Fitted Fv/Fm temperature response curves: applying lessons from plant ecophysiology to acute thermal stress experiments in coral holobionts.

Abstract

Maximum photochemical efficiency, Fv/Fm, is the preferred metric for quantifying the loss of photosystem II (PSII) function in photosynthetic algal symbionts (Symbiodiniaceae) of reef-building corals exposed to heat-stress, particularly at the early stages of coral bleaching. Loss of PSII function can be quantified as the temperature at which a holobiont loses 50% of maximum photochemical efficiency (50% effective dose, or ED50) when exposed to a range of experimental temperatures. Here, we demonstrate that dose-response curves can be substantially more informative about a coral’s stress response by including ED5 (5% effective dose), ED95 (95% effective dose), and Decline Width (ED95–ED5) values in summary statistics. These parameters are commonly used in plant ecophysiology and can be extracted from fitted Fv/Fm temperature response curves. This suite of metrics provides a broader understanding of the loss of PSII function in acute thermal stress experiments in corals and could enhance comparability among coral and plant studies