Survival in the dark: strategies adopted by <i>Tetraselmis indica</i> (Chlorodendrophyceae, Chlorophyta)

The adaptive strategy of <i>Tetraselmis indica</i> to survive darkness was evaluated over a period of 182 days. Resting cells formation and reduction in catabolic activity facilitated dark survival and their rejuvenation. The occurrence of thick-walled cells (type 1) and thin-walled cells with the condensed chloroplast (type 2) in light-dark and dark conditions respectively indicated differential resting cell formation. The dissolved organic carbon remained nearly constant throughout the dark period signifying <i>T. indica</i> did not favour heterotrophy. Upon re-illumination of dark-adapted cells, the lag phase lengthened from 2 to 28 days when darkness period increased from 8 to 182 days, respectively. However, this negative influence on growth was compensated by an increase in growth rate from 0.35 to 0.95 d⁻¹. This resurgence capability of <i>T. indica</i> after six months of dark exposure and distinctive resting cell formation indicate a differential population sustenance mechanism. Further elucidation of dark adaptability and survival strategies in <i>T. indica</i> may have significance in ecological and evolutionary processes.