* Green shoots sprout on oil-coated marsh plants
* Hurricanes, high water could push oil into wetlands
* Scientists' initial "recon" suggests minimal impact
By Deborah Zabarenko, Environment Correspondent
BIRDFOOT DELTA, Louisiana, July 28 (Reuters) - Marsh grasses are the tough guys of the plant world. Left alone, they dominate coastal marshes from Texas to Newfoundland. Burn their stems and leaves, and they come back bushier than ever.
They help slow down hurricanes and filter pollution. As impenetrable to humans as a green wall, they shelter birds, fish and endangered mammals, and act as nurseries for commercial species like shrimp and crabs.
But let oil get into their roots and underground reproductive systems, and they can wither and die. If the grasses go, they could take parts of Louisiana's fragile wetlands with them, which means thousands of acres (hectares) of productive and protective marsh could turn into open water.
BP's (BP.L)(BP.N) Deepwater Horizon spill in the Gulf of Mexico has the potential for this kind of damage, and enough oil has coated some patches of marsh grasses to make them appear black when viewed from above.
Fortunately, their green shoots tell another story. Irv Mendelssohn, a wetland ecology expert who has been watching oil's impact on plants for three decades, offers a cautiously optimistic prognosis for their recovery from this latest environmental insult.
"There was a lot of fear before any data was gathered that this could be really damaging to coastal wetlands," Mendelssohn said after a one-day tour of marshes off Louisiana's southern edge. "As it turned out, we actually didn't see much oil. In fact, we didn't see any oil on the water's surface in the bays."
That doesn't mean there isn't any or that there won't be in the near future as material from the broken well continues to spread out. Wetlands aren't the only things in its path.
Environmental advocates worry about what oil treated with dispersant chemicals will do to birds, fish and other wildlife that come in contact with it -- and there are pea-sized rust-colored blobs of this material floating around the Birdfoot Delta, near where pelicans and gulls perch and feed.
Doug Inkley, senior scientist at the National Wildlife Federation, said it is simply too soon to tell what the BP spill's impact will be on the Gulf ecosystem, which ranges from deep-diving sperm whales to endangered Kemp's Ridley sea turtles to centuries-old coral reefs to the tiny phytoplankton at the bottom of the Gulf food web.
"Nobody really knows what's happening so far underwater, and it's a complex system," Inkley said. "You don't know which part of it you can knock out and not have a huge effect."
But to Mendelssohn, a professor at Louisiana State University's School of the Coast and Environment, the early evidence suggests that "marsh-oiling" may be a lot less extensive than initially feared.
GREEN SHOOTS ON OIL-BLACKENED STEMS
To conduct their survey of selected sites, Mendelssohn and two colleagues earlier this month launched an outboard-powered Boston Whaler from the marina at Venice, moving out into the eastern part of the delta.
The trio -- Mendelssohn, David White of Loyola University in New Orleans and Qianxin Lin of Louisiana State University -- set out at mid-morning for four hours among the reeds.
They knew just where to look, because federal SCAT teams (short for Shoreline Cleanup and Assessment Technique teams) have been ranging around the Gulf since shortly after the blowout, noting where oil has shown up. The SCAT surveys indicated oil on eastern sections of the Birdfoot Delta.
The tools the group used were simple: their eyes, their expertise and a camera. Mendelssohn and White dressed for the heat, in shorts, water shoes and caps; Lin looked ready to return to his Baton Rouge office, wearing long pants and a short-sleeved shirt. They had all driven hours to get to the delta on a simmering July day.
At each of four sites, Mendelssohn said, they were able to maneuver the shallow-draft boat right up next to the stands of grass, some of the reeds shoulder-high, others elephant-high.
They took no measurements and did not set foot in the marsh, recording what they saw in photographs, identifying what needs further study and observation.