Photosynthetic Irradiance Curves: Prior to experimental exposures, 10 coral fragments (5 per species) were used to generate a photosynthesis-irradiance curve to determine saturating irradiance for assessing rates of photosynthesis. Fragments were exposed to 10 light levels: 0, 15, 30, 60, 91, 136, 227, 416, 529, and 756 µmol m-2 s-1 generated by two LED lights (Aqua Illumination Hydra FiftyTwo) hung above the incubation chambers (described below). Rates of oxygen consumption or evolution were extracted using curve fitting of a non-linear least squares fit for a non-rectangular hyperbola (NLLS; Marshall & Biscoe 1980, Heberling 2013) was used to identify PI curve characteristics of each species. This model is as follows: = фPAR+√(φPPFD + Pmax)2-4ΘφPAR Pmax2Θ-Rd . Theta was set at 0.6 for M. capitata and 0.64 for P. acuta. Photosynthesis-irradiance curves were performed four times throughout the experiment on fragments of both species in the HTHC treatment to determine that there were no significant changes in Ik that occured during bleaching, and thus no need to change light settings used to measure respiration and photosynthetic rates.
Fragments were placed in individual respiration chambers (~610mL), with individual temperature (Pt1000 temperature sensor, PreSens) and fiber-optic oxygen probes (Oxygen Dipping Probes DP-PSt7, accuracy = ± 0.05% O2, PreSens) connected to a 10-channel oxygen meter (OXY-10 ST, accuracy = ± 1.0 °C, resolution = 0.1 °C, PreSens), to evaluate photosynthesis under saturating light conditions, as determined by PI curves described above, and light enhanced dark respiration (LEDR; Edmunds and Davies 1988). The respirometry setup consisted of 10 chambers with stirbars. Samples were measured in a series of runs that consisted of eight fragments (n=4 per species and n=2 blank chambers) per run, and exposed to PAR irradiance of 590 ± 7.16 µmol photons m-2 s-1 for 15 minutes to assess photosynthetic rates. Immediately afterwards, these fragments were exposed to dark conditions (0 µmol photons m-2 s-1) for 20 minutes to assess LEDR. Following respirometry, fragments were set back in their respective tanks.
