Temporal distribution of the potentially toxic diatom Pseudonitzschia australis at a coastal site in Southern California

Species of the genus Pseudonitzschia have been implicated in outbreaks of domoic acid (DA) toxicity off the coasts of North America. This led us to look at the historical (1930-1939, 1967, 1983, 1991-1993) occurrence and abundance of these species off the Scripps Institution of Oceanography pier, Southern California, USA, with special emphasis on l? australis Frenguelli for which we have the most complete data. The organism occurs sporadically in high numbers (10' to 106 cells I-') between February and August but no major toxic episodes have been reported. The periods of high abundance were associated with intrusion of cool, high-nutrient waters probably related to upwelling events. To date, there have been no major DA outbreaks in the Southern California Bight.