Bill Sargent has been fascinated with horseshoe crabs since childhood. As a boy he regularly explored the marshes, bays and tide pools of Cape Cod, Massachusetts, where he grew up. It was in this idyllic setting that he honed a keen interest in this unassuming and prehistoric creature.

This interest has woven itself into the fabric of Sargent’s life, leading him to study these living fossils for decades, publish research that has influenced a federal court case and write a book about the link between the horseshoe crab and human health. 

In a recent conversation with Kinute, Sargent outlined pharmacology’s interest in the horseshoe crab and how the survival of this 450-million-year-old organism has become essential to the multi-million-dollar, modern pharmaceutical industry. With global demand at an all time high, limited oversight in harvesting practices and self-reported mortality rates by the companies profiting from these creatures, this survival may be at risk. 

If the thought of the human race being dependent on harvesting the bright blue blood of an aquatic creature that has outlasted the dinosaurs sounds like the premise of a sci-fi novel, allow Bill Sargent to explain how this truth is stranger than fiction.  

Horseshoe crabs in the shallows. Courtesy of Bill Sargent

Tell us about your introduction to horseshoe crabs and how you ended up studying them.

I grew up in the summers on Cape Cod and I've just been intrigued with horseshoe crabs all my life. I've always been intrigued with them because they're so primitive and so innocent and gentle. After college I set up a little marine biology laboratory on the bay that I grew up in, and we had kids coming in from all over the country and we were collecting basic information on the bay and then we noticed that some scientists from the Marine Biological Laboratory in Woods Hole were collecting the crabs and we realized that they were collecting them for research purposes but there was also a scientist who was actually bleeding the horseshoe crabs in his garage. He wanted to start a company based on the blood of horseshoe crabs and he asked me if I'd like to become a partner. He needed to raise about $5,000 for it. I had no idea how you could raise $5,000, and I thought it was a flaky idea, so I turned him down. He sold that company about 20 years ago for $32 million. So don't come to me for any financial advice.

It was a really intriguing story, and I particularly was concerned with how the crabs were being treated because theoretically you should be able to go out, catch the crabs, bring them back to the laboratory, bleed them and then return them back to the waters with no mortality. But we were monitoring them, and we found sometimes you'd get up to 50% mortality. We collected a lot of data throughout the years.

Then, in the year 2000 there was a federal court case. The guys who were collecting the crabs had been collecting in the waters of the Cape Cod National Seashore for about 20 years, and nobody realized that they were doing it and that it was also illegal. It's illegal to make a profit off any animal that you catch from a National Park or National Seashore. 

So, George Buckley, who teaches at Harvard, had been studying the bay with me for years and we looked at each other and we decided, we’ve got all this data, this is the time to publish it. So we did, and I think really that was the critical piece that led to the banning of [harvesting] horseshoe crabs in the Cape Cod national seashore.

A juvenile horseshoe crab makes his way up the beach. Photo by The Tampa Bay Estuary Program | Unsplash

What interest does the biomedical community have in horseshoe crabs?

Anything that's going to come in contact with a human blood system, whether it's a syringe or a vaccine or a pacemaker, has to be checked that it's free of gram-negative bacteria, often called pyrogens in a hospital situation. Formerly, the way they would test things like vaccines, is all the pharmaceutical companies would have large colonies of live rabbits, and they would have a vat of vaccine and they would test it on the rabbits. They would inject the rabbit and if the rabbit kicked over and died, they knew that it was contaminated with gram-negative bacteria.

Then in 1976, I believe, was the swine flu scare, and President Ford decided that he would vaccinate every man, woman and child in the United States against swine flu. People started to have very serious neurological problems and they realized it was because the vaccines were contaminated with gram-negative bacteria. That was when they started using the horseshoe crab test, and they realized it was much more sensitive and easier to use and cheaper than the rabbit test. Millions and millions of peoples’ lives have been protected by horseshoe crab blood. 

Can you briefly describe how horseshoe crab blood is used to detect pyrogens? 

Pharmaceutical companies make vaccines in large batches of several hundred doses. The horseshoe crab blood is spun out to separate out the amoebocyte cells which are freeze dried into a fine powder. This powder is mixed in with the batch of vaccine. If it coagulates and forms a bright blue blob it means the batch is contaminated with pyrogens, which are the outer membrane of gram-negative bacteria and can lead to sepsis in humans.

What is the bleeding process like?

