Thermal extremes likely trigger metabolic imbalance in coral holobionts

Coral reefs are facing increasingly frequent and intense periods of
anomalously high temperatures in the Anthropocene. Metabolism scales
directly with temperature and we hypothesized that at peak temperatures
oxygen consumption may outpace photosynthetic oxygen production in coral
holobionts, leading to metabolic challenges, particularly at night when
photosynthesis is not occurring. To investigate this we compiled a dataset
of metabolic rates extracted from the published literature of respiration
and photosynthetic rates of corals and then modelled these rates using a
thermal performance curve approach. From this we could estimate the
thermal optima (Topt), activation energy (E) and deactivation energy (ED)
of each metabolic rate. We found a largely consistent trend across
latitudinal regions and taxa that net photosynthesis peaks at temperatures
lower than respiration, and begins to decline while respiration is still
increasing impacting the oxygen budget of the holobiont. This dataset
includes the rates per temperature that were extracted for each published
article for respiration, net photosynthesis and gross photosynthesis. P:R
ratio was calculated from these values, as well as gross or net
photosynthesis in the case where one of these rates was missing. The full
methods is available in the associated manuscript on how studies were
selected. All rates are expressed as μmol O2 cm-2 h-1 except in the case
of P:R ratio, which is unitless. We also included pertinent information
from each study such as the coral species, location the corals were
collected from, the temperature, light conditions, number of replicates,
experimental duration where applicable as well as the ramping rate and
references.