Genetic aspects of resilience in the foundational seagrass Halodule wrightii: the role of genetic variation and gene expression in maintaining primary production

Seagrasses are coastal foundation species which significantly contribute to the primary production of shallow water ecosystems and provide several services. However, seagrasses, like other coastal foundation species, are threatened by myriad anthropogenic stressors. Conservation is difficult in ecosystems under multiple threats where the factors that contribute to production are not easily elucidated. Genetic diversity and gene expression may be related to the function and stability of populations but are rarely considered in management plans. High genetic diversity and the associated trait variation within a population are known to contribute to higher function and stability of a population. Additionally, individual-level changes in the expression of photosynthesis and stress related genes can trigger physiological responses during a disturbance and increase chances of survival. In Chapter 1, I review the relationship between genetic diversity, function, and stability in five coastal foundation species, in order to assess the current state of knowledge and inform on directions of study beneficial for seagrass conservation. The synthesis of 129 relevant publications indicated more instances of neutral to positive relationships between genetic diversity and function than negative ones. However, the research is limited to a few genera and relies on unreplicated observational studies lacking controls or baseline data. In chapters two and three, I turn focus to the seagrass, Halodule wrightii, an important foundation species native to the Gulf of Mexico, where genetic aspects are rarely studied in relation to conservation. I relate metrics of production to genetic diversity (Chapter 2) and gene expression (Chapter 3) in the context of abiotic variation. Genetic diversity was not associated with bed production metrics. Gene flow between bays was limited and beds exhibited significant isolation by distance and by environment due to temperature range. Abiotic variation was, however, associated with belowground biomass. In Chapter 3, measures of photosynthetic efficiency and the expression of stress and photosynthesis genes were positively related. These measures were also related to changes in abiotic variation that occurred after a hurricane. These findings provide insights on how best to manage and restore beds of seagrass and suggest genes that could be used as early indicators of stress.