Evaluating the Vulnerability of Oregon Seagrass Beds to Eutrophication (2016-18)

Fiona Tomas Nash
Department of Fisheries and Wildlife
Oregon State University
101 Nash Hall
Corvallis, OR 97331
Phone: 541-737-4531

Co-PIs: Steve Rumrill, Oregon Department of Fish and Wildlife (ODFW); James Kaldy, U.S. EPA; Anthony D’Andrea, ODFW; Bree Yednock, South Slough National Estuarine Research Reserve (NERR); Renee O’Neill, OSU; Joy Tally, South Slough NERR

Oregon estuaries exhibit major differences in nutrient levels and dynamics compared to estuaries elsewhere, as they not only receive nutrients through watershed contributions (mainly during the wet season from November to March), but are also strongly influenced by oceanic upwelling (during the dry season). These alternative nutrient delivery systems create a conundrum for managers and policy makers because the natural levels of nutrient loading in some Oregon estuaries can be the same or greater than loading in estuaries that are considered eutrophic (i.e., overabundance of plant life due to high nutrient concentrations) elsewhere in the US. Current models of eelgrass response and vulnerability to eutrophication are unlikely to be suitable for making predictions about the healthy functioning of eelgrass beds in Oregon or for establishing conservation priorities and regulations.

The presence and diversity of small invertebrate herbivores collectively referred to as mesograzers are critical in buffering the negative effect of eutrophication on seagrasses. However, mesograzer communities of Oregon eelgrass beds have not been well characterized, which precludes our capacity to predict the role they may have in controlling epiphytic growth and thus buffering negative eutrophication impacts on seagrass. In addition, Oregon estuaries now harbor the non-native seagrass Zostera japonica, but the role of nutrient availability on limiting or favoring Z. japonica, or the potential effects nutrients may have in determining competitive interactions between native and introduced seagrass remain unexplored.

Dr. Tomas Nash and her research team hypothesizes that the severity and type of impacts from eutrophication on Oregon seagrass beds will depend not only on the levels of nutrient loading, but also on the type of estuary, regional drivers (e.g. upwelling), and the local mesograzer communities. Thus, predicting the vulnerability of Oregon seagrass beds to eutrophication requires a multi-estuary, coast-wide evaluation that takes into account nutrient regimes and the mesograzer communities of each particular estuary. The project will fill important information gaps for agencies and coastal communities that currently limit the ability to assess and predict the risk of eutrophication to Oregon seagrass beds.

Strategic Plan Focus Areas: Healthy Coastal Ecosystems,Sustainable Fisheries and Aquaculture

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