Saturday, July 5, 2014

Sex on the beach


At Toms Cove and other sheltered beaches on the Atlantic coast, late spring brings Atlantic horseshoe crabs (Limulus polyphemus) to mate and lay eggs. Jessa jokingly describes this as "monsters making more monsters".




Each female can lay tens of thousands of eggs, many of which are eaten by shorebirds such as these short-billed dowitchers (Limnodromus griseus).

  
Another shorebird, the red knot (Calidris canutus), is so dependent on horseshoe crab eggs that the eastern North American subspecies (C. c. rufa) may become extinct if recent declines in the Limulus population are not reversed. (Causes for the decline are thought to include habitat changes as well as overharvesting for bait and for medical research and testing.)

During their visits to the beach, some of the horseshoe crabs get turned upside-down by the waves, and will perish if they cannot right themselves using the telson or spike-like tail. This is one of several we rescued [Just flip 'em]—an opportunity for a good look at the creature beneath the carapace.


A good many of the horseshoe crabs don't come alone, but bearing hitchhikers. This specimen is covered in limpets; others that we saw carried barnacles.


After their romp on the beach, the horseshoe crabs return to the deeper waters of the continental shelf, leaving only tracks and the bodies of the fallen.


...and, of course, the birds.


[For more information on these fascinating "living fossils", please visit the website of the Ecological Research and Development Group at www.horseshoecrab.org.]

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