Survival and recovery of resting spores and resting cells of the marine planktonic diatom Chaetoceros pseudocurvisetus under fluctuating nitrate conditions

Of the two resting life-forms of the planktonic diatom Chaetoceros pseudocurvisetus Mangin formed during periods of nitrate depletion, resting spores survived at least 1 month after spore formation at 24 degrees C, while resting cells survived only for about 10 d at the same temperature. Under nitrogen limitation, resting cells exhibited higher specific death rates than resting spores at temperatures ranging from 5 to 30 degrees C. After nitrogen replenishment, resting spores required a certain lag period of about 1 d to initiate vegetative growth at levels of nitrate supply from 0.5 to 20 mu M, while resting cells initiated vegetative growth almost immediately. Resting spores exhibited an intracellular accumulation of the supplied nitrate during germination and initial vegetative growth. The resting cells, however, exhibited more active vegetative growth, closely coupled with the uptake of the supplied nitrate. The resting spores and resting cells appear to play different roles in the maintenance of populations under nutrient fluctuations depending on the interval length between nutrient fluxes in natural waters.