Genetic Diversity and Structure of Natural and Restored Seagrass Meadows on the Eastern Shore of Virginia: Causes and Ecological Consequences

Genetic diversity is positively associated with plant fitness, stability, and the provision of ecosystem services. Typically, diversity is lost with disturbance and is not completely recovered by restoration. Therefore, there is concern about the state of seagrass genetic diversity in Virginia. Chesapeake Bay meadows are frequently disturbed, and coastal bay meadows were restored using Chesapeake Bay seeds. This dissertation assesses the genetic diversity of Virginia seagrass meadows and explores the processes influencing diversity and the ecological implications of that diversity. While I expected that historic and current disturbance in Chesapeake Bay would result in lowered genetic diversity, I found the opposite and instead showed, at three spatial scales, that disturbance shifted the balance towards sexual reproduction (opposed to asexual) and thus enhanced genetic diversity. Also counter to expectations, restored meadows maintained the high genetic diversity of donors, showing no signs of bottlenecks or genetic drift typical of restorations. Restored meadows were, in fact, more diverse than the meadows formed by metapopulation dynamics and recruitment from northern populations. Since the restored populations fit geographically into clustering models, I conclude that restoration did not disrupt regional genetic structure and instead simply accelerated recovery of both areal coverage and genetic diversity. Experimentally, I showed that increased genetic diversity results in higher seagrass density and ecosystem services (productivity, nutrient storage, and habitat) under a range of environmental conditions. Further, a survey showed that the influence of genetic diversity on seagrass ii density is comparable to environmental drivers (nutrient concentrations, temperature, and light availability), providing evidence that the positive relationship between genetic diversity and ecosystem functions, determined experimentally by manipulating plants in small plots and controlling for environmental variation, is applicable at larger spatial scales and under real - world conditions. Together these findings suggest that the great success, measured by areal coverage and the value of ecosystem services (worth an order of magnitude more than restoration cost), of the Virginia coastal bay seagrass restoration is due in part to the high genetic diversity of the system. Further, conservation and restoration programs in other regions would benefit from the inclusion of genetic diversity in monitoring and restoration.

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