Monterey Bay is the largest open embayment along the U.S. west coast and is subject to intense autumn dinoflagellate blooms, many of which are harmful. During 2004–2007 these blooms were so dominant that this period was called the “age of dinoflagellates”. From mid-2017 through 2018, after a decade of absence, a diversity of dinoflagellates returned to dominate the phytoplankton biomass. To quantify bloom development at high temporal resolution, an Imaging FlowCytobot was deployed within the upwelling shadow of the northern bay at Santa Cruz Municipal Wharf (SCW) and a machine learning image classifier was developed to identify the local phytoplankton assemblage. In 2018, dinoflagellates comprised 57% of the annual phytoplankton-specific carbon biomass, and 62% from January to May. This is unusual given that Monterey Bay is typically diatom-dominated during spring upwelling. 2018 was characterized by strong upwelling interspersed with frequent relaxation, which contributed to unusually retentive winds and currents. The resulting warm and stratified northern bay was frequently resupplied with upwelled nutrients and frontal aggregations of dinoflagellates. Analysis of an 18-year weekly SCW timeseries suggests that both “age of dinoflagellate” periods were linked to a negative NPGO and its associated effects of increased sea surface temperatures and stratification. As the climate continues to warm, periods of increased dinoflagellate dominance in the California Current System may become more common. This high resolution IFCB timeseries combined with ocean robotics from MBARI give us the potential to predict blooms in the northern bay in the future. This retreat strives to bring together a number of collaborators to generate ideas to write an NSF proposal doing just that.

Approved