulus is an extremely relevant question for many key reasons, and these competing interests are driving researchers’ continued efforts to develop recombinant lysates to complement or replace LAL as diagnostic test products in the future.

This beautifully written book is not fiction, but it reads like a particularly gripping novel that I just couldn’t let go. It’s filled with natural history, scientific discoveries, pharmaceutical developments, and plenty of politics, and yet Dr. Sargent tells the story of horseshoe crabs with tremendous compassion and poise. But we can’t forget that Limulus populations continue to decline, which has profound implications not only for the future of the animals themselves, but also for the ecosystems that depend on them.

Recently updated from the original book published in 2002, this second edition includes five additional chapters and a new epilogue that contains surprising information regarding COVID-19 vaccines. Although published by an academic press, this book is pleasantly accessible for the non-specialist.

Ultimately, the fascinating story of the Horseshoe Crab is thought-provoking and thought-provoking reflection on the unintended consequences of scientific progress and the dangers posed when self-regulating industries control a finite natural resource.

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