Seagrasses perform important ecological functions: stabilizing sediments, providing essential fish habitat, and ameliorating local effects of ocean acidification through photosynthetic uptake of CO2. In spite of their acknowledged value, seagrass systems are declining throughout the world. The native seagrass, eelgrass (Zostera marina) in Washington State has been impacted by aquatic land activities and upland uses at some sites. There is an on-going effort to restore eelgrass ecosystems. However, because eelgrass occupies a wide range of environmental conditions and exhibits extensive phenotypic diversity, developing appropriate restoration strategies is challenging. It is not known to what extent phenotypic diversity reflects plasticity in response to prevailing conditions. It is also unknown to what degree populations can respond to perturbations. To develop informed restoration strategies for eelgrass in WA, we are investigating the degree to which phenotypes are influenced by environmental change. Our first phase of research examines the extent of local adaptation by performing controlled mesocosm experiments measuring trait responses to environmental variables, beginning with temperature and dessication on different populations of eelgrass. We manipulated 3 water temperatures: 10°C, 13°C & 21°C where 7 tanks were replicated for each temperature treatment. 3 shoots from three donor populations: Cherry Point (CP) and Fidalgo Bay (FB) and Willapa Bay (WB) were placed within each aquaria and assessed response over 2.5 months. We also investigated how air temperatures of 20°C or 25°C and desiccation events of 1 or 3 hours influenced eelgrass shoots from these locations with 7 weeks of recovery.
Results/Conclusions
We measured survival, plant morphology, wasting index and effective photosynthetic yield. Highest temperatures and longest dessication events significantly decreased survival of plants from all populations by >50%. Changes in plant morphology, wasting index and photosynthetic yield were also most significant in the extreme conditions, but the changes differed at each site. Among the three populations, WB plants showed least amount of leaf loss, CP the most, and FB plants leaf loss was mid range, WB plants had most lateral branching, CP the least and FB mid range. WB plants had lowest wasting index and smallest decrease in photosynthetic yield. CP plants has mid-range in wasting index and loss of photosynthetic yield, and FB plants were had the highest wasting index and greatest loss of photosynthetic yield. These measures of population-specific responses to stressors will provide insight into their productivity and survival in the face of changing environments and in turn will inform site-explicit transplantation strategies.