SEED BANK OF COASTAL PLANKTONIC DIATOMS IN BOTTOM SEDIMENTS OF HIROSHIMA BAY, SETO INLAND SEA, JAPAN

Abundance and temporal distribution of viable (able to germinate) rest ing stage cells of planktonic diatoms in bottom sediments have been in vestigated almost monthly during 1989 to 1992 in Hiroshima Bay, wester n part of Seto Inland Sea, Japan. The abundance of viable resting stag es in bottom sediments was enumerated with the extinction dilution met hod (most probable number method, MPN). In bottom sediments of Hiroshi ma Bay, dominantly distributed species and/or genera of the diatom res ting stages were Skeletonema costatum, Chaetoceros spp. and Thalassios ira spp. Viable resting stages of these diatoms were densely distribut ed on the orders of 10(3) to 10(6) (MPN g(-1) wet sediments), and pers isted in bottom sediments throughout the investigation period. Convers ely, vegetative cells of these diatoms fluctuated remarkably in the wa ter column and disappeared sporadically. Survival of the resting stage s in a collected sediment sample was also determined with the MPN meth od, at different storage temperatures (5, 10, 15, 20, 25 degrees C). T he survival test demonstrated that the diatom resting stages could sur vive in the dark for several months or years in sediments. Resting sta ges survived longer at the lower storage temperature, and the order of longevity was consistent within three diatoms (Chaetoceros spp. > Tha lassiosira spp. > S. costatum) at each storage temperature. The presen t study suggests that these diatom resting stages in the coastal botto m sediments could serve as a ''seed bank'', analogous to those of terr estrial plants. The seed bank would ensure the survival of diatoms wit hin highly fluctuating coastal environments, while it would also be th e source of sporadic and autochthonous diatom blooms in coastal waters .