If you walk down the beach on Cumberland Island you will eventually come upon the shell of a horseshoe crab.  Sometimes visitors encounter large numbers of these ancient animals beached along the shore.  Horseshoe crabs which are more closely related to spiders than crabs have been around for over 400 million years according to fossil records, and have not changed much in form over the last 200 million years.  They are true survivors that have made the right biological adaptations to face their environment.  Along with a total body covering shell they have a protective copper base blood that allows them to live on the bottom of the surrounding shallow seas where there are heavy concentrations of bacteria.  Because they are such a unique animal they have become the focus of a lot of research and several medical uses have been found for their blood.

  But horseshoe crab populations have been impacted along the east coast for a number of reasons.  In come cases, they have been used heavily for bait in blue crab traps.  However nothing is isolated in nature so there are other animals that depend on them.  Shore birds in particular rely on horseshoe crab eggs for a food source.  Some species like dunlins and red knots time their migrations around the spawning of these crabs in the mid-Atlantic states.  during this period large numbers of mating pairs come ashore at the waters edge to deposit and fertilize their eggs.  On Cumberland Island however the mating activity is much more sporadic.  The horseshoe crabs found on the beach are more likely to be individuals washed up by storms or simply animals that moved onto the beach at high tide and were stranded as the tide receded.  Horseshoe crabs also molt, so the old shells they discard come ashore as well.  After molting, a horseshoe crab can be twenty-five percent larger than it was before.

One interesting note:  I have found some biologists reluctant to refer to horseshoe crabs as primitive animals.  This is due to the fact that they have made few if any evolutionary changes over the course of millions of years.  On the other hand, relative new comers such as mammals including humans are still evolving.  But unlike other animals, humans can rapidly alter the environment.  Time will tell if both humans and horseshoe crabs will be able to keep up with the rate of these changes.