Harvesting horseshoe crabs’ distinctive blue blood. Credit: National Geographic/Getty Images


By Lindsay Albright


Dead horseshoe crabs along Slaughter Beach in Delaware Bay. Credit: Jessica Quinn

You’re only 3 years old when you and your father pack up the car to go to the beach. You aren’t quite sure what all this talk is about surf fishing, but you will soon find out it’s a technique for catching fish by standing on the shoreline or wading in the surf. Your father meets up with his surf fishing friends and proudly introduces you. As the group walks along the shore searching for fish, your father gives you a very important task. He instructs you to flip those alien-like creatures on the sand who got stuck on their backs right-side up and float them back into the ocean. At the time it feels like you’ve been given a responsibility as big as holding the world itself together — and in a way you have been. One by one you begin flipping the mysterious horseshoe crabs over and watch them hurry back into the ocean — all the while imagining them giving you a little “thank you” before they leave. Your dad’s friends tell you to do the opposite, to just kill them, or let them die. What do crabs matter anyway? But without hesitation your father says, “No. Put them back in the water.” From that day, you have never stopped working to save the horseshoe crabs, and you know better than anyone just how much this mysterious species matters to us all.

This unforgettable childhood experience is how Allen Burgenson was first introduced to the ancient world of horseshoe crabs, a 450-million-year-old species whose rare blue blood is used in the biomedical industry to test pharmaceutical products for safety. A species that, although vital to human health, is threatened with extinction. A species that Burgenson wants to make the world aware of, so we can work to protect and save them.

Now a global expert in biomedicine working for Lonza Pharma and Biotech, Burgenson agreed to an interview with Q Magazine. During the interview, Burgenson discussed how horseshoe crab blood is used, the vital importance of this species to biomedicine, and the serious environmental threats facing the species today.


Ancient Background

In preparation for the interview, I tried to find out all I could about this extraordinary crab species, including how they’re being used in the biomedical industry, and why their existence is threatened. What I found along the way is that horseshoe crabs may be crucial in developing a vaccine for the virus currently plaguing the world — COVID-19.

A horseshoe crab fossil. Credit: blog.nature.org

Prehistoric invertebrates, horseshoe crabs have crawled this planet since before the dinosaurs. They have survived three of Earth’s five official extinctions, outlasting drastic environmental changes and volcanic eruptions largely thanks to their flexible diet and ability to tolerate different habitats.

Horseshoe crabs certainly look prehistoric, even alien. A horseshoe crab has ten legs, nine eyes, and enjoys its own taxonomic class — Merostomata — which means “legs attached to the mouth.” While their name and appearance suggest crab, they are actually closer relatives of scorpions and spiders.

Four species of the horsehoe crab exist today, one along the eastern coast of North and Central America, and the other three along Asian coasts in the Indian and Pacific Oceans. The American crab Allen Burgenson flipped over at age 3 is named Limulus polyphemus, which breeds along the East and Gulf coasts in late spring and early summer.

The crab’s journey from the deep ocean begins with parent males arriving first, followed by the females. Breeding usually takes place during new and full moons, when the females lay their eggs on the beach in small holes they dig in the sand. The males then fertilize the eggs. The females can lay tens of thousands of eggs, most to be eaten by birds, reptiles, and fish. Those eggs not eaten will hatch in about two weeks and then move into ocean tidal flats for about a year until they mature and can migrate into deeper waters. Juvenile horseshoe crabs will molt up to 17 times over the next 10 years until they reach adulthood, which can last another decade.

Horseshoe crabs play an important role in their ocean ecosystem, as a keystone species. They are a food source for many species of shore birds — many of which feed on horseshoe crab eggs during their migratory routes. Flocks of red knot birds, for example, migrate from southern South America all the way to the Arctic. During their journey they stop in the Delaware Bay area to gorge on horseshoe crab eggs, their last meal before the Arctic. In the past, the United States has used horseshoe crabs for fertilizer, resulting in a decline in horseshoe crab populations. When horseshoe crab populations began to decline, so did those of the red knot. Threats to the horseshoe crab ripple through the entire Atlantic seaboard ecosystem.

How is it that this odd creature, 450 million years old, could be of such importance not only to the red knot bird, but to medical researchers seeking a cure for COVID-19? Answer: It’s all in their blood. Horseshoe crabs have blue blood, not red. This is unusual in and of itself, but it’s what the crabs’ blood can do that makes it so special.


