Posts Tagged 'horseshoe crab'

Life Along The Delaware Bay


Highlights of past Horseshoe Crab posts
Horseshoe Moon
Horseshoe Crabs


First Horseshoe?










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.


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