Seasonal variability of lipophilic toxins during a Dinophysis acuta bloom in Western Iberia: Differences between picked cells and plankton concentrates

This work describes and compares the seasonal variability of toxin profiles and content, estimated by LC-MS analyses, in picked cell of Dinophysis acuta Ehrenberg, in plankton concentrates rich in this species, and in extracellular lipophilic toxins collected by adsorbent resins during weekly sampling in a Galician ria (Western Iberia) from October 2005 to January 2006. Picked cells of D. acuta-which exhibited a fairly stable OA:DTX2 ratio, close to 3:2, but a variable okadaates:PTX2 ratio-showed a 9-fold variation in cell toxin quota, which was partly related to cellular volume, with maximum values (19 pg cell(-1)) observed during the exponential decline of the population. Large differences in toxin profiles and content were observed between picked cells and plankton concentrates (up to 73 pg cell(-1) in the latter), that were most conspicuous after the bloom decline. The toxin profile of picked cells was more similar to that observed in the adsorbent resins than to the profiles of plankton concentrates. Their continued detection several weeks after the disappearance of Dinophysis spp. indicates that these toxins may take a long time to be degraded. It is concluded that analyses of picked-cells are essential to determine the contribution of each species of Dinophysis to a toxic outbreak. Estimates of cellular toxin content from plankton concentrates can lead to considerable overestimates after Dinophysis blooms decay due to extracellular toxins that persist in the water column, possibly bound to organic aggregates and detritus, and are retained (>0.22 mu m) in the filters. (C) 2009 Elsevier B.V. All rights reserved.