2014-08-28 / Nature

Fiddler Crab Explosion Indicates Healthy Marsh

By Jack Kelly


Save The Bay interns Grace DeCost, left, and Amanda Adams dig out drainage channels at Gooseneck Cove salt marshes. Save The Bay interns Grace DeCost, left, and Amanda Adams dig out drainage channels at Gooseneck Cove salt marshes. The Gooseneck Cove restoration project, begun nearly six years ago, is a continuing work in progress. As the health and water quality of these vital wetlands improve new discoveries are made on an almost daily basis. Numerous bird, mammal, amphibian and marine species have returned to this once dying marsh system and have helped in its revitalization. Improvements in tidal flows and marsh plant conservation have brought the return of important marsh grasses and formed new mudflats and habitats for wildlife.

Save The Bay coastal ecologist Dr. Marcie Cole-Ekberg, along with interns Amanda Adams, Grace De- Cost, and Emma Rooks, recently traveled to the marsh to assess the conditions of important drainage channels and ditches. The interns are college juniors studying biology and environmental sciences and will put the lessons learned this summer into future projects.


Fiddler crabs emerge from burrows to feed on mudflats across Gooseneck Cove salt marshes. The males' bone-white, oversized claw is visible, and a few are engaged in calling signals. (Photos by Jack Kelly) Fiddler crabs emerge from burrows to feed on mudflats across Gooseneck Cove salt marshes. The males' bone-white, oversized claw is visible, and a few are engaged in calling signals. (Photos by Jack Kelly) The east side of the lower wetlands features two prominent island peat mounds that are the last remaining natural features of this once expansive marsh grass system. Channels were hand-dug into the peat mounds in years past to allow for proper drainage at low tide and to stem the cycle of marsh plant die-off and the resulting toxic algae blooms. A summer maintenance program requires that the channels be cleared of mud and storm debris during low tide, in preparation for the winter months.

The wetlands were alive with wading birds, shorebirds, ducks and raptors as Cole-Ekberg and her party set about their work. Wading to the peat mounds, the group began to clear the channels by hand as they brushed away black flies, mosquitoes and gnats. A Great Blue Heron and a Great Egret, flushed by the human approach, voiced disapproving “gronks” as they took to the skies. A territorial Green Heron fled into deeper foliage.


The immature Bald Eagle that took up a two week residence at Gooseneck Cove, seems to have departed the region. Recently, it had to defend itself against an agressive, territorial Osprey and was forced to flash its talons in response. Both species eat fish and will harass other wraptors that infringe on fishing grounds. (Photo by Bob Weaver) The immature Bald Eagle that took up a two week residence at Gooseneck Cove, seems to have departed the region. Recently, it had to defend itself against an agressive, territorial Osprey and was forced to flash its talons in response. Both species eat fish and will harass other wraptors that infringe on fishing grounds. (Photo by Bob Weaver) As the tidal waters continued to flow out, exposing the banks below the tidal line, an eerie occurrence began to develop. Thousands of Atlantic marsh fiddler crabs began to emerge from watertight bur- rows and scurry to the mudflats to forage for food. While this semiterrestrial marine species is known to occupy the marsh, the sheer numbers present were staggering. “There has been an explosion in crab populations in salt marshes across the state this summer. We are trying to understand and find a cause for the rapid growth rates, but as yet we haven’t found a conclusive answer. We do believe it is an effect of climate change and warmer waters, but the study is not complete,” Cole-Ekberg stated.


Jack Kelly, a native Newporter, is a wildlife photographer and nature enthusiast who enjoys sharing his experiences with others. Jack Kelly, a native Newporter, is a wildlife photographer and nature enthusiast who enjoys sharing his experiences with others. The Atlantic marsh fiddler crab is one of 100 fiddler crab species worldwide. Sizes vary, but the average marsh fiddler is about 1.5 to 2 inches across. The males are easily recognizable by their one oversized claw and one small feeding claw. Females and juveniles have two small claws. The males use their oversized claws to wrestle other males in territorial disputes and to send out intricate calling signals to attract females.

The fiddler crab forages for algae, fungus and detritus (decaying plant and animal matter), which is full of rich nutrients. It is believed that that the presence of this species is a bioindicator of a healthy marsh system. The crabs’ tunneling expertise aerates the mud, allowing for the expansion and growth of marsh grasses. Foraging techniques also assist in water quality improvements.

Semi-terrestrial fiddler crabs breathe air but must keep their gills wet in order for them to function. The species digs burrows, about one-half inch in size, that may go down a foot deep and connect with other burrows. This allows the crabs to make a speedy exit away from looming predators such as gulls, wading birds, fish or raccoons. The crabs live in large groups for protection. When a predator is sighted, an alarm goes out. Burrows also give haven from daytime heat and the sun. As high tide approaches, the fiddlers roll a ball of mud to plug the burrow entrance, leaving a pocket of air to breathe.

This unique marine creature is just one of the many inhabitants of Gooseneck Cove and is a testament to the continuing progress being made in the wetlands restoration. Migration Notes:

On Sunday, Aug. 31, at 8 a.m., Jay Manning will lead a free walk through the Norman Bird Sanctuary in search of migratory birds and other wildlife. Meet in the parking lot, bring binoculars, and wear sensible footwear.

Fall migration continues across Newport County and exciting observations are made every day. For the latest updates, visit the Audubon Society of Rhode Island’s website at asri.org or call 401-949-5454.

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