Autoecology and some life history stages of Dinophysis acuta Ehrenberg

A persistent and unusual bloom of Dinophysic acuta Ehrenberg in the RIas Bajas (Northwest Spain) from early July to mid-November 1989, was associated with a diarshetic shellfish poisoning (DSP) outbreak that prevented mussel extraction in some areas from early August to mid-December. Integrated samples (0–5, 5–10 and 10–15 m) were taken once or twice a week at six stations. Maximum numbers of D.acuta (up to 2.3 × 104 intheintegratedsamples)andpercentageofobserveddMdingcells(upto3l%), appearedin August, and formed a maximum in the thermodine. Cell numbers were minimal when upwelling caused a breakdown of stratification. Fligh numbers of D.acuta (up to 1.8 × 104 cells 1–1 appeared again when persistent south winds in late October caused a reversal of the circulation. Thus, the two cell maxima occurred during two distinct hydrographic regimes, but in both cases at temperatures of 15–17°C. Numerous cells with one typical D.acuta valve, but the other valve reduced in size, were seen during the bloom, as well as Dinophysts dens Pavillard cells that might be a life cycle stage of D.acuta. Other observations include double- walled, unwinged forms that are perhaps some kind of cyst, and a hypothetical ‘fertilizing tube’ emerging from the larger cell of a D.acuta/D.dens couplet. It is suggested that the maxima during stratification and during downwelling episodes could correspond to periods with a predominance of in situ growth and physical accumulation, respectively, and that the exceptional meteorological conditions during 1989 provided the optimum scenario for the unusual occurrence of D.acuta.