Connectivity in Coos Bay, OR: do changes in physical dynamics lead to changes in eelgrass habitat?

The Coos Bay Estuary, in southern Oregon, is a tidally-driven estuary with significant spring/neap variability and seasonal river discharge input. During 2014-2016 warm anomalies related to the “Blob” and ENSO warm-phase events affected the estuary by increasing water temperatures, changing the seasonal upwelling and decreasing precipitation. In 2015, records from the South Slough National Estuarine Research Reserve (SSNERR), located in the shallow southern arm of the main estuary, showed a decline in eelgrass abundance. However, at the same time there were no significant changes in eelgrass abundance in the main estuary. Here we focus on the connectivity of the main portion of the estuary with South Slough using both long-term observational data sets and particle-tracking experiments based on realistic numerical simulations to analyze the effects of river discharge and winds on the estuarine transport . We examine whether the observed interannual changes in meteorological and oceanographic conditions could affect the connectivity between the main estuary and South Slough, thus leading to distinct trends in ecosystem health. Results suggest that shifts in tidal phasing may significantly influence the residence time of certain water masses within South Slough. Our study has implications for the ecological functioning of sub-estuaries where increased residence times of water masses can stress the functioning of marine ecosystems.