Spring Full Moons, Horseshoe Crabs, and Migratory birds

Talented Island Photographer Bubber McAlhany sent this photo today, of two crabs embedded in sand.

During the week this week, there was a full moon, with high tide falling right at dusk. The full moons in April, May, and June are spawning times for Horseshoe crabs, Limulus polyphemus. For millenia, these prehistoric arachnids have been coming ashore to lay eggs on a full moon tide. The eggs are buried in the sand, and within them, the crab molts 4-5 times in the next two weeks. Two weeks later, the new moon again creates an above average tide, and the tiny crabs hatch out and take residence in the sea. Turtle watchers and beachcombers are encouraged to interfere with crabs that appear stranded ONLY if they are flipped upside down. (The information campaign encourages you to “just flip ’em,” turning them over and pointing them to the sea.) If, for some reason, they do not have a telsun (tail) strong enough to flip themselves over, you can help them out.

If you look up some evening and the moon is full, think about an ancient creature stirring on the ocean floor or a small bird flying through the night.  (PBS special, A Tale of Two Species)

Horseshoe crabs provide slow moving real estate for other organisms, like this slipper limpet.
Horseshoe crabs provide slow moving real estate for other organisms, like this slipper limpet.

Horseshoe crab eggs are a really important source of food for some migratory predators, like the red knot, a tiny shorebird that winters in Chile and nests in the arctic. Birds time their stopover resting in places where horseshoe crabs are spawning. (We saw a few red knots in Copahee sound over mother’s day weekend, and you can see ruddy turnstones flipping over the sand in search of eggs on many area beaches.) My Master Naturalist class took a trip to the ACE basin last week, and found out that there is a migrating population of red knots that has been banded there, who were NOT recaptured in Delaware Bay. This would mean that rather than hopscotching their way up the coast, red knots fly thousands of miles with very few stopovers. Which makes the time they spend here and in the ACE Basin even more important to the survival of the species.

Here is a link to a very interesting video on PBS
about red knots and horseshoe crabs… from the way we harvest and test horseshoe crab blood right here in Charleston, to the people who tag red knots on their journey, to the massive impact each species has on the survival of the other, it is a comprehensive look at a whole ecosystem. I enjoyed the video, and highly recommend it.

Here’s a link to a post about Horseshoe crabs and a lecture by intern Erica a few years back.

This Post Has One Comment

  1. judydrewfairchild

    I am adding Bubber McAlhany’s gorgeous photo of two crabs embedded in sand, which he sent me this morning!

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