1Niigata Prefectural Fisheries and Marine Research Institute, Nishi-ku, Niigata 950-2171, 2Nagasaki University, Bunkyo-cho, Nagasaki 851-2213, 3Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Hatsukaichi, Hiroshima 739-0452, 4Seikai National Fisheries Research Institute, Fisheries Research Agency, Taira-cho, Nagasaki 851-2213, Japan
Lake Kamo is a small brackish lagoon located in Sado Island, Niigata, Japan (38°06′N, 138°44′E) and is famous for cultivation of the Pacific oyster Crassostrea gigas. In autumn 2009, a dinoflagellate Heterocapsa circularisquama formed a bloom in this lake, causing mass mortality of a considerable proportion of the cultured Pacific oysters and fisheries damage estimated to be 190 million Japanese yen. Although the origin or cause of entry of the H. circularisquama population into Lake Kamo is unknown, heavy stirring due to a large typhoon is considered to be a possible trigger of its blooming. This was the first attack by H. circularisquama in this lake; prior to this bloom, the northern limit of the distribution range of H. circularisquama had been Obama Bay, Fukui, Japan (35°50′N, 135°72′E). A H. circularisquama bloom recurred in Lake Kamo in the summer of 2010, although it did not cause considerable damage to cultured oysters. This phenomenon is considered to be a typical case of the northward expansion of harmful algae in the Northern Hemisphere.