Presenter: Cara Schiksnis (University of Southern California)

Description:
It is well-accepted that increasing sea surface temperatures driven by anthropogenic activity will alter marine primary productivity, but within the common setting of the ocean’s nutrient limited regions, the effects of warming on phytoplankton growth and function are not well understood. Prochlorococcus is the world’s most abundant primary producer and contributes significantly to carbon fixation and biogeochemical cycling in the ocean, as it frequently dominates photoautotrophs in the oligotrophic regions. Multi-stressor studies highlight how complex interactions can occur in ways not predictable when applying these stressors individually. Few studies have indicated a potential for interactive effects between warming and iron limitation in some marine cyanobacteria, but this response has not been defined for Prochlorococcus and under other common types of nutrient limitation. Prochlorococcus strain MED4 was isolated from the Mediterranean Sea, a climate change hotspot where warming will occur rapidly while chronically low concentrations of the essential macronutrient phosphorous (P) limit phytoplankton growth. To enhance our understanding of the effects of multiple environmental changes on MED4, we acclimated unialgal cultures to a range of P concentrations (from limiting to replete) at 3 temperatures (18°C, 27°C, 30°C). Preliminary results to be discussed include how MED4 growth rates and properties such as cellular stoichiometry and nutrient growth kinetics are impacted by these dual climate change stressors. We found that warming beyond the thermal optimum decreased the half saturation constant and increased the P growth affinity, indicating that MED4 growth may benefit from climate warming in the P limited Mediterranean Sea. This study continues to highlight the importance of incorporating multiple stressors for understanding the ways in which complex climate change interactions affect biology and biogeochemical cycling so that we can better predict a more realistic picture of the future ocean.