Dinophysis acuminata, D. acuta, and D.caudata co-occur during early autumn DSP outbreaks in the Galician Rías Bajas at the end of the upwelling season, and the contribution of these species to shellfish toxicity needed to be established. HPLC ˆ FD analyzes of single cell isolates of these species during different events confirmed that D. acuta , with an OA:DTX-2 ratio of 3:2, is the source of DTX-2 toxin detected in Galician mussels, and that either D. acuta or D. acuminata can be the main contributor to the autumn toxic outbreaks. Preliminary results suggest that D. caudata has trace amounts of OA (<1 pg · cel ˆ1). The present results confirm the large variability in toxin content in D. acuta and D. acuminata during different seasonal outbreaks, or even during the same outbreak in natural populations kept in the laboratory. The risk for human health of using a „Dinophysis index‰ as substitute information for the standard mouse bioassay in the early detection of diarrhetic shellfish toxicity is discussed.