Historical Trends and Drivers of Coastal Eelgrass and Algal Habitats over 40 Years in Washington State

Habitat-forming species such as eelgrass (Zostera marina) and algae (e.g. Laminaria spp., Sargassum muticum) play a vital role in the life-history of a wide range of marine species; they provide shelter for juvenile salmon, forage for migrating birds, and spawning habitat for herring. Despite the ecological importance of such foundation species, a lack of long-term data has limited our understanding of how the occurrence and abundance of these species has changed both spatial and temporally. We use a massive data set of spatially referenced surveys of nearshore vegetation collected by the Washington Department of Fish and Game (>100,000 observations) to provide a unique description of spatial and temporal patterns occurrence of nearshore vegetation types in Puget Sound, Washington (1972-2012). Across five regions in Puget Sound we demonstrate general stability in eelgrass occurrence throughout the time period. However, there is strong evidence for localized declines in eelgrass occurrence within each site that appear associated with changes to land use practices. In contrast, both Laminaria and Sargassum show a generalized increase in occurrence over the past 40 years. We discuss environmental and land use variables that affect each species.