Production of diarrhetic shellfish poisoning toxins and pectenotoxins at depths within and below the euphotic zone.

During a 10 day survey in the CelticSea near the Irish South-West coast (July 2007), Dinophysis acuta was observed in large numbers. The deployment of a profiler allowed for the identification of a D. acuta thin layer that reached 1910 cells/L. The aim of the study was to investigate if the bloom that occurred in low light environment was viable, dividing, actively producing toxins and if the toxin profile changed over a short term period. Several large concentrates of phytoplankton samples were obtained over a 14 h period, from evening to morning, by pumping Dinophysis from specific depths. In addition, D. acuta was collected in complete darkness at 81 m depth by concentrating 120 L of water. The cells were extracted and their toxin profiles were established by liquid chromatography - mass spectrometry (LC-MS). Passive samplers were deployed in a nearby location for 6 days at 30, 50, 70 and 110 m depth, and the toxin profiles were determined by LC-MS as above. The toxin profiles obtained in phytoplankton samples and in the SPATT were compared and correlated well. Sample concentrates and SPATT results suggested that toxic D. acuta occurred and produced similar toxin profiles at all water depths, including below the euphotic zone.

Genetic diversity and molecular detection of three toxic dinoflagellate genera (Alexandrium, Dinophysis, and Karenia) from French coasts.

The objectives of this study were 1) to study the genetic diversity of the Alexandrium, Dinophysis and Karenia genera along the French coasts in order to design probes targeting specific DNA regions, and 2) to apply PCR-based detection to detect these three toxic dinoflagellate genera in natural samples. Genetic diversity of these toxic taxa was first studied from either cultures or cells isolated from Lugol-fixed field samples. By this way, partial sequences of the large ribosomal subunit (LSU rDNA) including the variable domains D1 and D2 of A. minutum, Alexandrium species inside the tamarensis complex, the D. acuminata complex and K. mikimotoi were obtained. Next, specific primers were designed for a selection of toxic algae and used during semi-nested PCR detection. This method was tested over a 3-month period on water samples from the Bay of Concarneau (Brittany, France) and on sediment from the Antifer harbor (The English Channel, France). Specificity and sensitivity of this molecular detection were evaluated using the occurrence of target taxa reported by the IFREMER (Institut Français de Recherche pour l'Exploitation de la Mer) monitoring network based on conventional microscopic examination. This work presents the first results obtained on the biogeographical distribution of genotypes of these three toxic genera along the French coasts.