Horseshoe crabs along the US East Coast are being put at risk of population decline because of systematic crab-bleeding operations done by the pharmaceutical and medical device industries, according to new research that suggests that even though the horseshoe crabs are released after being bled, the bleeding process alters their behavior and psychology.
Horseshoe crab blood has the unique property of being able to sterilize a class of endotoxins that other compounds cannot. Without horseshoe crab blood, it would be difficult to ensure that intravenous drugs, vaccines, and medical devices are free of bacterial contamination. As such, the blood of the horseshoe crab is in high demand, and substantial harvesting operations are in place.
Horseshoe crab blood is most notably used to manufacture Limulus amebocyte lysate (LAL), which is used to ensure vaccines and medical equipment are free of bacterial contamination. The only known way to produce LAL is with horseshoe crab blood, the researchers said.
In the past, the practice of harvesting the crab's blood and returning them to the wild has been considered safe and sustainable, but the new research questions that position.
"The crabs are very heavily bled - about 30 percent or more of their blood is taken, and that's a fair amount," said study co-author Chris Chabot, a professor of neurobiology at Plymouth State University. "Approximately 20 to 30 percent of those crabs do not survive, so we were curious if any of the surviving crabs experienced nearly lethal effects from the bleeding."
Chabot's collaborators included study leader Rebecca Anderson, a PSU graduate student, and Win Watson, a University of New Hampshire professor of zoology. Writing in The Biological Bulletin, the research team reports that for about two weeks after the bleeding procedure, the crabs' behavior differed from their behavior prior to the bleeding. This was measured by taking wild crabs in the lab, fitting them with monitoring devices for one week, then harvesting their blood and continuing to monitor the crabs for signs of change.
After being bled, the crabs behaved as if they were disoriented for nearly two weeks, the researchers found. The research team wants to repeat their study in the wild to see if the same results occur. If they do, it could lead to new standards and regulations for horseshoe crab blood harvesting.
"If the biomedical industry could delay the blood harvest, it would probably help these animals," Chabot said. "For example, if they are bled after the breeding season, then they could recover in the subsequent months, fatten up and survive the winter without any problems to be able to breed again the following year."
Currently, the crabs are harvested when they beach themselves to breed, where it is easy to capture them. "If the crabs are bled and then returned to the beach in a disoriented condition, they might be less likely to breed. This has the potential to exacerbate the population declines that are already occurring in parts of the east coast, including Delaware and Cape Cod," the University of New Hampshire said in a statement.
Additionally, the conditions in which the crabs are transported could be improved as well, the researchers said. The standard practice of hauling the crabs out of water and delivering them to a harvesting facility while in a state of stress and suffocation could be changed to a water-based transfer.
"If instead they were kept in cold, well-aerated water and perhaps fed, their stress levels might decrease and thus improve their chances of survival and ability to breed upon return to their native habitat," the researchers said.
"We want to ensure that the biomedical bleeding is a sustainable practice, because horseshoe crabs are a critical component of the coastal ecosystem," Chabot said.
Study leader Anderson added: "I hope that this research helps to design management regulations that meet the needs of both the people and the crabs."