Two 'ghostly' creatures inhabit Georgia beaches. The 'ghost' most often encountered is a crab. The pale color and nocturnal behavior of these shore crabs make them aptly named. Seen silently scurrying over the sand in the moonlight, they do seem like other-worldly apparitions.
Photo of ghost crab "Ocypode quadrata (Cahuita)" by © Hans Hillewaert. Licensed under CC BY-SA 4.0 via Wikimedia Commons
Ghost crabs are related to marsh fiddler crabs, and like the fiddlers they mainly live on land, excavating deep tunnels in the upper beach and sand dunes. During the day they renovate their burrows or rest in the cool, moist subsurface. After sunset, they emerge to spend the evening scavenging for dead animals and hunting small clams in the surf.
A ghost crab burrow dug in the upper beach on Sapelo Island, with crab tracks and excavated sand balls around the entrance. By E. Sherr
Like other land-dwelling crabs, ghost crabs release their broods into the ocean to live as plankton. The final, megalopa stage of a ghost crab larva has a strong, rounded carapace that protects it from the surge of the waves as it makes its way into its new home on the beach.
The other 'ghostly' animal, although common, is rarely seen. The ghost shrimp is a strange-looking beast, up to four inches long with an elongated abdomen and large, slender front claws. These shrimp live in two- to four-foot-deep burrows in the moist sand of the surf zone, constantly pumping water through their tunnels for food and oxygen.
One branch of sedimentary geology focuses on fossil tracks, burrows, and other imprints of animals in sand and mudstone formations. Geologists study the traces made by living coastal animals as an aid in figuring out who made what fossilized markings.
In a companion blog to his excellent book 'Life Traces of the Georgia Coast,' Dr. Antony Martin, a professor at Emory University in Atlanta, has an informative post about ghost shrimp and their burrows on sea island beaches from a geologist's perspective.
Because they lead a sheltered existence, ghost shrimp exoskeletons are softer and more flexible than the hard shells of water-dwelling shrimp and crabs. The shrimp excavations are narrow at the top, opening up into a roomier living space about an inch across. When runnels on the beach erode away the top few inches of these holes, the larger bottom sections appear as 'chimneys' jutting up from the sand, held intact by their builders' mucus secretions. Other creatures find refuge in the security of ghost shrimp tunnels. A common burrow-mate is a tiny commensal crab, a close relative of the pea crab found in oysters.
Two ghost shrimp burrows surrounded by 'chocolate sprinkle' fecal pellets on Nannygoat Beach, Sapelo Island. By E. Sherr
Ghost shrimp are most evident by the definitely non-spiritual droppings strewn about their burrow holes. The dark shrimp feces are the exact size and shape of chocolate sprinkles. A professor used to shock his students during field trips to Sapelo Island by pretending to scoop up some of the shrimp feces from the sand, and then popping the 'pellets' (really sprinkles) into his mouth with relish.