Detection of Prorocentrum shikokuense in the Mediterranean Sea and evidence that P. dentatum, P. obtusidens and P. shikokuense are three different species (Prorocentrales, Dinophyceae)

Abstract

A dinoflagellate identified as Prorocentrum dentatum, P. shikokuense or P. donghaiense is responsible of massive harmful events. Blooms of a species identified as P. shikokuense have been recently reported in the Mediterranean Sea, and an exotic origin, tentatively in-troduced by ballast waters from Asia, has been hypothesized. The molecular data based on the small-, large subunit, and internal transcriber spacers ribosomal RNA gene (SSU-, LSU-, ITS rRNA) sequences confirmed P. shikokuense in the Mediterranean Sea. The Mediterranean ribotype is identical to a subtropical North Atlantic ribotype, and with slight divergence from the numerous sequences from the Pacific Ocean. To revisit the relationship between P. shikokuense (=P. donghaiense) and P. obtusidens, we provide the first micrographs of P. den-tatum and P. obtusidens, the latter collected from the type locality. Our observations indicate that P. dentatum, P. obtusidens, and P. shi-kokuense are three different species. Their diagnostic morphological characters are: Prorocentrum dentatum is 44–60 µm long, leaf-shaped, pointed and central posterior end, conspicuous anterior shoulder; P. obtusidens is 33–41 µm long, irregular parallelepiped, almost parallel valve margins, eccentric and pointed posterior end, moderate anterior shoulder; and P. shikokuense is <25 µm long, sunflower seed-shaped, round and centric posterior end, inconspicuous anterior shoulder.