The ecological consequences of mangrove expansion into salt marshes on the Texas (USA) coast

Dr Anna R Armitage¹, Sean Charles², Rachael Glazner¹, Janelle Goeke¹, John Kominoski², Carolyn Weaver³, Ashley Whitt⁴, Steven Pennings⁵

¹Texas A&M University At Galveston, Galveston, United States, ²Florida International University, Miami, United States, ³Texas A&M University – Corpus Christi, Corpus Christi, United States, ⁴Deakin University, Geelong, Australia, ⁵University of Houston, Houston, United States

Climate change is driving landscape-scale shifts in plant species distributions and abundances, subsequently altering ecosystem structure and function. Such shifts are occurring along the Texas Gulf Coast (USA), where increases in temperature minima have led to mangrove encroachment into salt marsh wetlands. Partly in response to this regime shift, coastal managers in this region have increased the use of black mangroves (Avicennia germinans) in restoration projects. However, it is unknown if this adaptive approach will yield appropriate ecological outcomes. Here, we synthesize results from a series of surveys and field experiments that quantified some ecological consequences of mangrove restoration or establishment in novel areas. Generally, marsh plant cover and diversity were inversely related to mangrove cover. Within marsh or mangrove stands, benthic epifauna and nekton densities were generally similar, but mesocosm studies revealed that mangrove leaves are less palatable to basal consumers. In addition, mangrove aerial root structures decrease predation success on shrimp and snails. Citizen science data records indicate that shorebird and wading bird species richness and diversity were higher in marshes than in mangrove areas. Mangroves increased aboveground carbon and generally increased overall carbon retention in the soil. In addition, mangroves attenuated labile wrack accumulation, thus altering the trophic availability of allochthonous carbon. Overall, this uniquely synthetic body of work revealed that salt marshes and mangroves support different plant and animal assemblages, and that the establishment of mangroves in novel areas is likely to cause complex changes in ecosystem processes.

Biography:

Dr. Anna Armitage completed her Ph.D. in Biology in 2003 at the University of California Los Angeles and is currently an Associate Professor of Marine Biology at Texas A&M University at Galveston. Dr. Armitage is a community ecologist with research interests in food webs and coastal habitat restoration. The ultimate goal of her research program is to use an understanding of coastal ecosystem ecology to improve restoration success in marsh, mangrove, and seagrass habitats.