Dinophysis acuminata and Dinophysis acuta produce lipophilic toxins that cause most shellfish harvesting closures in the Atlantic coastal waters of Europe. Dinophysis often exhibit patchy distributions and sampling with conventional methods may fail to detect them. A 6-month calibration study in 2006, plus an additional sampling in 2010 were carried out in Galicia to compare Dinophysis counts obtained from weekly high vertical resolution bottle samples with depth-integrated hose samples. Counts with these two methods were comparable at some depth-ranges, but hose maxima were over one order of magnitude lower under thin-layer scenarios. Estimates from hose samplers should be used with caution in programmes using a “Dinophysis index”, either to trigger shellfish sampling or to establish precautionary harvesting closures. In general, hose samplers provide reliable information on the occurrence of Dinophysis except under extreme site-specific hydrodynamic conditions. This study adds new information about the heterogeneous, specific vertical distributions of two Dinophysis spp.

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