By Alex Scott
Stone crabs found by Ann Fisk
At first glance, a casual visitor to Satellite Beach in Brevard County, Florida, may mistake these hunks of gray rock for another washed up pebble. Others may confuse them for the mystical rock crabs from the Pirates of the Caribbean movies. But the real answer is: they’re a little bit of both!
Atlantic ghost crab (Ocypode quadrata) by Lynn Wilkes
Neither a plain pebble nor a magical being, these amazing finds are actually 110,000-year-old ghost crabs that have been perfectly encased in coquina rock. The Atlantic ghost crab, or Ocypode quadrata, is an animal that looks much like any other member of the crab family, with its one large front claw and hard carapace. Coquina rock is a sediment made of ground-up shells that have been deposited onto the shore, and is found along the world’s coastlines. But despite the widespread distribution of the ghost crab family and coquina rock, these “stone crabs” have only been discovered on the beaches of Brevard County, making them a particular delight for scientists and beachcombers alike.
A 2003 scientific article published in the Journal of Crustacean Biology documented this phenomenon by studying over 500 of these stone crabs. The article posits that the unique conditions of the coastline in this area, including tidal patterns, prevalence of storms, sediment from nearby Cape Canaveral, and the coquina rock from the mineral deposit that the researchers have named Anastasia Formation, all worked together to create the perfect stone coverings around the crabs.
Stone crabs found by Barbara Smith, Atlantic ghost crab burying itself in the sand by lunarr.photog, stone crab found by Brenda Spletter.
The crabs’ neutral sitting positions, with claws tucked under their bodies, suggest that the crabs died in their shelters from cold temperatures, and were preserved right in their hiding places. They remained buried in the Anastasia Formation for millennia until rising sea levels and human interference exposed them to the surface for lucky beachcombers to find.
Three stone crabs found by Bernadette Skipper, stone crab next to the hole of a living creature found by Ann Fisk, stone crab and shell and sea glass collection by Alice Borough Ahrens.
However, even sitting on the beach, these stone crabs are understandably hard to find. Some specimens, like those pictured, are clearly crab-shaped, while others are almost indistinguishable from regular rocks. It therefore takes a trained eye to differentiate the entombed animals from other coquina rocks. But for those who collect them, they are an incredible paleontological find worth the search.
This article appeared in the Beachcombing Magazine November/December 2019 issue.