Ecosystem services of the food web along a salinity gradient in Louisiana marshes

Background/Question/Methods . Gulf of Mexico estuaries are among the world's most productive, with landings of commercially and recreationally important species exceeding all other areas in the US. Louisiana’s coastal wetlands are disappearing at an alarming rate. A remedy is to re-route Mississippi River water to supply sediments to rebuild vanishing wetlands. However, the response of native flora and fauna to freshwater inputs remains unknown.

We conducted a rapid ecological assessment of West Point a la Hache, Naomi, & Bayou Lamoque adjacent to the river, in 2015 & 2016. The marsh is fresh at the point of contact with MR but becomes more saline as it approaches Breton Sound in the Bayou Lamoque marsh and more saline in tidally-influenced marshes.

The objectives of our research were to use fish, ants, birds, and plants as indicators of marsh health, succession, and success and to use this dataset as building blocks for developing a model of marsh productivity restoration.

Results/Conclusions . Fish diversity varied significantly among diversions and salinity zones, with high salinity zones in each diversion and the low zone at Naomi harboring high diversity. Fish communities were found to be significantly different in traps among salinity zones with high salinity zone having different fish communities than low and mid zones, whereas mid and low zones were not.

An analysis of similarity indicated that bird communities varied little among diversions or salinity zones. The most commonly observed birds were boat-tailed grackle, blackbird (Brewer’s and red wing), pelicans, egrets, clapper rails, terns (Foresters and Caspian), laughing gulls, swallows (northern rough wing), seaside sparrows. Comparisons of diversity indices indicated that while not significantly different, lower salinity zones tended to have more richness. The mobile nature and large territory of many birds may contribute to the lack of differences detected in community and diversity metrics.

Preliminary analyses indicate that the diversity of environmental characteristics (e.g., salinity) provided by freshwater influence may enhance the biodiversity of fishes (and plants) at a relatively small spatial scale (<8.5km). Birds are not influenced by salinity changes at the scale of this experiment. There were significant differences between the species of fish found in low and high salinity waters. Only one type of plant, Ipomea, was similar between the two salinities resulting in highly significant differences. Ongoing research is vital for promoting the continued stewardship of coastal resources, especially given the nature and scale of proposed river diversions in the area