• phytoplankton;
  • dinoflagellates;
  • red tide

[1] Novel remote sensing methods and in situ observations reveal that intense dinoflagellate blooms occur frequently in Monterey Bay, California. Blooms can contain surface chlorophyll concentrations exceeding 500 μg l−1 and occupy ∼5 to 80 km2. They occur primarily during August through November and can persist for > 1 month. Maximum bloom frequency and mean intensity are in a shallow (< 25 m depth) area of the northeastern bay, in coincidence with the warmest surface water, low wind stress, and retentive circulation. These conditions favor dinoflagellates, which can vertically migrate to acquire nutrients in the thermocline and aggregate as "red tide" near the surface. Bloom incubation areas, also indicated in other coastal upwelling systems, may disproportionately influence regional bloom ecology.