Abstract
We present the first report to our knowledge of an alien ascidian Molgula manhattensis (DeKay, 1843) from Akkeshi-ko Estuary in Hokkaido. M. manhattensis was identified through molecular analysis using about 840 bp of nuclear 18S rRNA and about 546 bp of mitochondrial cytochrome C oxidase subunit 1 (mt-CO1) genes, and by evaluating its morphological and biological characteristics. The 18S rRNA gene analysis and evaluations of the morphological and biological features are considered more preferable than mt-CO1 gene analysis for the identification of M. manhattensis, because the mt-CO1 genes of M. manhattensis and the congener M. provisionalis in the GenBank at National Center for Biotechnology Information (NCBI) are identical. Akkeshi-ko Estuary is a known production area of cultured oyster (Crassostrea gigas); the introduction of M. manhattensis possibly occurred during oyster cultch transfer from Honshu. Our findings show that the distribution of M. manhattensis has expanded over a wide range in Japan (from Kyushu to Hokkaido) during the 40 years since it was first reported in Japan.
