Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8700
Title: 40 years of seagrass population stability and resilience in an urbanizing estuary
Author: Andrew Olaf Shelton, T B Francis, Blake E. Feist, Greg Williams, Adam Lindquist, P. S. Levin
Publication Year: 2017
Journal: Journal of Ecology
Keywords: Eelgrass, Zostera, urbanization, nearshore habitat, coastal development, shoreline armoring, Salish Sea, Puget Sound, resilience,
Abstract:

Coasts and estuaries contain some of the most productive and ecologically important habitats in the world and face some of the most intense pressure from current and projected human activities, including coastal development. Seagrasses, in particular, are a key habitat feature in many estuaries and are perceived to be in widespread decline owing to human actions. Here, we construct spatio-temporal models to analyze a 41-year time-series consisting over 150,000 observations spanning 100s of km of shoreline in Puget Sound, Washington, USA to examine multi-scale trends and potential drivers of eelgrass (Zostera spp.) in an urbanizing estuary. At the scale of the entire estuary (100s km) we find a highly stable and resilient eelgrass population despite a more than doubling of human population density over the time period and multiple major climactic stressors (e.g. ENSO events). However, the aggregate trend is not reflected at the site scale (10 km), where some sites persistently increase as others decline. Site trends were spatially asynchronous; adjacent sites sometimes exhibited opposite trends over the same period. Substantial change in eelgrass occurred at the sub-site (0.1 km) scale, including both complete local loss and strong increase in eelgrass. Available metrics of local human development including shoreline armoring, upland development (imperviousness), and human density provided no explanatory power for eelgrass population change at any spatial scale.

Despite ongoing conservation concern over seagrasses worldwide, eelgrass in Puget Sound has been highly resilient to both anthropogenic and environmental change over the past four decades. Together our results suggest that the appropriate scale for understanding eelgrass change is smaller than is frequently assumed (on the scale of 1 to 3 km of shoreline) and contrasts strongly with previous work. Our work provides general methods that can be applied to understand spatial and temporal scales of change and can be used to both assess hypothesized drivers of change and identify locations of change for further study.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Describe the relationships between human activities and species recovery, rebuilding and sustainability.
Characterize the population biology of species, and develop and improve methods for predicting the status of populations.