March 8, 2023
Horseshoe crabs are an ancient species, having survived five mass extinctions over hundreds of millions of years. However, human exploitation may finally wipe out this resilient species if recent trends continue. As a recent article by science investigator Deborah Cramer in The New York Times notes, horseshoe crab populations have experienced significant decline in East Asia and the United States, partially due to fishermen who kill them to use as food or bait. Another major contributor to this decline is the use of their blood for endotoxin testing. Endotoxins are contaminants in pharmaceutical products that can be lethal to infected patients. Pharmaceutical companies must run extensive testing on implants and injectable medicines using a chemical called limulus amebocyte lysate, which can detect the toxins by reacting with them. This chemical is sourced from horseshoe crab blood; about 700,000 horseshoe crabs are captured in the United States each year to have their blood drawn for endotoxin tests. This process can kill up to 30% of the horseshoe crabs and prevent some from laying their eggs on the shore.
The International Union for the Conservation of Nature classifies horseshoe crabs as an endangered species in New England and a vulnerable species on many parts of the East Coast. To combat this population decline, some drug producers like Eli Lilly have been working on a transition toward the use of rFC, a more sustainable and seemingly more reliable alternative to limulus amebocyte lysate. However, manufacturers are still waiting on the US Pharmacopeia to set legal standards for rFC use. The USP lags behind similar regulators in Europe and Japan in this process. The organization’s approval of rFC standards will be a necessary step toward reviving diminished horseshoe crab populations and those of other species, like red knots, that depend on them.