Eelgrass (Zostera marina L.) restoration in Puget Sound: development of a site suitability assessment process

Abstract

The restoration of eelgrass (Zostera marina L.) is a high priority in Puget Sound, Washington, United States. In 2011, the state set a restoration target to increase eelgrass area by 4,200 ha by 2020, a 20% increase over the 21,500 ha then present. In a region as large, dynamic, and complex as Puget Sound, locating areas to restore eelgrass effectively and efficiently is challenging. To identify potential restoration sites we used simulation modeling, a geodatabase for spatial screening, and test planting. The simulation model of eelgrass biomass used time series of water properties (depth, temperature, and salinity) output from a regional hydrodynamic model and empirical water clarity data to indicate growth potential. The geographic information system-based analysis incorporated results from the simulation model, historical and current eelgrass area, substrate, stressors, and shoreline manager input into a geodatabase to screen sites for field reconnaissance. Finally, we planted eelgrass at test sites and monitored survival. We screened 2,630 sites and identified 6,292 ha of highly to very highly suitable conditions for eelgrass-ample area for meeting the 20% target. Test plantings indicated that fine-scale data are needed to improve predictive capability. We summarized the results of our analysis for the majority of the approximately 3,220 km of shoreline in Puget Sound on maps to support restoration site selection and planning. Our approach provides a process for identifying and testing potential restoration sites and highlights information needs and management actions to reduce stressors and increase eelgrass area to meet restoration objectives. Implications for Practice• Simulation models in combination with a geodatabase and test plantings provided a comprehensive yet efficient approach for identifying sites suitable for restoring eelgrass in a large and complex estuary. • Our analysis showed that eelgrass restoration of 4,200 ha is achievable pending site-specific assessments, possible reduction in stressors, and following prudent restoration procedures. • The modeling and test planting identified fine-scale light attenuation data and improved physiological data, particularly in regard to low-light conditions and phenotypic or genotypic adaptations, as critical information needs to improve this method of restoration planning. • The model and database provide a methodology for assessing effects of climate and land use changes on species distributions and identify mitigation for these changes through stressor reduction and improved site selection.Author contributions: RT, JG, KB, AB designed the research and analyzed the data; JG, AB, JV conducted assessments and plantings; KB refined and ran eelgrass model; LA, JG conducted planner surveys; DW analyzed light data; TK contributed hydrodynamic modeling results; JK contributed initial model; KB, RT, JG, AB, JV, LA, DW wrote the manuscript.

Forty years of seagrass population stability and resilience in an urbanizing estuary

“…Additionally, some specific areas of eelgrass loss identified in our analyses have been previously identified by local experts (Thom et al . ) and increases confidence in our results.…”

“…Though the data we use were not collected for the purpose of monitoring eelgrass, we feel confident about our conclusions about eelgrass trends in Puget Sound as our basic trends post-2000 match a formal, stratified eelgrass monitoring programme initiated in the early 2000s (WDNR 2015). Additionally, some specific areas of eelgrass loss identified in our analyses have been previously identified by local experts (Thom et al 2014) and increases confidence in our results.…”

Integrating genetics, biophysical, and demographic insights identifies critical sites for seagrass conservation

“…The multiple types of analyses performed here provide guidance for agencies tasked with restoring eelgrass, as has been suggested in other areas of the world (Thom et al 2018).…”

Short Communication: Restoration of seagrass Enhalus acoroides using a combination of generative and vegetative techniques

“…Low survival rates when using generative techniques, on the other hand, have been caused by high failure rates in seed growth in the natural environment, due to the unsuitability of environmental conditions or seed predation (Orth et al 2002;Nakaoka 2002;Orth et al 2007). Therefore, site suitability assessment has been considered as an important step in selecting a potential restoration site for successful mass-scale seagrass restoration (Thom et al 2018).…”