Award: OCE-1851043

Overview: Understanding how species cope with spatial variation in their environment is necessary for predicting how they may respond to environmental change. This project examined how key traits vary with depth and associated environmental gradients in light and temperature in the seagrass Zostera marina, one of the most important foundation species in temperate nearshore ecosystems worldwide. We paired experiments with fine-scale molecular analyses to examine the genetic and environmental components of seagrass trait variation. This work provided key information on the microevolutionary mechanisms that allow a foundation species to persist in a variable environment, and thus to drive the ecological function of whole nearshore communities. Graduate and undergraduate students were involved in all phases of the project, from experimental design to sample processing to data analysis and manuscript preparation. Key findings of the research were also incorporated into undergraduate courses and outreach programs for high school students from under-represented groups, and presented at local and national meetings of scientists and stakeholders. Intellectual Merit: This project documented that Zostera marina meadows that span a depth gradient experience rapid declines in light, temperature, and wave exposure with increasing depth. In addition, shallow meadows have greater shoot density, taller plants, and greater aboveground biomass than do deeper meadows, and they also tend to flower earlier. Mean dispersal distance, a key ecological parameter that influences both population demography and contemporary evolution, was estimated to be at a similar spatial scale (100-200m) as this observed scale of differentiation, suggesting that these depth-related phenotypic differences may reflect the outcome of local adaptation at microgeographic scales. Further, only a fraction of the shoots in an eelgrass meadow were estimated to contribute to the gene pool in each generation. The ratio of effective to census size in Z. marina is thus more similar to marine animal and algal species with high fecundities, mortalities, and variance in reproductive success than to terrestrial plants and animals. As a result, Z. marina beds may have less genetic variation to adapt to environmental change than is predicted from locally high abundance. Broader Impacts: A better understanding of seagrass dispersal and trait differentiation across depth is not simply a matter of academic interest, but also critical to successful seagrass restoration and conservation. The restricted spatial scale of dispersal suggests that local maintenance and expansion of these meadows is due to both clonal growth and localized seed dispersal. Although expansion to distant locations is possible, the rate at which new seagrass beds are colonized will likely be low without direct intervention and active restoration efforts, especially for those meadows in which seed dispersal is rare. Further, large numbers of individuals or a targeted selection of particular genotypes will need to be incorporated into these efforts to provide enough genetic diversity for adaptive responses to future environmental changes. To facilitate communication with seagrass managers, we participated annually in a regional seagrass conservation meeting that includes over 100 participants from federal and state resource managers, local conservation commissioners, academic researchers, non-profit representatives, to teachers. Data generated by this project were also used to develop undergraduate teaching modules that enhanced the learning experience of KSC students not directly involved in the project, and were made publicly available to other institutions. Project results were also shared with high school students through the Girls, Inc.s Beach Sisters and Eureka programs. Last Modified: 06/17/2024 Submitted by: RandallHughes