Bleeding out: why the horseshoe crab's medicinal value may be a threat to the species

Horseshoe crabs are ancient marine creatures that look more like the hoof of a horse than your standard snow crab.

They've been around for almost half a billion years — and in that time, they've developed a powerful, internal mechanism to protect themselves from infection.

When bacteria sneaks past a horseshoe crab's shell, cells in the crab's baby blue blood send out a chemical that clots around the invader.

When humans discovered this biological superpower, biomedical companies started draining their blood. The substance they create with is called Limulus Amoebocyte Lysate (LAL). It's used to detect bacteria such as E. coli in things such as implants, vaccines, and medical implements.

If you've ever been to a hospital, there's a good chance you've benefited from this process. 

LAL requires a lot of blood and because the clotting property is unique to horseshoe crabs, it's one of the world's most expensive liquids. One gallon can cost as much as $19,000 CAD.  

As the University of New Hampshire's Win Watson tells Day 6 guest host Rachel Giese, the bleeding is hurting the species.

"There is some mortality associated with it and once they release them into their natural habitat it's hard to know if there's additional mortality," he says.

Watson is a professor of animal neurobiology and physiology. He's been studying horseshoe crabs more than 40 years and says attention on the creatures has really grown over the past decade.

"Because of the heavy fishery on horseshoe crabs, both for this biomedical bleeding process and as a bait in some places, there's concern that ... numbers are declining."

Bleeding and returning the crabs

Meghan Owings is a grad student who works with Watson. Her work focuses on the impact of biomedical bleeding on horseshoe crabs.

"Several different studies have documented about [a] 10 to 30 per cent mortality rate, which is pretty significant," she says.

Her goal is to understand exactly how many crabs are affected by this process and to advise companies like Associates of Cape Cod, Lonza, Wako Chemicals, Charles River Endosafe, and Limuli Labs on how to better protect the animals.

There's definitely some ways that we could change their process.- Meghan Owings

Her research requires her to put the crabs through the exact same process that the biomedical companies do.

That means collecting fresh crabs from the ocean, exposing them to heat, sunlight and air — and of course, removing a substantial amount of blood.

"We are limited — or biomedical companies are limited — to about 30 per cent of their body weight, theoretically," says Chris Chabot, a professor at Plymouth State University who works with Owings and Watson.

In addition to bleeding the crabs, Owings spends a lot of time with them in her car.

"We try and do it as if we're taking them back to a facility," Owings says of the four-hour drive she makes with the crabs in tow.  

"We go to the beach, we do some errands. We go all along the coastline," she jokes, adding that her car still smells like her arthropod companions.

In total, horseshoe crabs can spend as much as 72 hours out of the water.

Monitoring the crabs

Before returning the crabs to their natural habitat, Owings equips them with accelerometers. This is so she and her colleagues can monitor their movement after the bleeding. 

Owings says the blood loss and exposure to heat and air affect the biorhythms of the horseshoe crabs. 

"We have seen them switch from either a tidal to a daily rhythm or they've completely lost their rhythm."

Crabs use the rhythms to find food and mating beaches. If they're knocked out of whack, the crabs can miss a whole mating season.

And as Watson points out, it also affects the bird population.

"[The crabs] lay a whole bunch of eggs along the east coast of the United States every spring and the migrating birds depend on those eggs to be able to replenish their energy supplies."

"If the horseshoe numbers decline, then the eggs decline, [and] then the birds decline."
                                            

Advice for biomedical companies

As for alternatives, Watson says there aren't any.

"I hope that sometime soon, someone figures it out. But in the meantime, this is the most cost effective way to do it."

That makes the research he's doing along with Owings and Chabot all the more important.

"There's definitely some ways that we could change their process," Owings says of the advice she will give the biomedical industry.

"Whether it's having all of the companies keep the horseshoe crabs moist, or making temperature regulations where they have to keep the horseshoe crabs between 60 and 70 degrees when they keep them overnight."

She says she and her colleagues are looking at a food supplement that the biomedical facilities could feed the crabs to boost their hemocyanin levels.

"The end goal is to make it a more sustainable practice for the horseshoe crabs," she says.

"Hopefully [the companies will] understand and take on some of advice," she says. "That will make it worthwhile."
 

To hear the full interview with Win Watson and Meghan Owings, download our podcast or click the 'Listen' button at the top of this page.