Dataset: Physiology measurements on collected coral pairs from Kaneohe Bay, Oahu, HI between July and December 2019

At the peak of a marine heatwave in 2015, 10 pairs of visually bleached and non-bleached colonies of Montipora capitata and Porites compressa adjacent to each other on the reef were identified, gps-marked and tagged with cattle tags. Before, during, and after the 2019 marine heatwave, these pairs were photographed with size and color standards. At each time point, 1 fragment (~4 centimeters) and 1 biopsy (~2 centimeters) were collected from each colony. The fragments were then transferred in ambient seawater to an outdoor flow-through seawater table for physiological measurements and the biopsies were snap-frozen in liquid nitrogen for future molecular assays

The volume of each coral fragment was measured via the water displacement method.

Photochemical efficiency was measured on each coral fragment approximately 1 hour after sunset on the same day of collection. Measurements were made using the Diving-PAM 5-millimeter diameter fiber-optic probe at a standardized 5 millimeters above the coral tissue after F0 stabilized. The Diving-PAM settings were set to a measuring light intensity of 5, gain of 2, and saturation pulse intensity of 5.

Within 3 days of collection, rates of photosynthesis and respiration were measured on each coral fragment by quantifying oxygen evolution and consumption. Each coral fragment was placed in a 250 milliliter (mL) sealed chamber filled with ambient seawater surrounded by a temperature-controlled water jacket to maintain a constant temperature (ambient: 25-27°C). Seawater in the chambers was constantly mixed using a magnetic stir bar. Temperature and dissolved oxygen concentrations were measured using a Pt100 temperature probe and PSt7 oxygen optode (PreSens), respectively, inserted through a port in the lid of each chamber. Oxygen optodes were calibrated on each measurement day with a 0% oxygen solution (0.01 gram per milliliter (g mL-1) NaSO3) and 100% air saturated seawater. Oxygen evolution rates were measured at steady increments of light (112–726 micromole: per second and square meter; µmol m-2 s-1), increasing light intensity only after a steady slope was achieved for all fragments for at least 10 minutes. After the maximum light level, the lights were turned off and oxygen consumption rates were measured until a steady slope was achieved for at least 10 minutes. Temperature and oxygen data were recorded every 3 seconds. Corals were then snap frozen and stored at -80°C until further processing.

Tissue was removed from each fragment using an airbrush containing phosphate-buffered saline solution. The resulting tissue slurry was homogenized at 25,000 rpm for 10 seconds using tissue and aliquoted for subsequent assays.

For symbiont cell counts, tissue homogenate was homogenized at 25,000 rpm for 10 seconds followed by needle shearing with a 22-gauge needle. Algal cells were then pelleted by centrifugation at 7,000 g for 5 minutes and resuspended in 0.1% sodium dodecyl sulfate (SDS) in 0.22 micrometer filtered seawater. Symbiont concentrations were determined by flow cytometry. Symbiont cells were excited with a blue laser (488 nanometers) and identified by analyzing forward scatter and red autofluorescence in GuavaSoft 3.4 with the same gating for all samples.

Chlorophyll was extracted in 100% acetone. Tissue homogenate was centrifuged at 14,000 rpm for 3 minutes at 4°C and the supernatant was removed. The remaining pellet was incubated in 100% acetone for 32-48 hours in the dark at -20°C. The samples were then centrifuged at 14,000 rpm for 3 minutes at 4°C. The supernatant was transferred to a 96-well flat bottom glass plate and absorbance was quantified by measuring absorbance at 630 nanometers, 663 nanometers and 750 nanometers on a plate reader.

Soluble protein content was analyzed via the Bradford method using Coomassie Plus Bradford assay reagent. The crude tissue homogenate was analyzed to obtain a measure of holobiont protein. For the host fraction, symbionts were removed from the crude homogenate by centrifugation at 10,000 g for 10 minutes at 4°C, and the resulting supernatant was analyzed. The samples were mixed with the reagent on a plate shaker for 30 seconds, incubated for 10 minutes at room temperature and again mixed on a plate shaker for 30 seconds. The sample absorbance was then measured at 595 nanometers on a plate reader.

Ash-free dry weight was measured from a known volume of each homogenate dried at 60°C for 24 hours until a constant weight was achieved. After the dry weight was recorded, the homogenates were burned in a muffle furnace at 450°C for 6 hours. The samples were allowed to cool in the furnace before being weighed and the ash weight recorded.

Total antioxidant capacity was measured using the OxiSelect Total Antioxidant Capacity Assay Kit. The tissue homogenate was first centrifuged at 10,000 g for 10 minutes at 4°C prior to loading on the 96-well plate. Net maximum absorbance values were measured at 490 nanometers on a plate reader at the initial and final time points.

After tissue was removed, skeletons were soaked in 10% bleach for approximately 12 hours and then dried at 60°C for approximately 12 hours until a constant weight was reached. Surface area was determined by the single wax dipping method (Veal et al. 2010). Each skeleton fragment was pre-weighed before being dipped in paraffin wax, after which the final weight was recorded. The change in weight due to wax addition was compared against a standard curve of dipped wooden dowels of known surface area to calculate the skeletal surface area of each fragment.