Phylogeny of a new ichthyotoxic dictyochophyte forming blooms in the Skagerrak

Summary

Since 1998 a heterokont flagellate, initially identified as Chattonella aff. verruculosa, has formed recurrent extensive blooms in the North Sea and Skagerrak causing mortality in farmed salmon. Strains were isolated from a 2001 bloom off the south coast of Norway and compared with a �Chattonella verruculosa� strain from Japan. The cells in Norwegian strains are oblong to round with numerous chloroplasts and mycocyst-like organelles. The complete SSU and partial LSU rRNA gene sequences from strains from Norway and Japan were similar, but not identical, and differed clearly from rDNA sequences of other Raphidophytes. Phylogenetic trees were constructed and their relationships to other heterokontophytes determined. C. aff. verruculosa and the Japanese �C. verruculosa� appeared in a clade with members of Dictyochophyceae. Ultrastructure (e.g. the structure of flagella and flagellar apparatus, position of nucleus), morphology and pigment data (chlorophylls a, c1, c2, c3, fucoxanthin, diadinoxanthin and 19�butanoyloxyfucoxanthin) support this affinity. A new name and classification will be proposed.