A resurgence of dinoflagellates, which can cause harmful algal blooms, may be in the cards for some bays along the U.S. West Coast. Scientists at UC Santa Cruz have been monitoring phytoplankton weekly at the town’s Municipal Wharf since 2002. In 2018, Alexis Fischer, then a postdoctoral fellow at UC Santa Cruz, augmented these observations with an Imaging FlowCytobot (IFCB)
that photographed wharf phytoplankton hourly. She also developed a machine learning classification algorithm to automate identification of the organisms. In 2004-2007 and 2017-2018, the scientists noticed that diatoms, typically dominant, were getting upstaged by dinoflagellates. To get to the root of this role switch, Fischer examined local and regional environmental patterns. She now reports in Limnology and Oceanography
that both anomalies were accompanied by unusual local winds and a negative swing in the North Pacific Gyre Oscillation, which reduces upwelling and results in warmer, stratified water. “I would see the transition from upwelling to relaxation in Monterey Bay through water temperatures and wind and current pattern data, and then a couple days later see dinoflagellates bloom at the wharf through IFCB data,” says Fischer. She suspects that upwelling aggregated strong dinoflagellate swimmers such as Akashiwo sanguinea
at thermal ocean fronts. When upwelling relaxed, a shift in water circulation transported these dinoflagellates close to the northeastern shore of Monterey Bay. Local winds from the south and west kept the dinoflagellates marinating in balmy water near the wharf, where they bloomed. Climate warming is expected to cause the NPGO to vary even more strongly, suggesting that “ages of dinoflagellates” could become more common in Monterey Bay and similar places, such as San Luis Obispo Bay. Unfortunately, the researchers have had to temporarily suspend the long-term phytoplankton monitoring that made this finding possible due to coronavirus restrictions imposed this spring.