The influence of land use on the nearshore pelagic foodweb

In the oceanographically diverse and urbanized fjord estuary we know as greater Puget Sound, our scientific understanding of pelagic ecology is poor, and systematic monitoring and assessment of living systems has long been neglected. Improved understanding of biological responses to our human footprint is needed to predict the response of the pelagic ecosystem to human actions. In this talk, we examine existing spatial and seasonal patterns of Puget Sound’s nearshore pelagic foodwebs measured along natural and anthropogenic gradients. We tested whether abiotic and biotic metrics were sensitive to land use activities (urbanization and agriculture) in the catchments surrounding sampling sites in nearshore pelagic waters. To address this question, we conducted a large survey effort (monthly sampling of 79 sites from April to October) in 2011 examining multiple foodweb components in nearshore surface waters of six oceanographic sub-basins of Puget Sound. We observed strong spatial and seasonal structure in a suite of abiotic variables (e.g., temperature, dissolved oxygen, pH, inorganic nutrients) and biological attributes (e.g., bacterial production, chlorophyll a concentrations, zooplankton density, catch of fish and jellyfish). Despite this large-scale variation, many metrics nevertheless exhibited associations with local measures of land use, although these associations were often subtle (\u3c 10% of the observed variation) and variable across basins. The general pattern was that abiotic and lower trophic attributes were more sensitive and fish abundance and diversity were less sensitive. These findings suggest that current management practices that assume uniform conditions across Puget Sound and that ignore the cumulative effects of land use actions are unlikely to adequately redress human impacts on pelagic ecosystems