Permalink : http://hdl.handle.net/2115/58038

JaLCDOI : 10.14943/bull.fish.65.1.31

KEYWORDS : Diatom;Chaetoceros;Thalassiosira;Skeletonema;Resting stage cells;Resting cells;Resting spores;Harima-Nada;Osaka Bay;Bottom sediment

Spatial distributions of viable diatom resting stage cells (DRSC) in bottom sediments (top 3-cm depth) of Harima-Nada and Osaka Bay, eastern Seto 1nland Sea, were investigated with the extinction dilution method (Most Probable Number (MPN) method) based on sediment incubation.　The sampling cruise was carried out from June 13 to 16 in 2000.　The dominant groups of DRSCs were composed of the species of the genera Chaetoceros, Thalassiosira and Skeletonema in sediment samples that ranged from ND (not detectable) to 1.3×105 MPN cm-3 (mean 1.5×104), from ND to 1.7×105 MPN cm-3 (mean 2.4×104), and from ND to 4.9×104 MPN cm-3 wet sediment (mean 9.2×103), respectively.　The densities of DRSCs of other dominant species were also enumerated on such as Skeletonema tropicum, Leptocylindrus danicus, Leptocylindrus minimus, Asterionellopsis glacialis, Thalassionema nitzschioides, Bacteriastrum hyalimum, Odontella longicruris and Stephanopyxis palmeriana.　The total number of DRSCs reached a maximum value of 2.1×105 MPN cm-3 wet sediment (mean 5.1×104).　The DRSCs in bottom sediments generally distributed more abundantly at the coasts of Harima-Nada where more frequent diatom blooms have occurred than offshore areas showing lower densities of DRSCs.　The most dominant diatom genus was Thalassiosira, followed by Chaetoceros and Skeletonema.　The previous investigation in 1993 revealed the dominance of Skeletonema resting cells in bottom sediments in the northern coast of Harima-Nada, but Skeletonema resting cells were not abundant in 2000, suggesting a change of water quality conditions from eutrophication to oligotrophication to significant degree.