Co-occurrence of the West European (Gr. III) and North American (Gr. I) ribotypes of Alexandrium tamarense (Dinophyceae) in Shetland, Scotland

An investigation into the diversity of the dinoflagellate Alexandrium was carried out during August 2007 within two fjordic sea lochs in the Shetland Isles, Scotland. The co-occurrence in the water column of the non-toxic West European (W.E. or Gr.III) and the neurotoxic North American (N.A. or Gr.I) ribotypes of A. tamarense was demonstrated using fluorescent insitu hybridisation. A patch of A. tamarense (W. E.) localised at similar to 10 m depth and extending over 6 km was detected in 'Clift Sound' with concentrations locally reaching similar to 1 x 10(4) cells l(-1). A. tamarense (N.A.) was also observed there but despite the presence of toxins in net haul samples collected locally, concentrations were low and near limits of detection. Alexandrium concentrations were similar to 1.5 x 10(3) cells l(-1) in 'Vaila Sound', where both W. E. and N.A. ribotypes were detected with equal relative abundances in some samples. Given the patchiness of A. tamarense populations and their possible organisation in thin layer structures, better vertical resolution through fine-scales ampling will be necessary for population dynamic studies. Implications for the shell fish industry are substantial since harmful micro algae patches may not be detected during routine monitoring. Moreover, the co-occurrence of morphologically indistinct toxic and non-toxic ribotypes will necessitate implementing molecular methods for their discrimination. (C) 2010 Elsevier GmbH. All rights reserved.