Taxonomic revision of<i>Chattonella antiqua, C. marina</i>and<i>C. ovata</i>(Raphidophyceae) based on their morphological characteristics and genetic diversity

Abstract

Demura M., Noël M.-H., Kasai F., Watanabe M.M. and Kawachi M. 2009. Taxonomic revision of Chattonella antiqua, C. marina and C. ovata (Raphidophyceae) based on their morphological characteristics and genetic diversity. Phycologia 48: 518–535. DOI: 10.2216/08-98.1.Three raphidophyte species, Chattonella antiqua, C. marina and C. ovata, are red tide–forming harmful phytoplankton species, causing mass mortality at fish farms. These species were originally distinguished from each other solely based on their morphological characters. Recent genetic diversity analyses showed that the three species were extremely similar. It was therefore necessary to re-examine these three species to determine if they were independent single species. We compared 104 strains of the three species using morphological characters, nuclear ITS rDNA regions, the chloroplast rbcL gene, the mitochondrion COI gene and selected microsatellite regions. The morphological characters for the three species formed a continuum of variation instead of clearly defined limits. Compared with other selected heterokontophytes, their genetic divergence in the analyzed three regions was found to be at the intraspecies level. Microsatellite markers distinguished each of the 104 strains, but the strains apparently formed a single geographical population. Based on the morphological characters and the phylogenetic analyses, three groups, corresponding to each of the three Chattonella species, were roughly recognized. Nevertheless, this three-group distribution was insufficient to justify their distinction at the species rank. We therefore proposed a taxonomic revision with C. antiqua and C. ovata reduced to varieties of C. marina, this latter having name priority. We proposed a new status: C. marina var. antiqua (Hada) Demura & Kawachi and C. marina var. ovata (Y. Hara & Chihara) Demura & Kawachi.