The role of environmental factors in the population dynamics of the harmful diatom Asteroplanus karianus in the Ariake Sea, off Saga Prefecture, Japan

Saga Prefectural Ariake Fisheries Research and Development Center, Ogi, Saga 849-0313, Japan

  Asteroplanus karianus is a harmful diatom and a causative organism in the bleaching of cultured nori (Pyropia). The relationship between the population dynamics of A. karianus and environmental factors was investigated in the Ariake Sea, off Saga Prefecture, Japan. Phytoplankton composition and relevant environmental variables were recorded from December 2007 to March 2012. In addition, the growth and germination of A. karianus under high water temperature and low water temperature conditions were studied in the laboratory. The field study indicated that A. karianus caused red tides only in winter. Nonetheless, laboratory studies indicated that the growth rate of A. karianus was higher under high water temperature conditions than low water temperature conditions. Conversely, the results suggested that the time required for germination of resting stage cells of A. karianus, in bottom sediment was shorter under low water temperature conditions.

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