Notes on a Mesodinium rubrum red tide in San Francisco Bay (California, USA)

Discrete red patches of water were observed in South San FranciscoBay (USA) on 30 April 1993, and examination of live samplesshowed that this red tide was caused by surface accumulationsof the pigmented ciliate Mesodinium rubrum. Vertical profilesshowed strong salinity and temperature stratification in theupper 5 m, peak chlorophyll fluorescence in the upper meter,and differences in the small-scale density structure and fluorescencedistribution among red patches. Events preceding this Mesodiniumred tide included: (i) heavy precipitation and run-off, allowingfor strong salinity stratification; (ii) a spring diatom bloomwhere the chlorophyll a concentration reached 50 mg m^–3;(ii) depletions of dissolved inorganic N and Si in the photiczone; and (iv) several days of rapid warming and stabilizationof the upper surface layer. These conditions may be generalprerequisites for M.rubrum blooms in temperate estuaries. ¹Present address: Station Marine d'Endoume, Centre d'Oceanologiede Marseille, rue Batterie des Lions, 13007 Marseille, France