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.

3 Responses to “Horseshoe Moon”

  1. 1 Rebecca May 24, 2012 at 9:29 pm

    This brings back great memories of seeing them in Georgia, all thought we didn’t have quite as many that far south. I can definitely tell it’s horseshoe crab season when two different blogs I read post about them on the same day! (The other is here –

  1. 1 Molts « Backyard and Beyond Trackback on August 7, 2012 at 7:48 am
  2. 2 Life Along The Delaware Bay | Backyard and Beyond Trackback on May 31, 2013 at 7:17 am

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