Posts Tagged 'horseshoe crab'

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.

Limulus Polyphemus

For my birthday, I was given the gift of a tattoo. The work was done by Robert Bonhomme when he was still at Brooklyn Tattoo. Robert told me that when he was a kid, his siblings would run around local beaches searching for shells, while he was always on the lookout for horseshoe crabs. That sounds like August on the East Coast to me; the shed exoskeletons of these animals, complete in every detail, are to be found up and down the seaboard then.

I’ve written about horseshoe crabs and how they may have saved your life because of LAL (limulus amebocyte lysate), the substance extracted from them and used to test medical equipment, and how we’ve scandalously allowed their numbers to dwindle precipitously through over-fishing (they are chopped up for bait) and other sins.

I may be a little bit obsessed by them, an utterly fascinating life form, key to a whole littoral foodweb and vital to human health, but I’m not the only one, since “Horseshoe Crab” is consistently one of the main search terms that finds this blog. As an example of the Horseshoe’s ecological importance, its decline is directly linked to a rapid decline in Red Knot (Calidris canutus) numbers; the U.S. subspecies of this long-distance migratory shorebird depended on the formerly bounteous production of Horseshoe Crab eggs in the Delaware Bay.

Horseshoe Crabs

I wrote about the Atlantic horseshoe crab, Limulus polyphemus last week, before I got a chance to head out to the city shore to look for some this year. So that was theory, this is practice, at Plumb Beach.
And practice can be hands-on. If you should happen to see a horseshoe crab wrong-side up and obviously still kicking, be a good sport and turn it over. They are absolutely harmless to you, so don’t be afraid of them. Don’t use the telson, or tail, however, which is very delicate and easily damaged (it’s got sensors to tell day from night); just use two hands on the outer edge of the main part of the shell (the helmet-like prosoma) and turn it over.

Note the slipper shells, Crepidula fornicata, hitching a ride.

And on top, barnacles as well as slipper shells. Another of the crabs had a cluster of blue mussels growing on it. Plowing through the sand of the littoral, and further out at sea, the tank-like bodies are home to many other species.
That’s the mouth right there in the center. This is a female, since it’s lacking the modified pedipalps/hooks that the male has instead of a first pair of walking legs.
That’s the smaller male on the back attempting to do his ancient duty. He grabs on with his pedipalps.
You may want to open this image up for a better view. I think that’s a horseshoe crab nest there in the upper middle of the image. After laying her eggs, the crab then looped the loop on the lower right, and headed back to the sea.

Limulus Polyphemus

Spring, the new moon: The littoral of the city is filling with mating Atlantic horseshoe crabs. The males of Limulus polyphemus, sometimes several at a time, are clamoring aboard the larger females, who come ashore at high tide to lay their eggs at the wrack line. A female may lay 90,000 eggs in a season. Many of these eggs are eaten by a least two dozen species of hungry shorebirds; the red knot in particular depends on them on its long migration from the South Atlantic to arctic Canada.
The three main parts of the body are the telson, or tail; the opisthosoma, or abdomen; and the prosoma, or cephalothorax. Horseshoes have numerous optical sensors, including compound eyes, median eyes, ventral eyes, and photoreceptors on the telson to tell the time of day. Their species name comes from the Cyclops blinded by Odysseus, because of the central eye on the forehead of the prosoma. Additionally, an astonishing 7 million neural fibers allow the animal to feel and sense its world.

This is a shed shell of a young horseshoe. You can tell because of the tan color and the fact that it’s hollow inside; every little jointed part is empty now. To grow they must molt: males may molt 16 times over nine years, females 17 times over 11 years, before reaching sexual maturity.

Now here’s the stunner: You may owe your life, or the life of a loved one, to the horseshoe crabs and not even know it. Even if this extreme isn’t part of your personal experience, you still have horseshoes to thank for the safety of intravenous drugs, vaccines, and medical devices, because for 40 years a substance extracted and refined from the blue blood of horseshoes, called Limulus amebocyte lysate (LAL), has been used to test medical equipment for bacterial contamination. You see, sterilization isn’t good enough when it comes to bacteria; the bacteria may die, but components of it, called endotoxins, can survive, and that’s grim news for you and I. But horseshoes live in the littoral, which turns out to be awash in microbial trouble. They don’t have immune systems as we would think of them, but they need a defense against potentially harmful bacteria, viruses, and fungi hanging out in the goo. Their blood clots around these potentially deadly forms, deactivating them and helping to seal wounds. An elegant solution in the sea.

So scientists at the Woods Hole, MA, Marine Biological Lab figured out that LAL would make a great test for endotoxin. It replaced the rabbit test. To this day, horseshoes are bled up and down the coast for this purpose. Most survive the procedure (studies show a range of mortality: the industry says 3%; non industry sources say 10-15%), but if ever a synthetic were necessary, it would be here.

And for this noble work, shamefully unnoticed by most, how have we treated the horseshoe crab? Why, with typical human consideration, of course: there’s the usual befouling and destruction of habitat, which escalates up a complex chain of animals species who depend on horseshoes for food and shelter (the shell can be festooned with dozens of species). And there’s the wholesale slaughter of millions of horseshoes for bait by the conch (whelk) and eel fisheries. Yes, they are chopped into chum. How fucking obscene. At least they aren’t ground into fertilizer anymore.

In our childlike, vain, and preening view of the world, horseshoe crabs –- more related to spiders and mites than crabs — are considered “primitive” life forms, low down on the “tree of life.” The notion of a tree of life seems to me to have been one of the compensations of the shocking post-Darwinian world, when many humans still had to feel that we were top animal, that evolution led higher and higher to us, up there in the high branches, waving our thumby paws with smug satisfaction. What vanity, to dethrone a god and put ourselves in its place!

One day we too will be extinct, like the great majority of all life forms that have existed on this planet. And unlike all the others, we will have been responsible for the destruction of great numbers of our own and many other whole species. It behooves us to consider the horseshoe crab, polyphemus scuttling across the seas for 20 million years, its relatives for 200 million, perfectly suited to its life, amazing and beautiful, and learn a little humility. Should we not use our fatty brains, our vaunted consciousness, and our handy tools in service to the planet instead of towards its dismemberment? Why is this even a question?

(Leap into the future for a another post about horseshoes in action.)


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