Viability of phytoplankton resting stages in the sediments of a coastal Swedish fjord

Viable diatom and dinoflagellate resting stages were recovered from sediments in Koljo Fjord on the west coast of Sweden. To determine the maximum survival time of buried resting stages, samples from sediment depths down to 50 cm were incubated at temperatures of 3, 10 and 18 degreesC. Sediment cores were dated by Pb-210 and the age of samples containing viable resting stages was determined using the constant rate of supply model. Dilution cultures of surface sediments allowed semiquantitative estimates of the potential seed bank. Dinoflagellate cysts from species such as Diplopsalis sp.. Gymnodinium nolleri, Oblea rotunda and Protoceratium reticulatum were viable clown to 15 cm depth, or 37 years old. Spores and resting cells of the diatoms Chaetoceros spp., Detonzda confervacea and Skeletonema costatum were viable to over 40 cm depth. and may have been buried for Man. decades. The seed bank of living resting stages in surficial sediments was found to be rich (c. 57000 diatom resting stages g(-1) wet weight and c. 200 dinoflagellate cysts g(-1) wet weight), and the percentage of viable resting stages was higher for spore- and cyst-forming species. The oxygen-deficient sediments in Koljo Fjord appear to be a natural conservator of cell viability, a condition not easily simulated in laboratory studies. These results are ecologically important since spores and cysts are a repository of genetic material able to repopulate waters if resuspended and exposed to suitable light, temperature and nutrients.