Blood Bonds

If you’ve ever gotten a shot of any kind, you can be sure the drug was first tested for safety using the blood of horseshoe crabs. Every drug or medical device that comes into contact with our bloodstream must be tested for bacterial endotoxin, deadly to humans. The blue blood of horseshoe crabs is very sensitive to endotoxin, and thus a vital resource for drug testing.

The ingredient in the blood of horseshoe crabs used to test pharmaceutical products is called Limulus amebocyte lysate, or LAL. Burgenson, who has worked with LAL for almost 40 years, explained to me the process of collecting and using horseshoe crab blood in the U.S.-based biomedical industry. First, fishermen collect the crabs and bring them to the bleeding facility where they are cleaned. Next, their blood is taken in a process not unlike when people donate blood. When a horseshoe crab is bent in half, a small membrane is exposed in the cardiac sinus. The lab tech wipes the area with iodine and inserts a clean needle, through which about three to six tablespoons of blood are removed from each horseshoe crab. After the bleeding process they are put into a return bin and checked, after which contracted fishermen restore them to the ocean within 24 hours. Although the Atlantic States Marine Fisheries Commission associates a 15% mortality rate with this process, Burgenson claims this rate is based on old data; today the bleeding practice mortality is reported to be more like 3-5%.

Back in the lab, technicians combine the extracted blood with anticoagulants so it doesn’t clot, and put it into a centrifuge where the cells fall to the bottom. Although humans have many kinds of blood cells, horseshoe crabs only have one: amebocytes. The amebocytes are spun down, which separates the blue liquid — the blue hemolymph — which is then poured from the centrifuge. The remaining amebocyte cells are added to several other proprietary formulations, then freeze-dried and incubated at 37 degrees Celsius for one hour. This process results in the final LAL product: to test for endotoxins in injectable pharmaceuticals and medical devices.

The ability to test for endotoxins is critical to the past, present, and future of human health. Endotoxins, which exist in bacteria, can be what medical professionals call “pyrogenic,” which means they provoke a negative, toxic, usually feverish response in the body. Burgenson explains that there is a paradox here in that our guts are full of endotoxins, which are pyrogenic in nanogram amounts. One billionth of a gram of endotoxin is enough to cause a fever, and higher amounts will cause people to go into shock and potentially die. Pharmaceutical products can become contaminated with endotoxins from the water used to produce these products, and therefore all injectable drugs must be tested for endotoxins before being injected into patients. And what a successful system it is! Burgenson points out that in the 40 years LAL has been on the market, there’s never been an instance where a product that tested negative for endotoxins using LAL turned out to be positive when the product was used out in the field.

“If you think of all the millions of product batches that have been manufactured around the world and tested with LAL it has never missed a bad batch of pharmaceutical products. Every person who has ever received an injection — whether it be a vaccination, whether it be IV fluids, whether it be vitamins — anything that’s ever been injected into anybody in the world — everybody — that product that was injected into them has been tested using LAL. Every person in the world has been touched by the horseshoe crab. I think that’s pretty amazing.”

Before LAL, hundreds of thousands of rabbits were used every year for pyrogen testing. Rabbit testing didn’t gain popularity until 1941, when injectable pharmaceutical drugs were being tested and used for World War II. Before then, anytime someone was injected they could expect something called “injection fever,” meaning that one time in 10 someone given an injection could expect to become sick, or possibly die, due to endotoxins.

In 2020, we are in a mad rush to find a vaccine, cure, or treatment for COVID-19 and to bring it to the market as soon as possible. Any vaccine or injectable drug created in hopes of finding a cure or treatment will therefore be tested using the LAL product derived from the blood of horseshoe crabs, making this species crucial in our fight against this virus. The horseshoe crab has survived for more than 450 million years, and it’s truly incredible to think how a prehistoric species can be used in modern medicine to help us. Yet we that benefit most from the horseshoe crab also represent a direct threat to its existence. Can a species that survived for millions of years through multiple extinction events survive what is now known as the Anthropocene era?


Crabs on the Brink

Credit: asmfc.org

Of the four species of horseshoe crabs, the three Asian varieties have been just about fished to extinction. The biomedical industry there is likewise dangerously careless. Horseshoe crabs are not bled minimally and returned to their natural habitat, but fully drained of blood, killed, and then ground up for fertilizer, used in traditional medicines or, occasionally, eaten for dinner (Burgenson described the amount of meat found on horseshoe crabs as “spider meat” because there really isn’t much to eat when you take into account a horseshoe crab’s physiology). Until countries such as China, Vietnam, Thailand, Malaysia, Singapore, and Indonesia come to some agreement, the black market in horseshoe crabs will continue to kill off and endanger this vital species.

