CAUSE SOUGHT AS MARSHES TURN INTO BARREN FLATS

By Carolyn Y. Johnson, Globe Staff  |  July 17, 2006

PLYMOUTH -- A puzzling, ominously named phenomenon, sudden wetland dieback, is transforming salt marshes in the region into barren mudflats, scientists say, and their best efforts have failed to figure out why.

Across New England, researchers are poring over aerial photographs and slogging into mucky marshes on the lookout for ailing marshes, in hope of understanding its cause.

``It appears to us we have a new phenomenon we've never seen before," said Ron Rozsa, coastal ecologist at Connecticut's Department of Environmental Protection.

``It's raising red flags," he said. ``. . . How extensive is it? What is the cause? Will they recover on their own?"

Over the past five years, there have been reports of marshes that look as if they have been mowed . There are 17 suspected dieback marshes on Cape Cod, and a few other possible sites are on the North and South Shore, according to the Wetland Restoration Program of the Massachusetts Office of Coastal Zone Management.

Rozsa says dead patches are also visible on about two-thirds of Connecticut's shoreline. At least one report is from Rhode Island.

Research so far has been a frustrating exercise in what scientists call forensic ecology: reconstructing what happened to portions of dead marsh and preparing for the ecological repercussions.

``This great of an expanse of denuded salt marsh is not natural," researcher Sara Grady said recently as she paused, knee-deep in mud, in a barren expanse here that was once covered with lush cord grass, a salt marsh plant with a stiff, hardy stem. ``It's not typical," she said.

Scientists have little more than wild guesses about the cause. Some researchers in New England suspect it could be the result of a pathogen. In Louisiana and Georgia, it seems to be linked to drought. It could be linked to soil changes or changes in tidal flow, or it could be a natural process that has happened before, and the marshes may bounce back.

``It's really confusing," said Stephen Smith, a plant ecologist at the Cape Cod National Seashore. ``But people who have had long careers working in salt marshes, 40-odd years, think it's a very bizarre, unprecedented phenomenon."

The affected tidal marshes are one of the most productive ecosystems in the world. They are the basis of the food chain for many commercial fish species. They buffer the coast from storms, a concern sharpened by predictions of more hurricanes and the memory of Hurricane Katrina. They lie at an ecological frontline where they are sensitive to changes in both water and soil.

This summer, researchers with the state's Coastal Zone Management Office will be surveying 22 suspected dieback sites, most of which are located on Cape Cod.

There, erosion is a particular concern. Smith said that up to 6 inches of sediment appears to have eroded away in some marshes, leaving behind peat that looks like Swiss cheese. Fiddler crabs, Smith said, burrow happily on the mudflats left when the vegetation dies, but the food and shelter that support many of the marine creatures at the bottom of the ocean food chain are gone.

``When you see the peat falling apart, the Swiss cheese effect -- that's what's really scary," said Tim Smith, a wetland scientist with Coastal Zone Management's Wetland Restoration Program. If erosion changes the elevation of the marsh, ``we may be losing something that has taken hundreds or thousands of years" to develop.

Researchers studying patches of marsh turned to mud have been grasping for larger threads, and some have suggested that dieback is part of a global story.

In the 1970s, '80s, and '90s, Caribbean coral reefs suffered mysterious algal infestations, disease, and sea urchin die-offs. Researchers at the US Geological Survey put forth ``the dust hypothesis," which linked the reef declines to African dust storms, which have become bigger because of global climate change, changing land use, and regional weather.

Perhaps, says Rozsa, the African dust that could have carried nutrients, pollutants, and microorganisms to the reefs is doing the same thing to salt marshes. An analysis of the dust showed that it carries fusarium, a fungus known to harm plants, he said.

Wade Elmer, a plant pathologist at the Connecticut Agricultural Experiment Station who has begun taking samples of cord grass, said a species of fungus thought to be implicated in Louisiana's dieback resembles a species found in Africa and is working to identify fungus from New England plants.

But it's unlikely that anyone will find convincing evidence to prove the theory. Scientists studying the phenomenon say that dieback is probably the result of a combination of factors.

``. . .It's going to take a multifaceted approach [to unravel], studying the physiology, the hydrology, the pathology," Elmer said.

Elmer has been taking samples of diseased cord grass covered with lesions and yellowing blades to see if he can isolate the fungus and then infect healthy plants to test whether the fungus is really causing the plants to die or whether it is a red herring.

``We know what it looks like at point A and point B, but we don't know the process," said Grady, who uprooted a sample for Elmer and is recruiting volunteers to tramp into wetlands on the South Shore. She intends to check out potential dieback sites in Marshfield and to identify other places that are possible candidates.

The patchy dieback pattern, which seems to start at creek banks and then decimate random ribbons of cord grass, may be unlike that of other known causes of marsh grass death, such as ice shearing or suffocation by clumps of dead vegetation.

In Louisiana, 300,000 acres turned brown around the year 2000. In 2002, researchers noticed that about 2,000 acres of salt marsh in Georgia turned to mud, similar to what is happening in New England. But the Louisiana and Georgia marshes are growing back -- or at least not getting worse -- while marshes on the Cape don't seem to be recovering naturally, at least not yet.

Smith began transplanting test patches of healthy cord grass into sick marshes this summer, to see if transplantation will work. But even if the marshes start to recover on their own, things aren't resolved.

``To see marshes starting to be gone was really emotional for people," said Merryl Alber, a marine ecologist at the University of Georgia who has been studying Georgia's marshes. ``That's part of our coastal heritage. . . . I think that what was most upsetting to us was, we still can't go back and say, `Here's what caused this; here's what we don't want to see happening again.' "