The marine diatom Thalassiosira pseudonana is more resilient in an acidified ocean

Diatoms are critical for many aquatic food webs, accounting for ~40 percent of marine primary production. Although species composition and abundance of diatoms are known to fluctuate with environmental changes, their fate in acidified oceans of the future is uncertain. Here, we report results from a laboratory stress test designed to quantify the resilience of Thalassiosira pseudonana in mid-20th century (300 ppm CO2) and future (1,000 ppm CO2) conditions. We probed the ability of this model diatom to recover from incrementally higher amounts of stress (low dose UV-AB radiation) and re-initiate growth in day-night cycles, limited by nitrogen (N). While all cultures were eventually unable to recover from stress and resume growth, those growing at 300 ppm CO2 showed increased sensitivity and succumbed significantly earlier compared to cultures growing at 1,000 ppm CO2. We show that in both CO2 conditions as they approached the point of no recovery, the diatom cultures suffered a general “loss of relational resilience”, i.e., they were unable to adopt physiological states that were matched to N-availability and phase of the diurnal cycle. This discordance between internal cellular state and the external environment appears to be an early warning signal for a diatom culture that is approaching collapse. Furthermore, diatom cultures on the brink of collapse took longer to recover and displayed variable photosynthetic efficiencies over growth and across replicates. Our findings predict that the reduced requirement for concentrating carbon for photosynthesis in elevated CO2 (1,000 ppm) conditions will free up cellular resources for stress management making T. pseudonana more resilient in an acidified ocean.