The range of black mangroves (Avicennia germinans) is projected to expand in the northern Gulf of Mexico due to reduced winter freeze events. The colonization of mangroves in salt marshes alters habitat structure and creates a novel basal carbon source for consumers. While large scale shifts from salt marsh to mangrove are predicted in Louisiana with potential increases in winter climate, there is minimal knowledge of estuarine faunal response. To determine the aquatic faunal community response, in 2016 we studied two sites in coastal Louisiana with three habitat types, marsh-dominated, mangrove-dominated, and a transition or mix of the two. Juvenile nekton and epifauna were collected via suction sampling and analyzed for community composition and density to determine habitat use. Basal carbon sources (emergent vegetation, phytoplankton, macroalgae, benthic microalgae), soil organic matter, and common aquatic consumers ((blue crabs (Callinectes sapidus), brown shrimp (Farfantepenaeus aztecus), grass shrimp (Palaemonetes spp.), Gulf killifish (Fundulus grandis), periwinkle snails (Littoraria irrorata) were collected at each habitat type, measured using bulk stable isotope analysis (δ13C, δ15N, δ34S), and assessed using Bayesian mixing models to identify basal carbon sources and determine if mangrove carbon is incorporated into salt marsh food webs.
Results/Conclusions
While data analysis is ongoing, preliminary results indicate that juvenile nekton and epifauna community composition and density change with habitat type, three taxa (Amphipoda, Tanaidacea, and Caridea) drive these differences. The extent of difference between aquatic faunal habitat use is largely dependent on location. Conversely, most aquatic consumers relied on a mixture of microphytobenthos, suspended particulate matter, and Spartina. Overall, microphytobenthos was estimated to have the highest contribution to aquatic consumers regardless of habitat or location. However, the marsh periwinkle did reflect a change in basal carbon source with habitat. The carbon source shift in this deposit feeder is likely a result of concurrent differences in soil organic matter among habitats. These findings indicate variation in aquatic species and community response to mangrove expansion. More research is necessary to understand how continuously changing factors, such as elevation and inundation, productivity, and resource availability may influence Louisiana’s valuable estuarine communities spatially and temporally.