Horseshoe Crabs

Published: Thursday, July 11, 2013 at 09:41 AM.

Horseshoe crabs have been used by humans in many, and sometimes surprising, ways. The tail was once used by Native Americans for spear tips and awls to punch leather. In the 19th century, horseshoe crabs were dried and ground for use as fertilizer or poultry feed supplement. In 1856, 1,200,000 horseshoe crabs were harvested on just a one mile stretch of Delaware beach. As late as the 1920’s and early 1930’s, 4-5 million crabs were harvested annually. Harvesting horseshoe crabs became unprofitable with the use of artificial fertilizer and the reduced crab population.

The horseshoe crab has new value however. The creature has pale blue blood that contains an agent valuable to medicine. The active agent is called Limulus amoebocyte lysate. It can be used to detect extremely small amounts of endotoxins, which are poisons found in a major class of bacteria that cause serious infections in humans. The value of the Limulus lysate test is that it detects smaller amounts of endotoxins quickly and reliably. If you have ever received an injection of a drug or vaccine, the batches were tested with Limulus lysate to ensure no bacterial contamination. To obtain the lysate, horseshoe crabs are bled by inserting a needle into the heart chamber. The donor crabs are released afterwards. Additionally, chitin from horseshoe crabs is used to create a suture material. Chitin-coated suture material reduces healing time by 35 to 50 percent. Horseshoe crabs contribute formidable weapons to medicine’s arsenal against infectious disease.

Meanwhile, the horseshoe crab continues its silent shuffle across warm shallow seas as it has done for millions of years, and with care for our bays and estuaries, it will continue to do so.

Tom Baird has been a fisheries biologist, high school and community college teacher (oceanography and microbiology), director of a science and environmental center, teacher of science and principal in Pinellas County as well as an educational consultant. He retired from the Florida Department of Education and he and his wife divide their time between Tallahassee and Cape San Blas.

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