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A Blue View: In the Mud

Don’t be deceived by the desolate look of a mudflat. These areas of mud or sandy mud, which line thousands of miles of Chesapeake Bay shoreline, are hiding a rich variety of life.

Published June 02, 2015

Also known as intertidal flats, mudflats are the stinky result of fine sediments combining with organic matter, water saturation and bacterial influence. They’re affected by the rise and fall of the tide, creating various microhabitats as they’re submerged and exposed. 

Though much of this ecosystem’s activity is hidden from view, you’ve probably seen evidence of its inhabitants if you’ve ever stepped foot onto its soft and slimy surface.

Fiddler Crab

The tiny holes commonly found in mudflats are likely the work of an invertebrate like the fiddler crab. This animal digs burrows along the higher intertidal zones, emerging at low tide to snack on detritus and microalgae. When the tide rises once again, it creeps back into its burrow and plugs it, sealing itself inside, safe from predators. 

Moon Snail

You know those shells you find along the coastline that have perfectly circular holes through the top of them? Spoiler: That hole was no accident. It was made by a snail, such as an Atlantic moon snail. This unusual mudflat inhabitant preys on smaller snails by using its tongue-like radula to essentially drill a hole through another snail’s shell and then slurp up its prey. See one for yourself—or better, touch one—at our newly open exhibit, Living Seashore. 

Blue Crab

Visitors to the Bay have a good chance of stumbling upon a discarded crab shell while combing the shoreline. There’s a reason they end up there. Blue crabs wait for the tide to rise, and then move into the mudflat’s safe, shallow waters before shedding. 


The intertidal flat’s plethora of worms, amphipods, clams and snails make it a haven for commercially important fish that feed on them and use this habitat as a nursery ground. Striped bass, white perch, menhaden, anchovies, American eels and others are just a few species taking advantage of this seafood buffet. 

Great Blue Heron

Where you find fish, you’ll find birds. If you’re lucky, you’ll spot one of these majestic birds wading in the water. Their presence is a sign of life in the shallows—they’re waiting patiently to grab their next meal. Fish, insects, frogs, crabs and even mice contribute to the great blue heron’s diet.

Episode Transcript

Don’t be deceived by the desolate look of a mudflat. These areas of mud or sandy mud, which line thousands of miles of Chesapeake Bay shoreline, are hiding a rich variety of life.

Put your sturdy hip-wader boots on, because today we're wading into ... the mud. If you’ve spent any time on the Chesapeake Bay, you’ve felt mud between your toes. That’s because our watershed consists of miles and miles of mudflats.

The mudflat habitat, sometimes called a tidal flat, is an enclosed coastal area with fresh- and saltwater saturated sediments. It is the tidal low end of a salt marsh.

It’s also a fertile edge, a boundary between the terrestrial upland, the estuary and the open ocean—and it’s very much alive. Mud’s brown, green and gray fine silt sediments are literally teeming with life: algal, microbial and animal. There is much burrowing, hiding, fishing, darting and diving going on.

It’s anything but yucky to the biologists who study it. To them, mudflats are fascinating—because they’re full of biomass.

Microphytobenthos are part of that biomass. These are organisms like unicellular algae, which are responsible for the subtle brown and green shading you see in mud. They are the primary producers of that ecosystem.

Other vegetation, such as salt marsh grass, contributes to the variety of life found in mudflats. These wetland plants cover the salt marsh upland of a mudflat, and their roots function as mud-stabilizers. When these grasses die and decay, their decomposition provides rich organic nutrients—and with it, rich, organic muds, which provide excellent compost for the seeds of new plants. And the circle goes around.

Fiddler crabs, snails and more than 300 other species of invertebrates are, themselves, food for many species of migratory birds along the Eastern Flyway and for wading birds, such as the iconic great blue heron and snowy egret.

In the early 1900s, Chesapeake mudflats had such abundant populations of oysters, clams and mussels, it was estimated the entire volume of the Bay was filtered every three to six days. A single oyster can filter 50 gallons of water a day, and these bivalves were the foundation of a great commercial fishery, and the Bay's water-cleaning system.

These days, according to the latest data from the National Oceanic and Atmospheric Administration, the oyster population in the Bay is “less than 1 percent of what it once was” due to habitat destruction, pollution and disease. It now takes the current oyster population about a year to filter that same amount of water that it used to do in a day.

Restoring mudflats is a priority. Here in the Chesapeake, they’re protected in such places as the Blackwater National Wildlife Refuge on the Eastern Shore. But, as a fragile and scarce habitat of only about 45,000 square kilometers worldwide, they need greater protection.

Despite their rarity, mudflats and their associated salt marshes are some of the most productive marine habitats on Earth. They even boast specialized bacteria that thrive in the thick, anoxic mud—which sometimes contributes to its eggy gaseous smell.

According to the Maryland Commission for Climate Change, which predicts a 2.1-foot sea level rise by 2050, sedimentation patterns will change, and salt marsh and mudflat ecosystems will creep landward.

In addition to providing nursery habitat for the fish, crustaceans and shellfish we like to eat, mudflats also serve as a buffer. They slow erosion, acting as a sponge for storm surges. They protect our coastal communities. Mud—silty, soft, squishy and always dynamic—is the protective habitat between us and the great blue sea.

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