Researchers Study Stress On Horseshoe Crabs

By CBS Connecticut
18 May 2013

FAIRFIELD, Conn. (AP) — With their spiky, armor-plated shells, they look like miniature tanks mounting a surprise invasion on local beaches — except they have been at it for nearly a half-billion years.

But the American horseshoe crab, the homely, humble distant relative of ancient trilobites, has fallen on hard times. They’re harvested for bait, their blood is collected for medical science, and their numbers are dwindling in places along the Eastern Seaboard, as well as in Asia.

Sacred Heart University, which for years has studied the horseshoe crabs of Long Island Sound, has formed a partnership with Mystic Aquarium’s research arm to better understand the stresses facing the living fossils.

Mystic’s Sea Research Foundation is perhaps best known as home base for Dr. Robert Ballard, whose research team found the Titanic and the wreck of the USS Thresher in 1985. Ballard is the founder and president of the Ocean Exploration Center at Mystic Aquarium.

Officials with both Sacred Heart and the foundation said the link will benefit both institutions and will enable Sacred Heart to expand its Project Limulus, an ongoing effort to document the habits and movements of limulus polyphemus.

“The horseshoe crab is a very important animal globally, particularly in Asia,” said Steve M. Coan, Sea Research Foundation president and CEO. “We’re very excited to be working with Sacred Heart University. For our research team, it gives us an opportunity to expand our interests, and for SHU, we bring a number of assets to the table — we’re the largest living laboratory and the fourth-largest attraction in New England.”

He said the Sea Research Foundation is carrying out horseshoe crab research in Singapore.

“This will complement our existing efforts, and vice versa,” Coan said.

The project is also concerned with boosting public awareness worldwide of the horseshoe crab and its conservation.

The animal’s eggs and larvae are beneficial and even vital to shore birds and a host of marine animals. And its bluish, copper-based blood is used in the manufacture of nearly all injected medicines because it is used to test for bacterial contaminants.

Horseshoe crabs aren’t crabs at all. They’re more closely related to spiders, scorpions and other arachnids. Their ancestors appeared in the Ordovician about 440 million years ago, which makes them nearly twice as old as the earliest dinosaurs.

Horseshoe crabs have changed only slightly since then. Their larvae even look much like trilobites, a darling of fossil-hunters everywhere and one of their not-so-distant ancestors.

Part of the animal’s long-running success, according to SHU biology professor Jennifer Mattei, is its ability to endure varying degrees of brackishness, temperature and water oxygen levels.

“We thought that during hypoxia events (low oxygen episodes) in the Sound that they would go up to Rhode Island,” she said. “But from our tagging research, we found that they don’t move around all that much. They’re pretty hardy — they can tolerate some pretty low oxygen levels.”

Mattei was the impetus behind the new collaboration; she discussed the idea with Coan at a fundraiser some months ago. Both Mattei and the foundation are engaged in horseshoe research in the Far East, where numbers of three related species are in serious decline.

Horseshoe crabs are also proof that brainpower is not needed for survival. Millions of animal species have come and gone while the horseshoe crab has soldiered on relatively unchanged, despite making a few wrong turns here and there.

“At first, we thought that they always returned to the same beach, like sea turtles,” Mattei said. “But they’re not that smart, I’m afraid.”

Although the animal prefers a sandy beach for its eggs to successfully hatch, Mattei said females will try to lay eggs just about everywhere along the shoreline, from mud to concrete to lawns.

“We looked at that, and when they get the call to come up, they seem to think that everything’s a beach,” she said. “They’re completely instinct-driven. Eat and reproduce.”

Still, the animal doesn’t get a lot of respect. Countless thousands are killed every year by beachgoers, fishermen and oystermen out of ignorance. As for the collection of their blood by the drug industry, it was estimated that about 10-15 percent of the animals didn’t survive this ordeal. The industry maintains that the horseshoe crabs are treated with greater care now, and that the mortality rate from blood collection is down to about 3 percent.

“It’s true they’ll eat some of the oyster larvae,” Mattei said while on the Milford Point tidal flats on Wednesday, looking for horseshoe crab eggs. “But as you can see by the shells here, there’s no shortage of oysters that survive to maturity.”

She said that the collaboration with SRF will likely double the number of graduate students in her program, and there will be more undergraduate interest as well.

Mattei has been studying the horseshoe crab in Long Island Sound for more than a decade, tagging and tracking scores of the hat-sized animals with the help of her students and others as part of her long-running program, Project Limulus.

There are 18 Connecticut-licensed horseshoe crab harvesters in the state. Horseshoe crabs are used as bait to attract eels, a delicacy in Asia. Mattei said their numbers seem to be holding in the Sound, despite this culling activity.