If you have ever spent time along the edges of tidal marshes during low tide, the waving of claws of fiddler crabs would surely have caught your attention. The males, with their one oversized claw, look comical as they wave them up and down, resembling a fiddle player, after which they are named. Their wave is believed to help them attract a mate. To see dozens or hundreds of these common marsh inhabitants is impressive, especially when they are spooked and dart into their nearby burrows.
Those burrows are excavated in the muds and sands of tidal marshes across the globe, where these crustaceans are important elements of the food chain of estuaries and tidal portions of rivers. There are 13 species of fiddler crabs in the Gulf of Mexico alone, with four found in Mississippi. Their preferred habitat is vegetated marshes and adjacent muddy/sandy flats where their fiddling can be spotted and where they feed during low tides.
Males and females excavate burrows along the edges and open interior portions of marshes. They do not stray far from their burrows, where they seek shelter from predators and where they retreat during high tides. Mating also takes place in burrows. Fiddlers can cap their burrows with mud and sand during high tides and spend winter months there. Their travels away from their burrows are all about finding new patches of mud and sand from which they glean the rich mixture of algae and bacteria that grow across the surface of marshes.
Fiddler crabs feed using unique spoon-shaped bristles on their mouthparts that efficiently separate mud and sand from food. If you are patient enough to watch, you can see them as they repeatedly scoop up sediment with their claws and roll balls of sediment between their mouthparts. Once a ball is sufficiently processed, they spit it out, pivot to the side and repeat, leaving a trail of small “feeding balls” on the surface of the marsh. Males must work harder with their one “feeding” claw. Females can look like they are stuffing their face, as they use both claws. Larger balls of sediment can be found around the mouth of their burrows and represent the sediments removed, dragged out of the burrow with their walking legs – often after every high tide.
As for their role in the food chain, fiddler crabs process the rich and abundant algae and bacteria that are at the base of the food chain and transfer it to a multitude of higher-level components. They are prized food for just about any predator that walks or swims in marshes, from birds, small mammals, fish and other larger crustaceans. A research friend and I documented juvenile fiddlers as being the overwhelming component in the guts of Gulf Killifish after they left the marsh surface on ebbing tides. For those of us that fish for Sheepshead, fiddlers are the very best bait.
Of the four species of fiddlers found in Mississippi, two are most common. The Gulf Marsh Fiddler (Minuca longisignalis) can be extremely abundant in brackish to higher salinity Needlerush and Cordgrass marshes. Males have elongated claws that give this fiddler its species name. Their carapace is often aqua/green in color. My favorite is the larger, Red-Jointed Fiddler (Minuca minax), which sports red spots in the joints of its claws. This species prefers the low salinity tidal regions of coastal rivers and can be found many miles upriver.
Fiddler crabs are an important part of coastal and marine ecosystems and can be fun to watch. Take the time to find them and enjoy the show. You will not be disappointed.
Hope to see you in our great outdoors!