The Genetic Structure of Avicennia Germinans Populations in the Northern Gulf of Mexico

Around the world mangroves occupy around 152,000 km2 of tropical and subtropical coastline. Mangroves provide critical habitat for estuarine, nearshore, and terrestrial biota and supply crucial services such as shoreline establishment, protection from coastal erosion, coastal livelihood support and atmospheric carbon sequestration. The past and present-day distribution and abundance of mangroves in the Atlantic Eastern Pacific has been established through a combination of habitat suitability, climatic condition, and genetic selection. Mangrove species have been observed to be expanding poleward and landward across the Gulf of Mexico, where mangroves face the unusual situation of being both excellent at long-distance dispersal and constrained in any northward movement by available habitat. Though mangrove populations provide many crucial services, little is known about mangrove population genetic structure in the northern Gulf of Mexico.
The broad goals of this dissertation were to better understand global mangrove expansion at the cost of salt marsh habitat through literature review and to better understand Avicennia germinans phylogeography in the northern Gulf of Mexico by use of a modern next generation sequencing technique known as double digest RAD-sequencing. From the literature review, human activities both past and present were found to have significantly altered both salt marsh and mangrove habitat. Currently salt marsh habitat across the world is experiencing large habitat loss and fragmentation, while mangrove populations are expanding both poleward and landward. The current loss and fragmentation of salt marsh habitat along with the superiority of the mangrove species dispersal capability suggests that salt marshes across the globe are ripe for mangrove species encroachment and conversion. For mangrove phylogeography in the northern Gulf of Mexico, the genetic structure and the kinship of Avicennia germinans populations showed highly related populations with low genetic diversity and a high number of individuals with a similar genetic makeup. Taken together, the results of this study help to suggest future directions for mangrove conservation, mangrove genetics research, and the shift of the mangrove salt marsh ecotone in the GOM. Understanding the dynamics of these highly variable genetic relationships and the processes of genetic exchange in mangrove populations will be essential to predicting future impacts of climate change and anthropogenic forcing.