Food web response to foundation species change in a coastal ecosystem

Abstract

In the Northern Gulf of Mexico, black mangroves (Avicennia germinans) are expanding their range and replacing smooth cordgrass (Spartina alterniflora) as the dominant foundation species in estuarine systems. The impact this habitat transition has on the sources of primary production that contribute to the food webs of these areas is as of yet unclear. Here, we used stable isotopes and Bayesian mixing models to determine the contributions of primary production sources to the food webs in Louisiana saltmarshes currently experiencing rapid mangrove encroachment. In addition, we determined how these contributions are altered as a function of foundation species cover, particularly for white shrimp (Litopeneaus setiferus). Species primarily rely on algae-derived and water-column derived production, not on production derived from the foundational macrophytes themselves. White shrimp trophic position increased in areas with higher mangrove cover at some locations; shrimp used more water column-derived production and less algae-derived production. Transition from Spartina to mangrove-dominated estuarine areas has little effect on the overall pattern of primary producer contribution to food webs in these areas. However, differences in the structural and substrate properties of these foundational species could be altering the way energy moves through food webs.