Salt Marsh Life

 

By Jennifer Barry Hawkes,  Charleston Post and Courier,  Oct. 6, 2003

The sun's dusky rays reach across a swaying grass carpet dotted with white egrets. Mud teems with skittish crabs that dart underground should you so much as take a deep breath. But inhale deeply anyway. Know the smell of life decaying into a fuel for all who live here.

It's the smell of the salt marsh, the scent of sea meets land, where ocean mystique gives way to pluff mud and cordgrass. Charlestonians have long associated the sights and smells of this rich ecosystem with home.

Salt marshes stretch just about anywhere you drive or boat around here. They define the landscape, force open green spaces and appear to be grassland or ocean, depending on the time of day.

They also are among the world's most productive ecosystems and natural pollution filters. They even provide nurseries for many commercially important species of crabs, shrimp and fish.

"A lot of what you get on your seafood platter spent at least part of its life in a salt marsh," says Whit McMillan, conservation education manager of the S.C. Aquarium, which has a salt-marsh exhibit.

Sometimes revered as the "cradle of the sea," marshes have stoked the imaginations of artists, photographers and poets.

Yet, they weren't always seen as the vistas of today.

Not so long ago, people drained them to control mosquitoes. It's easy to see why. An acre of salt marsh can produce 10 million mosquitoes in a good downpour, 80 million on an acre of dredge disposal.

"There's always been the misconception that salt marshes are so much wasted space, that if only you could pave over them. ...," says Elizabeth Wenner, senior marine scientist at the Department of Natural Resources.Indeed, people filled in marshes to build homes and grow crops. Half of the nation's salt marshes were destroyed, many from 1950 to the mid-1970s, according to the state DNR. Some states such as California allowed people to fill virtually all of their marshes so almost none remain.

But not South Carolina. About 80 percent to 90 percent of the state's original marshland remains. South Carolina is home to about 420,000 acres of salt marsh, among the most of any Atlantic Coast state (it competes with Georgia for No. 1 ranking), according to the U.S. Fish and Wildlife Service.

"The massive destruction hasn't occurred here as it has in other coastal states," Wenner says. "The key is recognition that salt marshes are important. The public has got to be vigilant and realize these resources are finite. You can't replant 300,000 acres of marsh."

Valuable as we know they are today, a salt marsh is a rough place to call home.

Defined by a twice-daily rise and retreat of the ocean, flora and fauna must bear huge changes in salinity and water depth. Tides can flood their world with 5 to 8 feet of water.

Referring to a salt marsh means several things. There are uplands dominated by deer and raccoon, the high marsh with its fiddler crabs and oyster beds and the underwater world teeming with fish.

"I think of it all as one system," McMillan says. "It's all so intertwined. There are just so many habitats there."

Yet, if one thing defines this world -- and who survives here -- it's the salt.

SALT LAND (AND WATER)

The farther they traveled in, the more the tide moved out and the water levels lowered. In some areas it drained away completely, exposing steaming mudflats where wading birds hunted for dinner in the soggy soil. Brett slowed their pace and the engine lowered to a bubbly growl as he expertly motored through the jungle of grass, his eyes on the bank, one hand on the rudder. It was like being Katharine Hepburn and Humphrey Bogart on the African Queen.

-- Mary Alice Monroe, "The Beach House"

The patriarch of the salt-marsh ecosystem is one adapted to the salty world: spartina alterniflora, or smooth cordgrass. A marshy grass expanse is spartina.

Among the plants here, spartina leads a lonely life. Few others can take the salt.

But this grass has adapted to its salty home. It boasts thicker cell walls and an ability to pump out some salt that it takes in.

Good thing for the ecosystem that depends on it. Spartina serves three critical roles: home, nursery and food source.

Few animals eat the actual plant, which reaches 2 feet to 9 feet. But living spartina converts huge amounts of solar energy into plant tissue. When it dies, pieces of grass decompose into detritus, a nutrient-rich load that mixes into mud and washes into estuaries to feed marsh residents and visitors.

Spartina also binds gushy mud and provides a place for birds to nest and reproduce. Marsh wrens, for instance, weave living grass to make their nests.

And with its tall, sturdy stems, spartina provides its guests a nice shelter.

Among them are gangly marsh hens that nest here and slip along spartina so well that people rarely see them. They sneak along the grasses dining on fiddler crabs and periwinkle snails. Also called clapper rails, they're the birds laughing -- or yelling -- at you when you pass by.

Spartina also helps endow the marsh with its crucial role as buffer. A 10-foot stretch of salt marsh can absorb most of a wave's energy. That eases the pounding on beaches, roads and homes from tides and boat wakes. It even helps absorb hurricane storm surge.

By definition, a salt marsh is a grassland flooded by ocean tides. But the marsh is far more than a sea of spartina. Life is most diverse below the ever-changing water's edge.

WATERY WORLD

I walked to the edge of the marsh. The full force of the salty air washed my face and, in an instant, I was a young girl again.

