Five years ago, Hurricane Katrina devastated the Gulf region, killing nearly 2,000 and displacing more than 250,000 others from Louisiana to Florida. This week, in a series titled "Hurricane Katrina: Five Years After," FoxNews.com looks back on the costliest natural disaster ever to strike the United States.
Hurricane Katrina left the Louisiana coastline bruised and battered, ripping up and carrying away barrier islands that were supposed to protect it, pummeling marshes with walls of salt water and leaving the ecosystem of one of the world's largest and most valuable estuaries hanging by a thread.
Half a decade later, researchers still don't know for sure what will recover naturally and what will need help to heal.
"When you have events like Katrina and Rita, it totally changes your landscape," says U.S. Geological Survey ecologist Greg Steyer, who runs the coastal restoration field station for the National Wetlands Research Center.
Hurricane Rita hit the Gulf Coast just one month after Katrina, completing a one-two punch that put the Louisiana shoreline on its heels, wiping out an estimated 328 square miles of coastal land on what is the world's seventh largest estuary. Scientists using satellite and monitoring station data have been assessing the damage ever since.
Comparing the Louisiana coastline in 2008 to its appearance before Katrina, John Barras of the Louisiana Water Science Center said it was "equivalent to 26 years of loss with only one major land-falling storm."
The loss of coastal marshes and islands has been critical for several reasons. It has affected wildlife – Louisiana estimates that 5 million birds use the area as a breeding ground -- as well as all of the surrounding marine life, which supplies a quarter of the nation's annual seafood catch and accounts for about $2.4 billion a year in wages and sales, according to the Louisiana Seafood Marketing Board.
Wetlands are also critical to the area because they act as a filter, purifying groundwater and removing sediment and pollutants, and they protect coastal communities during storms by absorbing and deflecting inbound floodwaters.
Some of the most dramatic loss occurred in the Chandeleur Islands, a north-south chain of low-lying islands about 60 miles east of New Orleans. U.S. Geological Survey photos taken before and after Katrina show that whole islands were swept away. Some of these protective shores may return, others may not, Barras says.
In some cases, researchers expect that sediment may be re-deposited naturally and help recover some critical barrier islands and wetlands. But in other areas, particularly west of New Orleans, some fragile marshes were damaged down to their root zones, making it impossible to recover without some sort of restoration project.
"It's not black and white," Steyer says. There are a lot of interactions, including the effect of man-made levees that, ironically, can prevent some areas from recovering due to a lack of sediment deposits that usually occur during seasonal flooding.
The ecological damage extends inland. The Pearl River floodplain forests sustained 120-mph winds during Katrina that sheared off the tops of towering cypress and tupelo trees and decimated some areas. The state estimates that it lost 719 million board feet of timber valued at approximately $335 million dollars -- and that loss may be permanent.
While the natural cycle of storms along a coast can contribute to the richness and diversity of its wildlife, researchers fear that new invasive species are faring better now than local species along the Louisiana coast. Fast-growing Chinese tallow trees may replace slow-growing tupelo trees, depriving birds and wildlife of much of their natural habitat and changing the look of the classic southern cypress forests forever. Smaller but denser undergrowth could not only leave less space for birds to nest, but also reduce the habitat for deer and other wildlife on the ground.
Fishermen as well as scientists are encouraged that certain species of shrimp and oysters that saw their populations reduced by Katrina and Rita have bounced back. This summer, many fishing businesses expected to have catches that finally matched pre-2005 levels -- and then the BP oil disaster struck.
For scientists and researchers in the area, such disasters -- manmade and natural -- make it difficult to tell how much of the coast can recover and how long it will take. If hurricanes become more frequent and more intense in the region, as some researchers expect, the chances of the Louisiana coastline fully recovering will be even further reduced.
Restoration and protection work is clearly necessary to protect against future disasters. Even before Katrina, restoration planning was already underway. Nearly $2 billion was earmarked in 2004 for the Louisiana Coastal Area restoration project, and Steyer says six projects under that plan have been completed since 2006.
But further feasibility studies and larger scale projects are needed -- and they are complicated.
"You're trying to restore an ecological process, and the marshes respond very slowly," he said. "Our coast was built by the Mississippi River over thousands of years, so it's not going to come back tomorrow or next year."
And, he points out, it's not going to come back on its own.
John R. Quain is a personal tech columnist for FoxNews.com. Follow him on Twitter @jqontech or find more tech coverage at J-Q.com.