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A Ghost That Haunts Atlantic Beaches

January 31, 2020

Should you venture out at night on a coastal beach, from Block Island to Florida, you might be greeted by a GHOST, a 2-inch wide critter with periscope-like eyes that can swivel 3600.The sideways-running creature, a ghost crab, sprints tippy-toe across the sand with its two white claws held to either side of its shell.
Stopping abruptly in the beam of a flashlight, the tiny crustacean often freezes in place until covered again by the dark. It then darts off, back to its nearby burrow or parts unknown where it might create a shallow refuge, covering itself in the sand. The only evidence of its presence can be just a pair of black-tip eye stalks rising above the temporary sand-refuge.
When approached by a human intruder, some adult crabs raise their claws and are then known to attack a stick or even a shoe – hopefully not one with open toes! Such action, however, is exceedingly rare.
Ghost crabs are closely related to fiddler crabs, common residents of our coastal salt marshes. In daylight at low tide, fiddlers scurry about in large groups across the mud flats. Ghost crabs however live on the sandy beaches. They are usually loners, emerging from their burrows, usually only at night. Older, mature ghost crabs frequently dig their burrow on a sandy beach, well beyond the high tide mark. It can be up to 4-feet deep with a small chamber at the bottom. To avoid predators and the heat of the day, they frequently plug the entrance to their home and remain there until nightfall. During the early morning hours, the skittish crustaceans can be seen repairing or excavating another burrow. As sand is carried out to the surface, it is spread out around the opening in a fan-like shape.
Younger crabs usually build their burrows in wet sand, near or even slightly below the water’s edge. In daylight, they remain in their burrows even when it is covered with water. During the cold of winter, both the young and the adults remain in their underground hideaway.
Similar to fiddler crabs, ghost crabs communicate with others of their kind by rapping their claw on the ground. They also produce a rasping noise by rubbing their legs together, and a bubbling sound which is believed to be produced within their gills. The males are assumed to create sounds to attract a mate and ward-off male competitors.  The struggle for a female also can begin with two competing males raising their claws and charging toward each other. If the competitor doesn’t back off, the pair may push one another across the beach until one finally relents.
Mating can occur almost anytime during the year. The female carries her developing eggs (=in berry) on her underside. While egg-bearing, she spends most of her time in the safety of a burrow. On occasion, however, she makes her way at night to the surf, to moisten her brooding embryos. As her eggs approach hatching, she returns to the surf line to release them in the water. Carried by the currents for about 60 days, her larvae pass through several stages until the new generation returns to the beaches.
Adult ghost crabs head to the shoreline to feed at night. They consume bits of seaweed washed up on the beach, dead fish and other edible debris. However, it is estimated that up 90 percent of their live prey consists of the ½ inch coquina clam and/or the egg-shaped mole crab. Barely an inch or two long, mole crabs back themselves into the sand, facing the breaking waves. They then extend their long antennae to filter out food particles. When a ghost crab locates and captures a mole crab, it immediately devours the prize or using its claws carries it back to its burrow for later consumption. The chief predators of ghost crabs include raccoons, gulls, and other shorebirds.
Globally, ghost crabs are widely used as indicators of beach health. Their population can be impacted by vehicle and pedestrian trampling. Even necessary beach nourishment, following storm-related erosion, can create a decline in their numbers. It is also true for oil spills and other pollutants. These same factors can severely impact their food supply.
But for most of us, they are simply very fascinating. Begin a search after dark for these ghostly, swift-footed creatures. Armed with a flashlight, head for a more remote or less used portion of a sandy beach. Then walk slowly near the high tide line. The discovery of a ghost crab can be equally rewarding for adults and children. Happy hunting!

 

 

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