Field surveys were carried out to clarify the effect of geographical features and currents on the distribution of green-tide forming seaweed, Ulva ohnoi at the artificial tidal flat of Hannan Second District in 2011-2012. Thalli of Ulva accumulated on the northern part of the flat due to the tidal current on the flood tide. In contrast, they did not move from the north to the south of the flat because of the slow current on the ebb tide. Wind-driven currents also acted as a factor for the accumulation of Ulva on the flat. The water route was thought to play an important role on the accumulation or dispersion of Ulva at the artificial tidal flat of Hannan Second District.
