Ask the Aquarium - Fiddler crabs help keep saltwater marshes healthy

Q. We saw a bunch of baby crabs in the mud along the sound. They were brown and ran off as we approached. What were they?

A. These busy little crustaceans are fiddler crabs and are easily spotted at low tide along marsh shorelines. Three types of fiddlers live along North Carolina’s soundside marshes; the sand fiddler, mud fiddler and marsh fiddler. Depending on the type, the small crabs seldom reach more than 1 to 1½ inches in width.

Male fiddlers are easily identified by their enormously enlarged singular claw, which they wave almost constantly.

Female fiddlers are equipped with two small claws. Some say the male’s waving resembles a musician playing a bass fiddle. Others say it reminds them of a conductor leading a symphony. The gesture is actually to defend territory and attract mates.

To deal with the rise and fall of tides and to escape predators, fiddlers live in burrows a foot or two deep in the sand or mud. Stacks of pellets near the dime-size openings are from their excavations. It’s believed the burrows help ventilate the mud and help keep the marsh healthy.

The crabs feed during falling and low tide. When the water begins to rise they slip into their burrows and place a mud plug in the opening. In winter, they disappear into their burrows for a sort of hibernation and pop out again with the arrival of warm weather.

Fiddler crabs are almost exclusively plant eaters, feeding mainly on bacteria, minute algae and decaying plant matter they pick out of the mud. They are preyed upon by raccoons, terrapins, fish and birds.

This information was provided by the North Carolina Aquarium at Pine Knoll Shores. The state operates three public aquariums; Pine Knoll Shores, Fort Fisher and Roanoke Island. The aquariums are administered by the N.C. Department of Environment and Natural Resources and are designed to inspire appreciation and conservation of North Carolina’s aquatic environment.

For more information, visit www.ncaquariums.com or call 800-832-FISH.