I hear horseshoe crabs are used for medical testing. Are they killed?
No, they are returned to sea. Studies do show, however, a mortality of three to 15 percent in captured horseshoe crabs, but much depends on the care the animals receive. They do well as long as they are kept cool and moist. Many horseshoe crabs are recaptured with no harmful effects.
The crabs are collected in both deep and shallow water using rakes or dredges. They are placed in a dark, refrigerated truck and transported to a lab, where nearly one-third of the crab’s blue blood is removed. The crab is returned to the sea and recovers fully in about a week.
The medicinal value of horseshoe crab blood comes from its ability to clot in the presence of bacteria, rendering the bacteria harmless. Even though bacteria are usually destroyed by modern sterilization techniques, some bacteria, called endotoxins, may survive the sterilization process. This blood-clotting ability of the horseshoe crab makes it very valuable in testing for injectable medicines, vaccines and sterile medical equipment.
It’s interesting to note that horseshoe crabs live in an environment teeming with bacteria, and, like many invertebrates, lack an immune system. In such an environment even small injuries should be fatal. Yet, horseshoe crabs have survived millions of years.
The horseshoe crab has also proved valuable to the medical field in another way. Studies involving the nerve pathways in the eyes of horseshoe crabs have led to many discoveries in human eye research. The outer shell of a horseshoe crab is made primarily of chitin. Scientists discovered that when used as a coating for suture material and burn dressings, chitin rapidly increased wound healing, cutting the time by half.
Unlike human blood that is iron based, horseshoe crab blood is blue because it is copper based. The contributions they have made to human medicine have saved countless lives.
Horseshoe crabs also play an important role in the marine food web, providing nutrition to large numbers of migrating fish and shorebirds. They are used as bait and in effect support a large commercial conch fishery in the northern United States.
Unfortunately, horseshoe crab populations are dwindling due to habitat loss, water pollution and over fishing. Efforts are now being made to reverse this trend. Losing the contribution of this one animal could prove devastating, not only to birds and marine life, but humans as well.