[pp.67-72]

Factors Affecting Distribution of Ulva spp. Blooms in Yatsu Tidal Flat, Japan

Yuichi ISHII, Yoshimasa AMANO and Kazuo TAKI （Ibaraki Kasumigaura Environmental Science Center / Saga University / Chiba Institute of Techology）

Abstract:
The relationships between Ulva spp. bloom and several environmental factors (temperature, tide action, topographical undulation and wind) were examined to better understand the remediation of the tidal flat. The increase in biomass of Ulva spp. in the Yatsu Tidal Flat at the beginning of the summer season lags the increase in air temperature; i.e., in the multiplication period, there is a lag in the time of temperature increase to the time of increased growth. The growth and distribution rate of Ulva spp. is proportional to air temperatures from 15 to 25°C, and this pattern holds in the tidal flat. Ulva spp. accumulates in the tidal flat due to the longer inflow path in the flood tide period and the shorter outflow path in the ebb tide period. The residual ratio of seawater due to the accumulation of Ulva spp. is estimated to be 14%. The extraordinary propagation of Ulva spp. tends to cause a long residual period for the ebb tide period in the tidal flat, and the exposure time between sediment and air becomes shorter. Wind effects—land and sea breezes—do not affect the large distribution of Ulva spp. in the tidal flat for ordinary wind conditions.

Key Word:
Ulva spp., artificial lagoon, temperature, topographical undulation, wind

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