Phragmites australis — or as most Louisianans know it, roseau cane — has a complex relationship with coastal Louisiana. In the Mississippi River Delta, roseau cane has existed for over 100 years and creates an essential barrier combating land loss in one of the fastest eroding portions of the state. However, there is a second variety of roseau cane that is invading coastal Louisiana marshes in other parts of the state.

In the southwest Terrebonne basin, roseau cane is quickly becoming the dominant pioneer species after marsh creation and restoration projects, both of which are very much needed in light of rapid land loss from erosion and sea-level rise. The spread of roseau cane may be good news for slowing land loss, as it is especially good at trapping sediment and reducing erosion. However, increasing abundance of roseau cane may block access for juvenile fishes and invertebrates that use the marsh edge as nursery habitat.

In 2024, Drs. Jeffrey Plumlee, Andy Nyman, Garrett Hopper, Megan La Peyre (USGS Coop Unit) and Theresa Davenport (post-doctoral research associate) were awarded funding to answer questions about increasing abundances of roseau cane in southwest Terrebonne. These questions included whether 1) habitat restoration increases the abundance of roseau cane, 2) abundance of roseau cane correlates with decreases in abundance of economically important juvenile fishes and invertebrates in southwest Terrebonne, and 3) densities of juvenile fishes and invertebrates at the marsh edge decline where roseau cane is abundant. In addition to answering these questions, the project is also supporting the graduate work of RNR graduate students, Emily Hura and Emily Robicheaux.

Hura’s thesis will use fishery-independent data collected by the Louisiana Department of Wildlife and Fisheries and the Coastal Wetlands Planning, Protection and Restoration Act’s Coastwide Reference Monitoring System to determine whether marsh edge use by juvenile female spotted seatrout, an economically important sportfish, is influenced by roseau cane density.

Robicheaux’s thesis questions involve estimating the densities of juvenile fishes along the shoreline with throw traps and trawls at sites that span the gradient of high to low roseau cane abundance. Considering the importance of maintaining and restoring salt marsh habitat to fisheries production in Louisiana, it is critically important to understand questions about how vegetation composition influences the quality of shoreline marsh habitats.

Graduate student Emily Hura, left, and postdoctoral fellow Dr. Yaolin Guo survey vegetation in a salt marsh.

Graduate student Emily Hura, left, and Emily Robicheaux trawl adjacent to the shoreline collecting juvenile fishes and invertebrates in southwest Terrebonne.