抄録
In 2008, the European invasive ascidian Ascidiella aspersa (Müller, 1776) was reported for the first time in Funka Bay, Hokkaido, Japan, and it has since caused serious damage to the cultured scallop industry in the bay. The distribution and abundance of A. aspersa were investigated in Hokkaido. Between 2010 and 2013, ascidians suspected to be A. aspersa were collected from 20 sites in Hokkaido and identified using internal morphological and follicle cell characteristics. In addition, the abundance of A. aspersa attached to cultured scallops was investigated at 10 stations near Funka Bay in October 2012 and 2013. A. aspersa was found on the Pacific coast, Sea of Japan coast, and in Tsugaru Strait, showing that it was widely distributed in Hokkaido in 2010. A. aspersa was found at all the stations near Funka Bay, and the number of A. aspersa on scallops was much greater inside the bay than outside of the bay. A. aspersa is known to occur in low-energy environments like estuaries, harbors, and semi-closed embayments. Its range expansion should be monitored and measures should be considered to limit its expansion.
