Posts Tagged 'horseshoe crab'

Along the Shore


Life Along The Delaware Bay

I didn’t make it to the beach to witness the annual rites of spring of the Horseshoe Crabs (Limulus polyphemus). But I did manage a virtual trip with this beautiful book. Life Along The Delaware: Cape May, Gateway to a Million Shorebirds by Niles, Burger, and Dey, with photography by van de Kam, was published by Rutgers University Press last year. It’s a coffee table book with luscious photographs, but also one with a scientific bent. Indeed, even a point. The Bay is one of the most important ecosystems on the East Coast, but isn’t nearly as well-known as the Chesapeake. It’s especially important for shorebirds in migration, those epic flights to and from breeding grounds in Arctic Canada. For at least since the last ice age, this migration has coincided with the annual Horseshoe Crab breeding season. Massive amounts of Horseshoe eggs fed these long distance migrants, providing a vital half-way point. After more than a century of slaughtering Horseshoes for fertilizer, bait, and medicine, there are now many less Horseshoe crabs. Hence, less birds. A subspecies of Red Knot (Calidris canutus) in particular has been hard hit. These birds are known to fly six days straight (songbirds migrate during the evenings only, resting and eating during the day); indeed, before starting from Patagonia, Red Knots shrink their digestive systems to lessen their weight (mirroring the ability of birds to shrink their gonads once breeding season is over). The easily digested, protein-rich Horseshoe eggs are vital to the survival of the Red Knots. This is the main story told in this book, but it’s not the only one. It’s thoughtful, up-to-date, and, as noted, extremely well-illustrated.

Highlights of past Horseshoe Crab posts
Horseshoe Moon
Horseshoe Crabs

Two punks from Bergen Beach were recently busted for poaching horseshoes from Jamaica Bay. Telsons should to driven into their gonads. They were caught pretty much by accident, by NYPD detectives testing night-vision gear in a helicopter. Park Police have a boat, but it remains tied to the dock.

First Horseshoe?

We approach the first anniversary of my now constant companion, the distinguishing identifiable feature of my corpus, my horseshoe crab tattoo. So I was most pleased to notice this detail in the book, Natural Histories, I reviewed in my last post. In 1590, Theodor de Bry’s opus America presented some of the first images of the New World to the Old. Bry (1528-1598) and his sons made engravings from the paintings of John White (c. 1540-1593), who was appointed Governor of Roanoke Colony in 1587. One of these shows some of the original (native) Americans in a canoe, and in the lower right corner, a couple of the underwater creatures encountered along the Virginia shore.

Is this the first published European representation of the Atlantic Horseshoe Crab (Limulus polyphemus)? It’s almost right. The tripartite body is well-rendered, but the legs are wrong, since they don’t actually extend from underneath the animal. It’s as if White and company crossed a Horseshoe with an actual crab. Though called “crabs,” Horseshoes are not members of the Crustacea.

One of the recorded Native American names for the Horseshoe is Se-ekanau or Seekanau. In English, it has been called the horsefoot crab, saucepan crab, soldier crab, king crab, and helmet crab. “Horsefoot crab” was coined by the British naturalist Thomas Harriot (c.1560-1621), who puttered around the New World (specifically that region that we’d now call the Carolinas and Virginia) in 1585 with Sir Walter Raleigh (c. 1554-1618) and thought the supposed crabs looked like horses’ feet. This is the source, via language’s slippery slope, of our name “horseshoe.” Meanwhile, the words in the binomial name actually do mean something. Limulus means a little askew, referring to the placement of the animal’s compound eyes. Polyphemus is the name of the one-eyed Cyclopes gorily blinded by Odysseus. (The much-studied and many-martyred Horseshoes have an impressive array of eyes and and other light-sensing organs and were instrumental in discoveries about vision, including human vision.)

Francis Parkman (1823-1893) wrote of Samuel de Champlain (1574-1635), who explored as far south as Cape Cod in 1604-1605: “The ‘horse-foot crab’ seems to have awakened his special curiosity, and he describes it with amusing exactness.”

A delightful show on wunderkammer at the Grolier Club revealed another of our old friends in the frontispiece illustration of Ole Worm’s Museum Wormianum, 1655, a catalogue of “one of the great attractions of 17th century Copenhagen.” ole worm


You should be seeing the shed exoskeleton’s of Atlantic Horseshoe Crabs on our beaches now. Note how they are hollow right down to the smallest joint.

As arthropods, Horseshoes must molt to grow larger: they do it about half a dozen times during their first year and then some 18 more times after that before reaching sexual maturity, at around 9 (males) – 12 (females) years of age. July and August are the big molting months.

The pewter pin in the picture showed up in the mail after I reported a tagged Horseshoe at Plum Beach in May.

Sheepshead Bay

Ten piers, ten local creatures of the sea.


