Abstract

In 2005, a bloom of the Diarrhoetic Shellfish Poisoning (DSP) causative agent Dinophysis acuta Ehrenberg in the Galician Rías Baixas (NW Spain) started in early August and reached maximum densities (up to 2 × 10 4 cell l-1) in mid November. A cell cycle study was carried out over a 22 h period on 9 and 10 November to describe the physiological status and the short-term variability in cell toxin quota of D. acuta at the time of the annual maximum of lipophilic toxins in shellfish. At that time, the population of D. acuta showed an extremely low division rate (μ = 0.03 d-1), a high frequency of dead cells (up to 15%) and cells with starch granules (up to 93%), and no evidence of recent mixotrophic behaviour. Still, the cells, which did not perform vertical migration, aggregated around salinity-driven density discontinuities in the top 5 m and had a high cell toxin quota (determined by liquid chromatography-mass spectrometry) for this species. A 3.5-fold difference was found between maximum (during the night) and minimum values of cell toxin quota. Okadaic acid (OA) was the predominant toxin and changes in cell quota of different toxins showed different daily patterns in the content of okadaiates and pectenotoxins; thus, the toxin profile is influenced by the time of sampling. Dissolved toxins (adsorbed by resins in passive samplers from 8 to 14 November) also reached annual maxima and reflected the vertical distribution of D. acuta cells. These results emphasize the need to parameterize physiological conditions and behaviour of Dinophysis populations during different phases of the population growth and hydrodynamic scenarios. © Inter-Research 2008.