Biologist Works to Restore Horseshoe Crab Populations

When it comes to human medicine, horseshoe crabs are lifesavers.

Their blood cells contain a clotting agent that attaches to harmful bacteria. This “miracle blood” is widely used by pharmaceutical and medical companies to ensure that their products, e.g., intravenous drugs, vaccines and medical devices, are free of contamination.

So when the horseshoe crab population became threatened in North America and Southeast Asia about a decade ago, Mark L. Botton, Ph.D., professor of biology, took notice. Botton has been studying the horseshoe crab since the mid-1970s and is now one of the country’s leading researchers.

There are four species of horseshoe crab with habitats in North America and Southeast Asia. Factors such as pollution and coastal development have threatened the prime beach areas they need to thrive.

In the United States, Botton said, a major upswing in the commercial fishing industry in the 1990s threatened the animals, which were found to be a highly effective bait for eel and especially conch, a sea snail that is popular as a cuisine in the Far East.

“Here were these really interesting animals that had been around for 400 million years, and now man-made activities might be pushing some of them to the brink,” he said. “There were a lot of alarm bells going off.”

One alarm bell that Botton certainly noticed was that the shrinking population of the American horseshoe crab, known as Limulus, on New Jersey’s Delaware Bay. That bay area was where Botton, as a young doctoral student at Rutgers University in the mid-1970s, first encountered the animal.

“I grew up in Brooklyn and had seen a couple of them in Jamaica Bay, but I had never seen literally thousands of them mating, appearing like cobblestones along the beach,” he said. “Night after night we’d see this incredible thing.”

Botton and his colleagues began collaborating on research and publishing articles about the threat in scholarly journals. He also helped plan an international conference held in 2007 at Dowling College in New York. The conference resulted in a book, Biology and Conservation of Horseshoe Crabs(Springer, 2009), which he co-edited.

These efforts, coupled with the advocacy by the Delaware-based Ecological Research & Development Group (ERDG), have resulted in good news for the Delaware Bay population of horseshoe crabs, which has shown some sign of recovery, Botton said.

“Environmental protections in the United States are among the strongest,” he said. “The harvesting of horseshoe crabs for bait fishery has really been clamped down on by state and federal regulations … and these have really stopped the bleeding for the population in Delaware Bay.”

The jury is still out, however, when it comes to horseshoe crab populations elsewhere in the United States.

“Since there is still a need for horseshoe crabs in the bait fishery industry, and to obtain the animal’s blood for biomedical testing, some of the pressure that used to be in Delaware Bay has shifted to locations further to the north and south,” he said.

“While they’re not ‘threatened’ in the legal sense [of the federal Endangered Species Act], there is certainly cause for concern because some of these other bays do not have as many horseshoe crabs as Delaware Bay,” he explained, “and evidence from tagging and genetic markers suggests that some of these smaller populations may be functionally isolated from the larger mid-Atlantic stock.”

While the smaller, more isolated populations in the United States may be less capable of withstanding fishing pressure, discussion and research that began at the conference about habitat preservation and the possibility of aquaculture—raising the eggs in captivity to try and replenish the population—continues.

“People have done this for years and years in freshwater environments—trout hatcheries, for example, but now there are some people from a variety of countries who are at least exploring if it’s feasible to do this with horseshoe crabs,” Botton said.

Meanwhile, the horseshoe crab populations in Southeast Asia and Mexico are in peril, he said.

“Hard numbers are not available, since it is only recently that people have conducted surveys of the horseshoe crabs in Asia, but it was clear from the 2007 conference that my Asian colleagues all felt that their populations had declined,” he said.

At that conference, habitat loss, water pollution, urbanization and land reclamation were named as factors affecting the horseshoe crab populations in parts of Taiwan, India, China and Mexico, Botton said.

“There is no international treaty or anything like that to protect horseshoe crabs. In a lot of these places, it’s not perceived as an important task to preserve them,” he said.

“When you ask what society wants to get out of coastal zones, you have housing and recreational interests, industrial interests, and in places like Mexico, you have a huge oil industry in the Gulf,” he said. “There are a lot of different players, and sometimes the preservation of environment and species take a back seat to economic forces.”

Perhaps this is why educating the public is a crucial component for the conservation of horseshoe crabs.

“We had various people at our conference from Southeast Asia talking about trying to raise public awareness about the value of horseshoe crabs because people aren’t going to just get excited about preserving something if they don’t understand its ecological role or importance,” Botton said.