Abstract
Cell density of the large diatom, Coscinodiscus wailesii causing Nori discoloration, chlorophyll a (Chl a) concentration and nutrient concentrations were determined in Harima-Nada, Seto Inland Sea, Japan from January to December 2004 and from October 2005 to January 2006. The sinking rates of 11 diatom species in natural seawater and six cultured diatom species isolated from same region were also determined. It was estimated that C. wailesii could account for 0-66% of Chl a standing stock in the water column. The sinking rate of C. wailesii cells in natural seawater ranged from 0.75 to 4.19m /day, which were higher than that of other diatom species. Additionally, cultured C. wailesii cells showed the highest sinking rate (2.12m/day) among the cultured diatoms. Due to its high sinking rate, it was suggested that C. wailesii could remove a great amount of nutrient from surface water and transport it to the bottom layer. We believe that C. wailesii plays a great role in the biophilic element cycling of coastal water during low temperature period.
