Wetland salt marshes provide a truly unique foundation for marine wildlife.
The marshes also play a vital role in buffering the shore against flooding and storms.
But something is killing New England's salt marshes - including those here in New Hampshire.
As New Hampshire Public Radio's Amy Quinton reports, scientists studying the sudden wetland dieback are concerned and puzzled.
Salt marsh dieback at North Mill Pond in Portsmouth. (Courtesy David Burdick)
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Dave Burdick tromps through ankle-deep mud and into marshy fields.
Here what's called smooth cordgrass grows near New Hampshire's shore.
The professor of marine wetland ecology and restoration at the University of New Hampshire knows this area in Portsmouth well.
"We're standing on a marsh on North Mill Pond in Portsmouth and this is a created marsh as mitigation for expansion of the NH Port Authority."
It's hard to imagine this acre of marsh was created.
The cordgrass is now five to six feet high, and its seed heads blow naturally in the wind.
From a distance, it looks like it's in perfect health.
But Burdick says this summer he discovered something here that really surprised him.
He points to several barren patches of muddy earth.
"This would be classic sudden marsh dieback, you can see the stems are up, but they're all dead, and we have new plants coming in between them that seem to be trying to grow even though this area's been wiped out."
Burdick says he's seen sudden marsh dieback both on North Mill Pond and at Sandy Point Discovery Center on Great Bay.
The discovery worries him because the grass roots hold the marsh together.
"With these plants dying off and having large areas exposed especially at the lower edge this is a spot now that will not collect sediments as rapidly because those plants aren't there to help collect, it won't build roots and rhizomes underneath, and when the ice comes, it will have a much easier time shearing that off and eroding the site."
Salt marshes are New England's grasslands and one of the most productive ecosystems.
Losing a marsh means eliminating the habitat and food for all kinds of life - fish, crabs, worms, and ribbed mussels, to name a few.
Burdick picks up a ribbed mussel nearby.
"These mussels live up to about seven years in age, these mussels want to be attached to an alternaflora shoot but all the alternaflora died here, so they're just lying on the surface."
Salt marshes are delicate and can die for all sorts of reasons - from pollution and drought, to grazing geese and tangles of dead plants called wrack.
But so far, scientists have ruled out the typical explanations.
The dieback is now affecting the coasts of all five New England states.
And it seems almost every scientist studying the problem has a different theory about why it's happening.
Salt marsh dieback at Sandy Point Discovery Center on the Great Bay. (Courtesy David Burdick)
What makes it even more puzzling; the cordgrass is starting to grow back in some areas.
But at Cape Cod National Seashore, plant ecologist Stephen Smith says about 8 to 10% of the marshes, mostly on the bay side, are dying.
"This year Wellfleet marsh out on Middle Meadow on Great Island we discovered plants turning brown and dying right in the middle of growing season in July and so that's sort of a first, we hadn't witnessed that before."
Smith says dieback is occurring over all parts of the marsh, in different species of grass, in areas close to urban development and those far removed.
Smith has spent part of his summer transplanting cordgrass to see if he could develop a reason for the dieback.
But he's had no luck.
"I've become more confused about it because interestingly enough you can collect soil areas where plants have either already died back or are dying back and take them back to the greenhouse and grow plants in them just fine so that's a bit confusing, in addition some of the transplants I've put out into areas that are dying back are also doing fine."
Smith says the plants may be stressed by multiple environmental and biological factors.
"A plant may show physiological decline, it's stressed and then things like fungi, aphids, and plant hoppers take advantage of that and probably accelerate their demise thereafter."
One coastal ecologist suggests that the dieback is part of a much bigger global change.
Ron Rozsa with Connecticut's Department of Environmental Protection notes that US Geological Survey Scientists have already hypothesized that Caribbean reef decline is due to pathogens from African dust storms.
Those storms have become bigger because of global warming.
Rozsa says perhaps African dust is carrying pollutants which are destroying salt marshes as well.
"That made me think well why couldn't that be the source of a potential new fungus to North America because it does seem that this is a new phenomenon that we can't explain by classical causes of vegetation loss in our tidal marshes."
Rozsa says one of the state's pathologists has isolated a fungus from Sudan, but has not yet proven whether it is disease-causing.
"I think in New England the jury's still out as to how severe this is."
Mark Bertness, a biology professor at Brown University thinks people are overly concerned about New England's salt marsh die off.
"They should be concerned that we don't understand what's going on first, I think"
Bertness says scientists simply don't have enough knowledge about salt marsh ecology.
He's been studying the die off on Cape Cod, and says something as simple as a small nocturnal crab called the sesarma reticulatum, or purple marsh crab, may be playing a role.
The little guys like to munch on cordgrass, and Bertness says ecologists haven't paid much attention to them, until now.
"There's a long standing belief among New England marsh ecologists that herbivores or consumers don't really play much of a role in salt marsh systems, which these episodes may be telling us is not true."
Bertness says the purple marsh crabs have been found all over Cape Cod - and they can move as far north as Maine.
But UNH ecology professor Dave Burdick isn't convinced.
Having grown up on the salt marshes, he thinks everyone should be concerned about these fragile ecosystems.
"To have this plant be so productive and so important to us its just an amazing thing that people should think about and care about and realizing that it's under threat is something of concern."
New Hampshire Department of Environmental Services is hoping to get volunteers familiar with the state's salt marshes to do surveying this weekend.
They want people to help look for sudden wetland dieback in other areas of the state -- to help determine how big a problem it is.
For NHPR news, I'm Amy Quinton.