Basically, you catch the crab and you put it in a wooden rack upside down, and then you take the same size needle that a vet will use on a horse, and you put it in the hinge between the two parts of the of the horseshoe crab’s carapace, and then you get a free flow of blood. It's this bright cobalt blue blood and as soon as flow stops then you're supposed to stop the bleeding and you'll have taken about 30% of the blood out.

A horseshoe crab being bled. Courtesy of Save the Horseshoe Crab

How is it determined that a 30% drain rate was sustainable? 

It was basically how much they would give. In the early days they would exsanguinate the crabs. They would simply take all the blood out and then of course you'd get very close to 100% mortality.

How is the survival rate monitored now?

The companies are supposed to report the figures.

What properties of the horseshoe crab blood cause it to be blue?

It's a copper-based blood. It's similar to insects and some very ancient animals. It's because they're so old, as a species they're about 450 million years old, they evolved before there was oxygen on the planet, and so they used copper, which is not as efficient as iron at holding oxygen.

Horseshoe crabs nestle on a beach in Cape Cod. Courtesy of Bill Sargent

Has there been much of an outcry from animal rights groups in response to this practice?

Most of the pressure is coming from birders because they're concerned about the red knots, and they have a large constituency. There had been a ban on taking female horseshoe crabs because they were concerned that [red knots] weren't getting enough eggs. Red knots, which are an endangered species of shore birds, fly from Tierra del Fuego up to the Arctic. They time their migration so that 80% of the red knots are on the Delaware beaches when the horseshoe crabs are laying their eggs. This gives them the fuel to make the next leg of their migration up to the Arctic Circle. And they weren't getting enough eggs, so the weight of the red knots was going down and they weren't able to lay their own eggs. The numbers of red knots have been declining quite dramatically. They have voted to allow collecting the female horseshoe crabs again, which doesn't make any sense, except that there's demand for it.

What characteristics do you think have contributed to their long-standing survival throughout those hundreds of millions of years?

They've actually survived five major extinctions that wiped out the dinosaurs, a lot of marine animals, and all the larger animals, but what horseshoe crabs are able to do is, in the winter they go offshore and dig down into the sediments and then they don't eat, and they stay in the sediments for about six months and then they come out again. So, presumably during some of these extinction events they were able to just dig down into the sediments and wait it out and come back after the problems had passed.

Scientists preparing to extract blood from a horseshoe crab. Courtesy of Bill Sargent

What have you seen as far as a change in the population of horseshoe crabs since the bleeding practice began?

Just about this time every year, in the fall, we would walk along an 100-meter transect of the rack line and simply count the number of molts. I remember as a kid seeing lots of molts. When we went out in the year 2000, we’d only find two or three. Then, after the court case was won by the National Seashore and the ban was upheld, we went out and were seeing hundreds of molts along a 100 meter transect. It worked better than advertised simply by banning taking the horseshoe crabs from the shallow waters where they were mating, because essentially what the collectors had been doing is they had been taking the female horseshoe crabs out of the breeding population as they were laying their eggs. You didn't see the difference with the adult population, but it was the next generation that wasn't coming forward.

[Now], it looks like the same thing is happening, and it's because the pressure has increased so much because the demand for the horseshoe crab blood is so high because of COVID. All the COVID vaccines and the PCR tests all had to be tested to make sure they were free of pyrogens and the way they were doing this was with the horseshoe crab test. That's put pressure on the horseshoe crabs up and down the East Coast.

You've spoken to the East Coast population. Do you have an estimate of how the global population of horseshoe crabs is doing?

You only get the horseshoe crabs on the western side of oceans, and that's because you need a warm current. We have the Gulf Stream, which gives us a temperate climate up and down the East Coast. You get the same thing off of Asia. They have problems with water quality, they're also using them for lysate. So, they're probably in worse shape than we are on the East Coast.

Closeup of the ancient horseshoe crab. Courtesy of Soundwaters

What do you think the current outlook is for their population at this rate?

They're at a critical point now because you know the demand is still high because of COVID but that's going to come down pretty rapidly. You can use gene splicing to produce an artificial form of lysate that that wouldn't affect the live crabs. This was developed by a researcher in Singapore and there's some European companies that are using it, but the Food and Drug Administration in this country hasn't given permission for them to switch to the gene spliced form. I think the Food and Drug Administration will probably make the decision to have the gene spliced form [of the] horseshoe crab blood test as the standard test for pyrogens. So that will take pretty much all the pressure off the horseshoe crabs.