Summer photos 8: a horseshoe crab

Sunrise in the field on a flat calm spring tide.

A horseshoe crab, Limulus polyphemus, surrounded by many many mud snails.

Well, this is it, the last week before school starts. And then I will be in the awful part of the year where I am juggling lab, field, and school responsibilities. Before that happens, I went out in the field to collect more snails. It was a beautiful morning, and I was there just as the sun was breaking over the horizon. It was a dead-calm day, as you can see in the first photo up there.

Among the many interesting things that I saw was this female horseshoe crab (Limulus polyphemus). These guys are really amazing. They are not really crabs (not crustaceans), but are more closely related to arachnids. They have remained morphologically the same for hundreds of millions of years, and are different than anything else I have seen on the shore. There's just one species in this part of the world, and I'd never seen it before moving to where I am now. But here they are all over, and I have collected molts of all sizes. One of the coolest sights on the beaches here is in May/June during the spring tides, when they come up onto the beaches by the hundreds to mate. I often barely miss stepping on them as I am walking around in the intertidal. This female got caught high on the shore at low tide, so she dug herself in to stay damp until the water comes back in.

Horseshoe crab blood has many different medical uses, and their eggs are eaten by many species of migrating shorebirds on the east coast of the U.S. Unfortunately, due to heavy use of the species as bait and to habitat destruction, their numbers have been declining for decades.

A deceased horseshoe crab with C. fornicata and C. plana attached. The size of the C. fornicata indicate that they were probably growing there while the crab was still alive, impeding respiration and locomotion. Photo by J. Browne.

They're also very cool because of how different they are from any other group that we study in invertebrate zoology. One of the things that I will miss when I leave this area is seeing them in large numbers, often with their carapaces bedazzled with Crepidula shells.