A Great Black-backed Gull scavenges a Horseshoe crab.

This is the last full moon of the Horseshoe spawning season. Gravid females can lay tens of thousands of eggs during the season, making successive trips to shallowly bury their eggs at the high tide line. Very few of those eggs become adults. I’ve seen one estimate that says only 10 individuals will reach adulthood out of tens of thousands of eggs. Once, where there were millions of Horseshoes up and down the east coast, all these eggs were key to an littoral foodweb, with migratory birds and ocean animals scarfing up the rich bounty of protein. But enough Horseshoes made it to spawning age — it takes 9-12 years — so that, with the usual highs and lows of natural cycles, it all evened out in the long run. And Horseshoe crabs have had a long run; their ancestors go back some 400 million years — that predates the dinosaurs by some 200 million years.

No more: Horseshoe populations are plummeting. Long Island sees less and less of them every year. Why? They were ground up for fertilizer by the ton until the mid-20th century. Right around the time that assault finally stopped, they started being chopped up for bait for the eel and whelk fisheries. Combined with beachfront development, poisons (a.k.a. pollution, the costs fobbed off by corporations onto the world’s biotic, including human, communities), and such assaults on the ocean as dead zones, warming, and acidification, the Horseshoe population has taken a big hit.

Meanwhile, and here’s what really gets me, they’re also bled for our benefit. Anyone who’s ever taken antibiotics, much less had surgery or prosthetics — owes something to Horseshoe crab blood, from which the bacteria-detecting LAL is extracted and used world-wide to test pharmaceuticals and medical devices. (The industry says 3% of these bled Horseshoes die; others say it’s more like 10-15%.) Personally, I think we owe these animals a lot more thanks than the hacking of them into pieces of bait for eel and whelk eaters.

Horseshoe crabs were also instrumental in advances in the science of vision — who’d a-thunk it? — and the understanding of chitin (which is now found in everything from tampons to livestock feed, although it’s not commercially derived from Horseshoes).

Some of you may, in a way, owe your life to this animal, whose ancestors survived two global extinction events but may not get through the present one.

I usually see my Horseshoe crabs at beaches that are part of Gateway National Recreation Area. You can’t harvest Horseshoes there, so I kinda always assumed that it would be the same elsewhere in the state. Wrong! Gateway’s federal. New York shamefully allows licensed commercial exploitation. Additionally, individuals can take a max of five a day in season for “recreational” purposes w/o a license.

UPDATE: Through the magic of the internets, I’m actually not on the long island whose western-most end is Brooklyn at the moment. I’m at the far eastern end of the terminal moraine/outwash plain, on Nantucket, and today I spotted two Red Knots, the increasingly rarer shore bird that migrates up from South America to the Canadian arctic, a bird heavily dependent on Horseshoe crab eggs. I’ve never seen them before.

Horseshoe Moon

Can you feel it? The Horseshoe crabs (Limulus polyphemus) sure can. It’s spawning season. Here, looking like rocks, are some males awaiting females and clusters of males attached to, and surrounding, females.

Could it be their multiple optical systems, including compound eyes and UV sensors? Could it be their one hundred thousand cuticular receptors, allowing them to feel their way along? Or the chemosensory pores that connect their dendrites to the water? Whatever it is, they can smell the pheromones…A huddle of males around female mostly-buried in the sand under the clump of seaweed. Horseshoes started their evolutionary journey something like 450 million years ago. They predate the dinosaurs, and, needless to say, the species that chops them into bait, grinds them into fertilizer and chicken feed, and sucks their blood for human medicine. There are four species, three in the Indo-Pacific (where they are also eaten by H. sapiens), one in the Atlantic. Related to the trilobites and the arachnids, they are not crabs; they survived the Permian-Triassic Extinction that killed off nearly all other ocean life. It is fashionable to call them “living fossils,” but that suggests a simplicity that the reality belies. The full and new moons of May and June bring them in-shore to mate and lay their eggs in the sand at the high tide line up and down the east coast. NYC is no exception. Jamaica Bay has been prime nesting habitat since the retreat of the ice.
Not all of them return to the sea. There are more than a dozen dead in this photo. Legion are the hazards of being a Horseshoe crab.Between the devil (you will know him by his works) and the deep blue sea, there are a lot fewer Horseshoes than there used to be, a situation which has ramified throughout littoral habitats and their food chains. As a result, the animals are much studied, with censuses conducted up and down the coast this time of year. This tag, one of five we saw among the several hundred crabs about an hour before high tide, had only been attached two nights earlier by a team from NYC Audubon.
Pointing out some anatomy on the underside, where the appendages, including the chelicerae, and book gills make for a fascinating contrast to the helmet-like topside. Note blade of Spartina in hat band… but that’s a whole other story. Thanks to Traci for the photo.


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