(Photo credit: Eurypterids.net)
Walking the shores of Buzzards Bay this past weekend, I was struck once again by the changes that have taken place here since my childhood. Drifts of eelgrass line the high tide line once more: a rare sight just a decade or so ago after a massive die-back of our still depleted grass beds. Even higher mounds of slipper shells are so abundant along this stretch of coastline they tinge the cobble beach a dusty rose. On the other hand, I found just one fragment of horseshoe crab shell, and cannot remember the last time I saw a live one in the water.
The four living species of horseshoe crab represent one of nature's most ancient designs. Limulus polyphemus, found in the North Atlantic shallows from Maine to Mexico, has remained virtually unchanged since it evolved an estimated 400 million years ago. They survived the great Permian-Triassic extinction event which was especially catastrophic for marine organisms, and two subsequent major mass extinctions (the Triassic-Jurassic 200 million years ago and the Cretaceous–Tertiary event 65 million years ago that brought an end to the dinosaurs). In all that time, continents rose and fell, ash and ice covered the land, yet these primitive relatives of spiders and scorpions survived it all. Even more remarkably, they did so without the benefit of an immune system. What they had instead has made them incredibly valuable, and today places this species previously considered only good for bait at ultimate risk.
Horseshoe crab blood sells for $15,000 a quart. It also happens to be bright blue because it is copper, rather than iron-based, but what makes it really special is a remarkable adaptation that compensates for the crab's inability to produce antibodies. Horseshoecrab.org tells us how:
"As we know, seawater is a virtual 'bacterial soup'. Typical near-shore areas that form the prime habitat of the horseshoe crab can easily contain over one billion Gram-negative bacteria per milliliter of seawater. Thus, the horseshoe crab is constantly threatened with infection. Unlike mammals, including humans, the horseshoe crab lacks an immune system; it cannot develop antibodies to fight infection. However, the horseshoe crab does contain a number of compounds that will bind to and inactivate bacteria, fungi, and viruses. The components of LAL are part of this primitive "immune" system. The components in LAL, for example, not only bind and inactivate bacterial endotoxin, but the clot formed as a result of activation by endotoxin provides wound control by preventing bleeding and forming a physical barrier against additional bacterial entry and infection. It is one of the marvels of evolution that the horseshoe crab uses endotoxin as a signal for wound occurrence and as an extremely effective defense against infection."
Since the 1960s, when researchers at the Woods Hole Oceanographic Institute - located down at the mouth of the Bay - first isolated the compounds in horseshoe crab blood that respond to bacteria, an extract has provided the most reliable test used by the pharmaceutical and medical device industries to detect sterilization resistant endotoxin bacteria. This has been extraordinarily important for human health, but it has been hard on the crabs.
My sister had a summer internship at Chatham's Pleasant Bay in the 1980s where she studies the effects of harvesting on its horseshoe crab population. It is possible to harvest horseshoe crab blood by syringe without killing the animal (anywhere from 3%-15% mortality has been recorded and up to 30% of the animal's blood is taken each time), but over harvesting and excessive extraction have combined to produce crashes in local Atlantic horseshoe crab populations from Delaware to Cape Cod. It doesn't help the species that it swarms breeding beaches during the full moon in late Spring and can be easily gathered in shallow water with clam rakes and dredges. In some areas, there are no longer enough horseshoe crabs in the environment to support bird species like the Red Knot that depend on their eggs as an important food source. According to A DC Birding Blog, New Jersey now bans horseshoe crab harvesting and Massachusetts plans to cut its quota in half. The Cape Cod Times had a story last April that reported:
"Massachusetts' current horseshoe crab quota is 330,377 annually, second only to New York's at 366,272. Delaware is one of the states that has cut back its harvest, setting its quota at 100,000. Delaware harvested 76,663 horseshoe crabs last year, a more than 75 percent drop from 2003.
In Massachusetts, about 70,000 animals were landed in 2004. That more than doubled to 150,000 last year. Most of the increase was shipped out of state by bait dealers.
A spokeswoman for the state Executive Office of Environmental Affairs would not specify yesterday exactly what the new regulations would be but said the limit would be about 150,000, the same as landings for last year."
This same article says that animals harvested for their blood and returned to the water alive are not counted toward the state's quota.
Some crab areas appear to be significantly depleted, while others are rebounding. There is still a market for horseshoe crabs as bait. Anecdotal observation along our stretch of Buzzard's Bay suggests that there are far fewer crabs in our waters than were present in the 1970s. We do not find the washed up shells of their young anymore while beach combing as we used to do. I would need to be out on the beach in early June with the full moon above to be certain, but for a species that is so central to maintaining a healthy coastal marine ecosystem to leave so little trace of itself along our shore today is reason enough for concern.