Abstract Summary
The ability to predict metabolic deficits in coral holobiont metabolism is becoming increasingly important as water temperatures continue to rise. Physiological sensitivities to acute and cumulative thermal stress were compared in Acropora cervicornis from Broward County, Florida. Dark-adapted chlorophyll fluorescence and rates of respiration and photosynthesis were measured in acute and cumulative exposures at five temperatures spanning 25-36˚C. Each exposure revealed differences in metabolic sensitivity, determined by Q10 and critical thermal maximum (CTmax). CTmax was lower with cumulative stress exposure than acute stress. Acutely stressed corals had a drastic metabolic response to thermal stress when exposed to temperatures that exceeded present day naturally-occurring maxima and were nearly two times more sensitive than corals that experienced a more gradual exposure. In contrast, when heated gradually, metabolic rates appeared to be less sensitive to temperature until CTmax was reached. A temperature-based model of the ratio of daily gross photosynthesis to respiration (Pg:R) was derived from these measurements to provide real time metabolism with in situ temperature data. Remarkably, Pg:R model predictions agree with the thermal bleaching threshold for this species. Pg:R models from both exposures suggest acclimation potential in this population may be metabolically limited. Temperature-based metabolic models may be a useful tool to identify other at-risk species, prioritize restoration target regions, and predict the timing of greatest vulnerability to focus restoration efforts.
