Horseshoe crabs will win no beauty contests. In fact, they look menacing enough to young Eden Gass, it took her most of the evening Saturday to work up the nerve to touch one, as you will see in the photo gallery included in this post.
But despite appearances, horseshoe crabs don’t bite, sting or pinch.
And they could use a little help from humans once in a while.
That is why Eden and more than 30 volunteers showed up Saturday at Harbor Island’s beach. They learned about horseshoe crabs, then helped gather males from the surf so they could be tagged.
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As Eden and the other participants learned, there’s at least one other time you should lay hands on horseshoe crabs. If you come upon one on the beach flailing on its back — a common sight on Lowcountry beaches this time of year — set them upright again. Doing so keeps them from baking out or getting their gills pecked out by sea gulls.
Indeed, these critters are worth having around.
If you’ve ever had an artificial joint implanted, been inoculated or undergone any sort of invasive surgery, you’re almost certain to have benefited from the horseshoe crab’s existence. That’s because their blood is used to ensure needles, vaccines and surgical instruments are sterile.
Their copper-based blood is blue and contains amebocytes, which play a role similar to the white blood cells of vertebrates in defending against pathogens. As such, their blood can be used to detect bacterial endotoxins. Licensed collectors — of which there are only three in South Carolina, according to S.C. Department of Natural Resources veterinarian Al Seagars — take crabs to a lab in Charleston, where their blood is drawn for processing. Amebocytes are separated from the blood and used to test intravenous fluids and items such as artificial joints and surgical instruments.
The crabs are then returned to salt water of the same salinity from whence they came.
Seagars spent about 45 minutes Saturday explaining the many wonders of horseshoe crabs to the volunteers, who were participating as part of DNR’s Coastal Exploration Series. (Incidentally, the turnout was far larger than for any of the other previous events, Seagars said.)
The event was timed to coincide with the full moon, which calls ashore female horseshoe crabs to lay their eggs and males to fertilize them. (Coincidentally, this past Saturday’s full moon was the first of three summer “supermoons,”, which brings the satellite close to Earth and causes unusually high tides.)
Harbor Island in northern Beaufort County is an active breeding ground and a place where DNR frequently tags the crabs to help scientists learn more about the their migration and habits. As fast as volunteers could scoop them from the water, Seagars drilled a small hole in their shells and inserted small, round tags.
Volunteers were taught to distinguish males from females and instructed to collect only the males for tagging, so that the females could be left to their important chores. It takes about eight years for a horseshoe crab to reach sexual maturity — surprisingly late for an invertebrate — and only a handful of the tens of thousands of eggs a female will lay in a season are likely to produce a crab that survives long enough to make it back into the water.
The local tagging project, part of a federal Fish and Wildlife Service program, began in 2007 and is now performed on Daufuskie, Hilton Head and Edisto islands, as well, according to John Albert of Harbor Island.
Albert was Harbor Island’s liaison for the DNR event, and, as a member of the Fripp Island Audubon Club, he has an additional interest in the horseshoe crabs. Their migration is followed by red knots, robin-sized birds that feast on the horseshoe crab eggs to sustain their annual migration of 8,000 to 10,000 miles, from the tip of Argentina to the Arctic.
The red knot is amazing in its own right. It has one of the longest migrations of any bird, according to the Cornell Lab of Ornithology's Web site, All About Birds. As they prepare to fly, they gorge on mussels. The muscles they use for flight swell, and their stomachs shrink. The birds then begin their migration, flying as long as four days without stopping.
When it finally is time to recharge, they stop along the Eastern Seaboard, timing their arrivals to the ancient mating movements of the horseshoe crab. The red knots need easily digestible, high-protein food, and horseshoe crab eggs, which are barely larger than a grain of sand and laid by the tens of thousands, are perfect, Seagars said.
The tie between the horseshoe crabs and red knots has loosened drastically over the years, as the bird’s favorite food source has dwindled, mostly in northern states where fishermen harvest horseshoe crabs for bait. They split pregnant females in half and put them in traps that are much like crab pots, catching conch and eels, according to Seagars.
For more on the horseshoe crab, read the photo captions in the accompanying photo gallery. You also can watch this video by Coastal Kingdom’s Tony Mills, produced by the Beaufort County Channel and the nonprofit LowCountry Institute.
Weird Creatures show about horseshoe crabs, The Science Channel
Red Knot Shorebirds documentary video by American Road Journal