Interpreting the salt marsh

“Where’s the beach?”

When I worked in New York City, I brought a new park ranger to see the salt marsh at Great Kills Park on Staten Island. He remembered going to the broad sand beaches there when he was younger. I showed him a place where the beach had eroded to an abrupt dirt slope. A few feet below was the leading edge of a growing salt marsh. When he looked out at the narrow green ribbon that had once been a hundred yards of sand beach he said with horror, “My God, look at the destruction!”

It was like being slapped. As a park ranger, I never looked upon a salt marsh as a scene of pity or an object of contempt. I explained to him that since six miles of marshy shoreline were filled in long ago to make swimming beaches, the reemergence and rapid growth of this little spot was nothing short of miraculous. But it opened my eyes to the second-class status a salt marsh is often assigned by seashore visitors.

Mississippi sometimes seems like a world away from New York City, but the same thing happened to its salt marshes. The Mississippi Gulf Coast boasts 26 miles of man-made beaches, the longest such stretch in the world. But the great beachfront was constructed at the expense of the 26 miles of tidal marshes. The marshes took a back seat to flood-control measures, and then to tourism development. Davis Bayou at Gulf Islands National Seashore is a small haven for the coast’s retreating salt marshes.

“Where’s the beach?” is asked so frequently at the Mississippi District’s visitor center at Davis Bayou that the rangers posted a sign with directions to the nearest sand beach. The name of our national park, Gulf Islands National Seashore, attracts travelers in search of snow-white sand and clear blue surf. But our Gulf beaches are on offshore islands, accessible only by boat. Imagine the disappointment of people arriving at Davis Bayou only to find its murky, fecund waters.

“Can I see the Gulf of Mexico from here?” a bewildered camper from Missouri might ask.

“Well,” I’d say, feeling a little like P.T. Barnum, “you can see Davis Bayou from here, which is where it all begins.”

Experiencing a salt marsh

Walking to a salt marsh may not involve crossing any great distance as much as it involves making a short vertical descent. When I bring people to the salt marsh at Davis Bayou, I ask them to observe the conditions around them and how they change as we walk through the upland woods and down into the marsh. For this we need only our five senses. No fancy or expensive scientific equipment is involved. The woods are shady, humid, and sheltered from the wind. The firm, uneven ground might be damp from recent rains or it may be dry, but it always has lots of leaves, needles, and other broken bits of woodland mixed in. There are many different types of trees, shrubs, and vines. Squirrels and woodpeckers can be heard moving among the branches and undergrowth.

The conditions are different in the salt marsh. Instead of tall trees and thick shrubs, there is a dense, flat, grassy field. The marsh is exposed to the sun and wind, so the air feels drier. You can taste the salt and smell the mud. The ground is either very wet or underwater. Statuesque herons and boisterous kingfishers frequent the marsh looking for food.

The closer you get to the marsh from higher ground, the more tolerant the plants are of salt water and tides. Occasionally, a tree will grow too close to the high tide line and get “burned” by a stormy surge of seawater, leaving only a dried stalk. You have arrived in the marsh when you find plants suited to regular contact with salt water and flooding by high tides.

You may also know you have arrived because you are losing your shoes in putrid, ankle-deep muck.

Marshes smell bad. The mud of Davis Bayou is a viscous, charcoal-colored sludge that smells of old eggs. It’s perfect for growing lush, wet meadows of marsh plants, but is inhospitable to explorers. Trampling the grasses to keep our feet clean and dry is bad for the marsh, so we stay on the boardwalk. It is every visitor’s responsibility to keep the salt marsh intact for the next group of inquirers.

Looking at the marsh from a boardwalk is fine way to see the marsh, but not a great way to experience it. I bring bits of the marsh up to the dry ground and let people experience it from there. Pass around a tray of fine marsh muck and take a look. Inhale its perfume deeply and smear it around with your fingers. Most adults won’t do it, but if you are a nine-year old or a marsh plant, you’ll love it. Unappetizing as it is, the marsh soil is rich in detritus (decaying plants and animals) and nutrients brought by the tides and by rain runoff. Excess nutrients are exported to the rest of the seashore with the tides and by migrating animals. In other words, the mud is food for life in the marsh and for the seashore beyond it.

The most common plant growing in the Davis Bayou mud is salt marsh cord grass. It is the most tolerant of salty flood tides and is found at the lowest elevations of the marsh. Its roots are specially adapted to draw fresh water out of the salt water. The cord grass secretes from its leaves the little bit of salt the roots absorb. Run your finger up a blade grass and then taste it. Salty, right? Plants that can’t do this are not found in the marsh. Upland plants stop and marsh plants begin where the water gets too high and too salty too often. The border between upland woods and salt marsh at Davis Bayou is very abrupt, and is defined mainly by the spring (highest) high tide line.

Cord grass is not the only consumer of detritus-rich soils. Periwinkle snails climb the stalks of the marsh plants to graze on algae and detritus. They are easily found and easily borrowed. If you pick one off a plant, it retreats into its shell. Hold it in your hand for a while and it will probably emerge to look for food again. You’ll feel it pushing itself along a slimy trail, sucking your skin with its raspy tongue. When you get sick of that, make sure you put the snail back where you found it.

You can learn a lot about an animal just by looking at its body and how it behaves. If you can catch them, compare a fiddler crab with a blue crab. Both live in the salt marsh but use it in different ways. For example, think about where you found each crab. Small fiddler crabs live in mud holes on the shore and come out to dash around only when the tide is out. They use their small claws to scoop up mud and eat detritus. Larger blue crabs stay in the water almost all the time. Each has a paddle-like pair of hind legs for swimming and large claws for catching and eating smaller animals.

Like many other creatures, blue crabs are only part-time marsh dwellers. They come to the salt marsh to fill a seasonal need for food or shelter. The commercial shrimp species of the Gulf of Mexico come to spend their adolescence hiding in marsh mud and getting fat on detritus. They swim out to sea as full-grown adults to be caught later for casino buffet spreads. Migratory fishes and birds are also found in and around Davis Bayou’s waters in the spring and fall.

I want Davis Bayou’s human visitors to consider why this unglamorous little tract of Mississippi’s mainland is preserved along with the sandy barrier islands that make up Gulf Islands National Seashore. As a highly productive habitat, the salt marsh serves the plants and animals of the greater seashore by producing food and providing shelter. Davis Bayou is in a national park because people care about protecting this part of the Mississippi Gulf Coast’s salt marshes. A salt marsh may be less fun than a beach, but its is much more interesting than a parking lot.

Biographical

I grew up on Long Island, New York. I have worked as an interpretive park ranger for the National Park Service in New Jersey, New York, Maine, and Mississippi since 1997.

References

Daiber, Franklin C. Animals of the tidal marsh. New York, 1982.
Lippson, Alice Jane and Robert L. Life in the Chesapeake Bay. Baltimore, 1984.
Pomeroy, L.R. and R.G. Wiegert, editors. Ecological Studies 38: the ecology of a salt marsh. New York, 1981.
Teal, John and Mildred. Life and death of the salt marsh. New York, 1969.

January 11, 2004. This is an excerpt of an article co-written with Mike Aymond and published in Current, the journal of the National Marine Educators Association, Vol. 20, No. 3. Courtesy of the National Park Service.

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Adam

Adam's artificial habitat is my official website and blog. I write as often as I can, so it is the best way to keep up to date on my goings-on.

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