NOTES ON A MESODINIUM-RUBRUM RED TIDE IN SAN-FRANCISCO BAY (CALIFORNIA, USA)

Discrete red patches of water were observed in South San Francisco Bay (USA) on 30 April 1993, and examination of live samples showed that t his red tide was caused by surface accumulations of the pigmented cili ate Mesodinium rubrum. Vertical profiles showed strong salinity and te mperature stratification in the upper 5 m, peak chlorophyll fluorescen ce in the upper meter, and differences in the small-scale density stru cture and fluorescence distribution among red patches. Events precedin g this Mesodinium red tide included: (i) heavy precipitation and run-o ff, allowing for strong salinity stratification; (ii) a spring diatom bloom where the chlorophyll a concentration reached 50 mg m(-3); (ii) depletions of dissolved inorganic N and Si in the photic zone; and (iv ) several days of rapid warming and stabilization of the upper surface layer. These conditions may be general prerequisites for M rubrum blo oms in temperate estuaries.