Pat's Wildways: Fiddler Crabs

Low tides are my favorite times to go to the seashore, wherever I am. On the West Coast of the United States, the pools left behind the retreating tides are full of anemones, urchins, sea stars, and all kinds of colorful invertebrates — a wonder to behold.

Here on our coast though, the low tides are not nearly as colorful, but the life there is as vibrant if you just know where to look. Our ocean beaches do have little pools when the tide retreats, but most often, there is nothing left there to see. Yes, there are clams on the beach, or ghost crabs if you are up early to see them, but not much else.

But wow, take a look at the river side of our island at low tide and there’s a world waiting there to discover. One good place to take a look is the Dee Dee Bartels boat ramp at the north end of the island. There are paths on either side of the ramp that take you to the water’s edge, with very different habitats on each side. If you take the north side path, you will come to a sandy beach, where a whale carcass was buried years ago (but that’s another story). At low tide, beyond the beach, there is an expansive oyster bed, mud encrusted with oysters that, at this time, are not certified safe enough for people to eat, what with the years of effluents streaming into our waters. It’s a barren-looking land of oysters and mud, but it does attract fishermen who wade out to try to catch the flounder and other fish that come in to feast at the submerged edge of the oyster bed.

The real action, though, is on the other side of the boat ramp at low tide. A few days ago, I wandered down this path south of the ramp and found a whole village of fiddler crabs in full mating mode. Near the water’s edge, there was a large expanse of mud pockmarked with holes and covered with piles of small mud balls, a sure sign of fiddler crabs. As I moved closer, the crabs scurried out of sight into their holes, but when I stayed still for a bit, the whole scene came to life.

Male fiddler crabs with their one large claw came out of their holes to raise their claws and to vibrate them quickly — a signal to show off their prowess to prospective less-conspicuous females that moved around the mud, sizing up their choices. When a male sees a female, he ups his game and soon tries to lure the female into his hole. An interested female may join him in his hole. If she resurfaces quickly, the match was not a success. But if she stays in a while, before too long, she will be carrying a trove of thousands of small eggs that will hatch in the water in a couple of weeks to establish a new generation.

This observation got me interested in fiddler crabs once again. I visited the two bait stores in Fernandina Beach to learn some more. As fishermen know, hermit crabs are a great bait for sheepshead and other coastal fishes. Both stores had large concrete bins full of hermit crabs that, without holes to hide in, herd to the far corners in a heap to hide under one another. This group herding behavior turns out to be a great way to catch them. Bait fishermen sometimes sink a container in the mud, a pit trap, and herd roaming crabs into it. I can’t see this technique working when crabs are actively breeding and individually attached to their retreat hole, like I saw at the boat ramp. But elsewhere and at different times in their lives, some fiddler crabs go on mass migrations. And then, if a pit trap is in their way, too bad. They could end up at a bait store and then on the end of a hook.

Fiddler crabs are by no means endangered, and there are a handful of species found in our own coastal areas. They form a useful service in our marshes, filtering small bits from the mud to feed on, leaving discarded mud balls behind. Lots of animals, from fish to birds, eat fiddler crabs — they are a key part of healthy tidal ecosystems.

And they are lots of fun to watch. Next time it is a low tide, take a look at the crab colony beside the boat ramp. If you are like me, you may spend long minutes just watching a single male crab in his efforts to best his peers and lure the females into his lair. Sound familiar? Check it out!

Pat Foster-Turley, Ph.D., is a zoologist on Amelia Island. She welcomes your nature questions and observations. patandbucko@yahoo.com