Jeffrey D. Plumlee and Garrett Hopper

Louisiana’s fisheries are one of its greatest natural resources. The community of practicing fishermen and anglers is an essential part of Louisiana’s identity as a sportsman’s paradise. The strength of Louisiana’s fisheries is in its expansive marshland because of its ability to produce biomass that supports high fishery harvest. This marshland is shrinking as a result of land loss and erosion; however, there is concern that expansive restoration of marsh may introduce native species that have negative consequences on the value of marsh. Research led by a team at LSU AgCenter and Louisiana Sea Grant is investigating how an invasive species, Roseau cane (Phragmites australis), may be affecting restored marshlands’ value in producing new fishery biomass.

Marshes’ role as a nursery habitat for Louisiana’s fisheries has been investigated and verified for 50 years. For example, white shrimp (Litopenaeus setiferus), which has annual landings (a measure of fisheries production by weight) that often exceed 70 million pounds, are reliant on low-salinity marsh habitat where the densities of juveniles range from 4.6 to 13 times higher than in open water, according to a 1994 study of Texas marshes. A 1990 study of Texas bays found that blue crab (Callinectes sapidus), which have annual landings greater than 40 million pounds, are also strongly associated with low-salinity marsh habitat, with densities in salt marsh edges seven times higher than in unconsolidated mud habitat. Low-salinity marsh is also critically important for recreationally important fishery species, including spotted seatrout (Cynoscion nebulosus), southern flounder (Paralichthys lethostigma) and red drum (Sciaenops ocellatus), which are the most targeted species in this $3.1 billion industry that supports nearly 24,000 jobs across the state. By this measure alone, the economic impact and cultural value of Louisiana’s marshland are vast, which makes its protection and restoration so important to Louisiana stakeholders.

In Louisiana, about 25% of coastal marsh was lost between 1932 and 2016, according to the U.S Geological Survey. In addition to the loss of economically important species’ habitat, marshlands are critical landscape features that provide a variety of ecosystem services, including protection from storms and filtration of water. This loss of essential habitat has prompted widespread restoration along the Louisiana coast, including many areas where wetlands are being created or renourished through the capture and transfer of sediment. The Coastal Wetlands Planning Protection and Restoration Act, a federal law that provides funds for wetlands work, has overseen 16 marsh creation projects in the Terrebonne basin, the expansive marsh between the Atchafalaya River Delta and Port Fourchon. These projects enhanced 5,467 acres at a cost of $415 million since the first completed project, which was approved in 1993 and completed in 1999, according to the program website, lacoast.gov. The inherent value of estuarine wetlands far exceeds the cost to invest in them; however, it’s critical that Louisiana rebuilds marsh with the same efficacy — not only as storm protection or land created but also as habitat for marsh-dependent species.

Roseau cane (Phragmites australis; hereafter Phragmites) is a common marshland plant in Louisiana. In the Mississippi River Delta, Phragmites is essential due to its land-protection properties and has existed in the delta naturally for more than 100 years, researchers found in a 2011 study. However, there are non-native varieties of Phragmites that exist in Louisiana outside the river delta that are commonly colonizing restored wetlands. Successful marsh creation and restoration are contingent on the loss of placed sediment, which happens over time due to a variety of environmental factors. Phragmites is very good at retaining land and reducing erosion. This trait is necessary for places like the Mississippi River Delta, but it is contrary to the necessary processes for marsh creation. Stands of Phragmites are dense and can act as a hydrologic barrier (an obstruction to the flow of water) to the marsh edge, reducing the loss of sediment, which subsequently reduces the rate in which marsh creation projects degrade and age. This influences the strands’ function as habitat.

In addition to creating a hydrologic barrier that reduces sediment loss, Phragmites may also alter the access of fish and invertebrates to the marsh platform. Because invasive Phragmites may not serve the same role as other commonly studied native marsh plants, such as smooth cordgrass (Spartina alternaflora), there is a clear need to measure its value to fish and invertebrates as habitat. Some studies suggest that fish and invertebrates have reduced biomass in water-inundated Phragmites-dominated marsh when compared to water-inundated Spartina-dominated marsh, indicating physically-limited access. However, it is unclear if the same holds true for all fish and invertebrates, including white shrimp, blue crab and others that are among the most valuable to Louisiana’s economy.  

Researchers in the School of Renewable Natural Resources, including Jeffrey D. Plumlee, Garrett Hopper and Andy Nyman, along with USGS Cooperative Research Unit lead Megan La Peyre, have developed a project funded by the Water Institute’s Louisiana Center of Excellence to examine the potential differences between Phragmites-dominated marsh compared to Spartina-dominated marsh regarding their value to fish and invertebrates. The project consists of three components:

Investigate the perceived link between marsh creation and restoration and the abundance of Phragmites.

Correlate the long-term trends in the relative abundance of economically important species between areas with differing densities of Phragmites.

Use fisheries-independent sampling gears, such as throw trapping, trawling and minnow trapping, to examine fine-scale distribution and abundance of economically important species.

The work aims to inform industry and fisheries and habitat managers on the value of Phragmites as habitat to our living marine resources and the role that current marsh creation practices have in its propagation.

Jeffrey D. Plumlee and Garrett Hopper are both assistant professors in the LSU AgCenter School of Renewable Natural Resources. Plumlee also serves as the state fisheries specialist with the Louisiana Cooperative Extension Service and Louisiana Sea Grant.

This article appears in the fall 2025 issue of Louisiana Agriculture.

Graduate students Emily Robicheaux and Emily Hura oversee a trawl while looking for fish and invertebrates. Photo provided by Jeffrey D. Plumlee

Graduate student Emily Hura directs surveying with Yaolin Guo of the LSU School of Renewable Natural Resources and research technician Owen Henderson of the School of Renewable Natural Resources. Photo provided by Jeffrey D. Plumlee