Temperature modulates metabolic rates and cell viability in complex ways. However, it is typically implemented in models of microbial dynamics as a one-size-fits-all regulator on metabolic rates alone, and with no consideration for thermal-damage induced mortality. Using agent-based modeling (ABM) in a simulated ocean with temperature variability on diel and longer time scales, we explore the patterns of metabolic rate and mortality rate regulation under different fluctuating temperature regimes. ABM allows us to explicitly record the thermal history of each cell, enabling the parameterization of accumulated thermal damage. Since microbial populations are often composed of multiple coexisting subpopulations with distinct physiological properties, that accumulated damage has age and taxonomic structure and is not uniformly distributed in the population. Results from ABM simulations of heterogeneous populations with differing optimal growth temperatures showed qualitatively different population dynamics than those computed from the bulk average. Furthermore, using a reanalysis of global temperature variability, we find that thermal mortality has the potential to reshape community composition, especially during episodic 'marine heatwave' events.
 

phytoplankton,accumulated thermal damage