Heterotrophic dinoflagellate fecal pellet production: grazing of large, chain-forming diatoms during upwelling events in Monterey Bay, California

An athecate phagotrophic dinoflagellate (Gyrodinium sp.) ingests chain-forming diatoms that are abundant during upwelling events in Monterey Bay, CA, USA, and contiguous waters. The chains are digested and egested with a peritrophic membrane covering the fecal pellet, consistent with earlier reports from high productivity environments. The maximum abundance of the dinoflagellate during more than a decade of monitoring was 4000 cells l -1 . Its primary prey comprised chains of centric diatoms such as Chaetoceros spp. or Skeletonema spp., although Pseudo-nitzschia spp. were also observed in the dinoflagellate's fecal pellets. Maximum grazing by this dinoflagellate represented 10% of the total phytoplankton biomass. Our observations suggest a lesser role of large heterotrophic dinoflagellates in the ecology of central California waters compared to other regions.