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.