By contrast, the United States has the Atlantic States Marine Fisheries Commission — Burgenson is the chairman of its Horseshoe Crab Advisory Panel — which regulates horseshoe crab fisheries by strictly enforcing quotas in the bait industry. If a fishery exceeds the quota it runs the risk of losing its license. Unlike the biomedical industry’s treatment of horseshoe crabs, mortality in the bait industry is 100% because the crabs are chopped up as bait to catch eels, conchs, and whelks.

The difference between how the two industries utilize horseshoe crabs is that the biomedical industry collects horseshoe crabs, whereas the bait industry harvests them. “When you harvest something, you kill it. We don’t kill. We take the blood and then we put it (the horseshoe crab) back,” Burgenson says. “Have you ever seen those big paper cutters that they used to have in schools?” I thought back to art class in high school where the teacher used one to cut stacks of paper and poster boards. “Well (bait fishermen) have those on their boat and then they put a horseshoe crab in this big paper cutter, and they cut it in half and cut it in quarters, and then they put it in their traps and let it go. A lot of times the horseshoe crabs are already dead … sometimes they’re not.” A species whose blood is crucial in the testing of vaccine safety lives in a world where they are chopped up in quarters and thrown into the ocean to be used as bait.

The bait industry affects populations of horseshoe crabs, but so do other fisheries through bycatch. Thousands of horseshoe crabs are unintentionally caught up in nets designed for flounder and other marine staples. Too often commercial nets come up full of horseshoe crabs, half of which are destined to perish. The third major threat to horseshoe crabs, Burgenson says, is loss of habitat. Have you ever wondered what the newly arrived piles of rocks along your favorite beaches are for? Rock walls serve as erosion control in an age of rising seas, but in doing so cause devastating harm to horseshoe crab populations. When crabs come to the shore to spawn, they get stuck and die trying to climb over the rocks. An example of this is seen in Delaware Bay on Slaughter Beach where the entire shoreline is lined with rocks to prevent beach erosion. If you visit this beach during their spawning season, you will find tens of thousands of stranded, dead horseshoe crabs.

The future for a species that’s been around for more than 450 million years may seem bleak, but there is hope. Bad fishing practices are not without consequences. Southern states, such as South Carolina, have eliminated the bait industry by making it illegal to fish for horseshoe crabs with the intention of using them as bait. The only purpose of catching horseshoe crabs in these locations is to use them for the production of LAL, and because of this horseshoe crab populations are increasing along the southern East Coast. Populations of horseshoe crabs near Cape Hatteras and further south are actually doing quite well due to the elimination of this species being lost in the bait industry. Likewise in Mid-Atlantic states, populations of horseshoe crabs are stabilizing thanks to regulations put in place to reduce quotas. However, it’s the New York Bight area — from the Delaware Bay to Montauk Point, Long Island — where the populations of horseshoe crabs are decreasing at an alarming rate due to illegal poaching.

Some eel and conch fisheries have also tried to work their way around the new protective regulations. A few years ago these fisheries began importing horseshoe crabs from Asia. In doing so they introduced an invasive species that posed a biological threat to native horseshoe crabs through exposure to foreign diseases. It wasn’t long, however, before horseshoe crab advocates such as Burgenson stepped in and made it illegal to bring Asian crabs to the United States. Thanks to their actions this threat to the Limulus polyphemus species has subsided, but it goes to show how determined the bait industry is.

Credit: Amanda Sherman

Nearing the end of our interview, I asked Burgenson what he would say if he could tell people just one thing about horseshoe crabs: “The one thing people have to know is that the horseshoe crab has touched everyone’s life no matter where you live. They are responsible for maintaining human health around the world.” His message to people in Asia: “Stop killing them.”

The fact that a species — a species so resilient that it’s survived major extinction events and has been around for more than 450 million years — can be at risk of extinction due to human actions goes to show just how much our global civilization impacts the natural world. If we’re capable of posing so big a threat to one of the world’s most resilient species, what does that mean for species out there who aren’t as tough?

Ask yourself: Who will you be? Will you be an Allen Burgenson who helps save the horseshoe crab and its habitat, or will you be like his father’s thoughtless friends wanting him to kill them? The next time you get a vaccine, for COVID-19 or anything else, remember you owe the safety of that vaccine to a 450-million-year-old creature with precious stores of blue blood.

About the Author …

Lindsay Albright is from Columbia, Md. She graduated with a degree in Earth, Society, and Environmental Sustainability and received a minor in Creative Writing and the Certificate in Environmental Writing (CEW). This piece was researched and written for ESE 498, the CEW capstone course, in Spring 2020.