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Effects of Rouseau Cane on Coastal Wetlands

For almost a quarter century, Loyola University New Orleans biologists and ecologists Donald Hauber, Ph.D., Craig Hood, Ph.D, David White, Ph.D., and several undergraduate honors students, have studied the origination and effects of the common reed known locally as Rouseau Cane on the marshes and coastal wetlands of southeast Louisiana.

Their findings, which detail the spread of this plant and its role in coastal protection, is found in a published study, “Genetic Variation in the Common Reed, Phragmites australis, in the Mississippi River Delta Marshes: Evidence for Multiple Introductions.”

“Rouseau Cane has dramatically increased in the coastal wetlands along the Atlantic and Gulf Coasts during the past century,” White said. “The species’ spread is mainly due to the introduction of new gene types from Europe. These invasive types are becoming more common in the interior marshes of the Mississippi River Delta, land that is extremely rich in nutrients.”

The Mississippi River Delta covers an area roughly 521,000 acres, but during the last 40 years, it has been significantly reduced due to lack of river sediment coupled with high natural subsidence.

P. australis is the dominant emergent vegetation in the Delta’s outer two-thirds and is believed to play a major role in stabilizing these extensive marshes by breaking wave action and storm surges from the open Gulf while also capturing and retaining river sediment. “This stabilizing role protects the diverse interior marsh communities that provide food and breeding habitat for wildlife, particularly birds,” said White.

In recent years however, the new European gene types of P. australis, have begun to expand into the interior marshes displacing food and habitat resources for wildlife. This new invasion into these inner marshes is thought to have negative impacts on sustaining the migratory and local wildlife.

In the study, Hauber, Hood and White identified several new DNA types of P. australis which were likely brought here by migratory birds, river currents or ships. These European types are increasing the species’ footprint in the delta at an alarming rate, according to White.

The researchers have been monitoring the spread of the Rouseau Cane through aerial views of the wetlands to study the impact from above. 

White noted the massive impact of Hurricane Katrina on the wetlands. “Flying over the coast and the Mississippi Delta, it is a terrifying and powerful image because of what is no longer there and it proves to me that the city is more vulnerable to another significant storm surge than I previously imagined. If every citizen of Louisiana had this kind of flight opportunity, we’d be moving much quicker and with far more attention to protecting and restoring our coast.”

Flights have confirmed that the invasive types of P. australis is spreading throughout their research sites in the inner marshes of the delta. In a similar flight during the spring of 2006, White observed small areas of the invasive P. australis that are now much larger and spreading to other areas outside the delta. The Deepwater Horizon Oil Spill caused some coastal wetlands loss along the very margins of the delta’s shoreline, according to the researchers. "The total wetland loss in the delta is remarkably low as a result of the spill, though any loss is very troublesome,” White said. “The small amount of loss is partly due to the freshwater sheet flow that kept oil away from the delta freshwater wetlands, and partly because of the peripheral stands of the P. australis which became the frontline physical barrier to oil invasion inland.”

White, Hood and Hauber use photo images from wetland fly-overs to continue studying P. australis in their study areas. “The study of P. australis is central to the health and stability of the wetlands of the Mississippi River Delta,” said White.

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