The Blood Harvest

The horseshoe crabs are returned to the ocean a great distance from where they were initially picked up to avoid rebleeding animals. The whole process takes between 24 and 72 hours.

The industry says that not that many of the animals die. Between 10 and 30 percent of the bled animals, according to varying estimates, actually die. We can imagine that it's like us giving blood. The crabs get some apple juice and animal crackers and are fine soon thereafter. 

But some people have noticed problems. In the regions where horseshoe crabs are harvested in large numbers for biomedical purposes—like Pleasant Bay, Massachusetts—fewer and fewer females are showing up to spawn. Perhaps the bleeding was, to use a technical term, messing them up, even if it wasn't killing them.

Researchers at the University of New Hampshire and Plymouth State University decided to test this hypothesis. They attached accelerometers to female horseshoe crabs that had been bled for our benefit. 

A horseshoe crab outfitted with an accelerometer
(Win Watson, University of New Hampshire)

They reported their results in a new paper in The Biological Bulletin, "Sublethal Behavioral and Physiological Effects of the Biomedical Bleeding Process on the American Horseshoe Crab, Limulus polyphemus.

The bleeding process appears to make the bled animals more lethargic, slower, and less likely to follow the tides like their counterparts do.

"The changes we observed in activity levels, movement velocity, and expression of tidal rhythms may interfere with daily L. polyphemus activities, which would be particularly pronounced during the spawning season," they write. "Spawning necessitates several energetically costly trips to the intertidal zone larger females tend to make more excursions to the intertidal zone, often making multiple trips within the same week. An activity deficit, such as that caused by biomedical bleeding, may influence either the number of those trips or their timing. In the case of the latter, females may delay spawning activity while they are recuperating, and this could reduce their spawning output."

In short: Bleeding a female horseshoe crab may make it less likely to mate, even if it doesn't kill it. (Only 18 percent of the crabs the authors tracked died.)

While the bleeding process is clearly better for the crabs than the outright harvesting that used to occur, the study shows that there's no such thing as free horseshoe crab blood. 

The logical question to ask is: Why hasn't a synthetic substitute for LAL been developed? After all, it's not like we still get insulin for diabetics from pigs. We use yeast to produce it using the DNA sequence that codes for the protein. 

It turns out: Companies are researching this solution. They don't want the precursor of their product to be regulated by a Fishery Management Plan, if they can avoid it.

In particular, biologist Ding Jeak Ling from the National University of Singapore succeeded in producing the key bacterial detection enzyme, known as Factor C, in yeast. She licensed the process to Lonza, which has brought it to market as a product called PyroGene. A German company named Hyglos has been working on another synthetic endotoxin detector, too. Other, even more advanced technologies are on the way, too.

So, good news for the horseshoe crab! It's like when we struck crude oil and sperm whales celebrated (at least in the imagination of a Vanity Fair cartoonist). 

The cosmic joke might be that horseshoe crabs, which for the past 30 years have been a high-value part of the new biotech economy, will return to their previous status as fishermen's bait for predatory snails. Being valuable alive has obviously hurt the horseshoe crab in some ways. But having no economic value at all is worse.

Horseshoe crabs are an ancient animal, more than half a billion years old. They have their own ways of doing things, a fact we've been exploiting for decades. Their blue blood? That's because copper plays the role in the crabs' blood that iron does in ours. The iron-based, oxygen-carrying hemoglobin molecules in our blood give it that red color; the copper-based, oxygen-carrying hemocyanin molecules in theirs make it baby blue. 

Our own species evolved a thousand times more recently, coming into our current anatomical form a couple hundred thousand years ago. Let's hope we don't wipe horseshoe crabs out after we finish cloning their ancient chemical wisdom. 

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