-- Dorothea Benton Frank, "Sullivan's Island: A Lowcountry Tale"

Salt fends off most plants here, but the underwater world that floods in and out of the marsh teems with life. Spartina plays special host, protecting flora with roots and stems and food-rich nooks and crannies that make a marsh the ocean's nursery.

The commercially popular croaker, white shrimp and spottail bass are among those who rely on the marsh to reproduce. Many species move into the marsh as vulnerable little guys and head into creeks and ocean as they grow. Other temporary residents include red drum, pin fish, weak fish, flounder, gray snapper, blue crabs, shrimp and spotted sea trout.

"That's why it is so critical to protect the little tidal creeks and marshes. It's important to have a bigger frame of mind," says Pam Cox Jutte, a DNR marine scientist. "So many species are moving all over the place."

With all these swimming treats come plumed predators. Herons and egrets, their stalk legs underwater, will spear anything from a fish to a baby alligator. Other predators include the once-endangered brown pelican, osprey and bald eagles. Birds of all feathers come to eat fish, crabs and snails. Even endangered wood storks thrive here, recovering from the habitat loss and other human tampering that nearly killed them off in the Everglades.

And when water retreats, many feathered predators turn their eyes to the exposed mud.

HIGH MARSH

The spirits urged me to roll down the windows and breathe the musk-laden drug of the marsh. The scents of plough mud and rotting marsh life filled my senses like a warm shower of rare perfume.

-- Dorothea Benton Frank, "Sullivan's Island: A Lowcountry Tale"

When the tide retreats, the soggy Earth seems empty, quiet. Then across the mud scurry up to 600,000 fiddler crabs per acre. When so much as a leaf blows by, they dart inside burrows to flee from danger.

The claw-waving fiddler crab is another species that's adapted to a salty world. Good thing.

They eat mud, and here it's rich in organic matter. And as they burrow, they loosen sediment and allow oxygen to penetrate dirt that otherwise could become void of life-sustaining oxygen.

In this part of the marsh, where water comes and goes, lives a mucky mix of microscopic bacteria, algae and fungi that consumes detritus. They, in turn, are food for snails, shrimp, oysters, clams, worms and fiddler crabs.

The diamondback terrapin, once almost eaten to extinction, is among the only reptiles in the marsh - and its numbers appear on the decline again. The turtles swim along creeks and climb onto land to nest. They provide food for predators and eat snails and fiddler crabs whose populations could surge without them.

But this high-marsh realm is defined by the oyster, a commercial favorite. They make a great meal for people, birds and otters alike.

The hard, craggy oyster beds also protect shores from erosion and create a hard floor in a soggy, coming-and-going water world.

Their crevices create habitats for crabs, fish, shrimp and worms. Even open-ocean fish venture to the marsh to breed and grow safely among the oyster beds. Oysters even filter and clean water.

"Oysters are a really important habitat," says Rachel Kalisperis, aquarist at the S.C. Aquarium. "If there's not something to settle on, they won't grow up or reproduce."

Yet, people eat them and throw away the shells. They knock oysters off reefs with boat wakes. And they let everything from pet waste to boat fuel to lawn fertilizer run into the marsh after a good rain.

And when oyster beds aren't around for the many species to spawn, so go those species and the ones who eat those species and so on through the ecosystem. But there is good news. As oysters have declined along the coasts, groups have stepped up to restore them. DNR staff, for instance, is working on a project to replant oyster shells.

"It's a really important habitat," Jutte says. "It's not just a bunch of shells."

MARSH'S EDGE

Along the uplands where the marsh fades to land emerges a world less salty and watery, where furry predators work the edge of the marsh. Oyster-loving raccoons hunt with possums, marsh rabbits, rats, mice and river otters. But all has not been good for the marsh's top predators. Wolves and cougars have been gone for 200 years. And no top predator means prey such as deer thrive unbalanced. In the past decade, coyotes have at least made an appearance.

Salt marshes nearly lost another top predator when toxins such as PCBs and mercury nearly killed off mink in local marshes by the 1990s. Today, DNR and Clemson University scientists are relocating some from Hilton Head back to local wetlands.

"Any time you have a top predator missing from an ecosystem, it's cause for suspicion," says Michael Thomason, horticulturist at the S.C. Aquarium.

The salt marsh, as with any ecosystem, thrives on checks and balances. That balance has endured through generations, creating lasting memories of pluff mud and swaying spartina.

The island is fringed with the green, undulating marshes of the southern coast; shrimp boats ply the waters around her and fishermen cast their lines along her bountiful shores. Deer cut through her forests in small silent herds. The great southern oaks stand broodingly on her banks. The island and the waters around her teem with life. There is something eternal and indestructible about the tide-eroded shores and the dark, threatening silences of the swamps in the heart of the island.

-- Pat Conroy, "The Water is Wide"

Credit: Of The Post and Courier Staff