Ten individual colonies of each phenotype per species were sampled on September 1, 2022. Four fragments were collected from each individual colony (i.e., genetic clones) by hand using bone cutters, totalling 160 fragments. Following collection, corals were transported to the Hawaiʻi Institute of Marine Biology (HIMB) and placed in outdoor, flow-through seawater tanks under ambient temperatures (mean ± SD; 28.2 ± 0.1°C, n=2 tanks) until experimentation. Coral thermal tolerance experiments were initiated 72 hours after collection. The experimental heat stress assay followed the standardized temperature profile used to measure heat tolerance in corals (e.g., MMM, MMM+3°C, MMM+6°C, and MMM+9°C) (Voolstra, et al., 2020). The experiment began on September 4 2022 at 13:00 with a 3-hour ramp to respective treatment temperatures (27.5°C, 30.5°C, 33.5°C, 36.5°C), a 3-hour hold, and a 1-hour ramp down to MMM temperature (27.5°C). A fragment from each coral colony was suspended using fishing line and randomly placed into each treatment, so that all genotypes across species were present in each treatment. Temperatures were controlled using a custom computer controlled system (Raspberry Pi). Temperatures were constantly monitored and manipulated by responding to probe measurements in real time, and recorded using cross-calibrated temperature loggers (accuracy: ± 0.47°C at 25°C; resolution: ± 0.10°C at 25°C HOBO UA-001-64, Onset Computer Corporation). Experiments were performed outdoors under natural photosynthetically active radiation (PAR), which ranged between 515–580 µmol m-2 sec-1 at midday (~12:00; Licor cosine sensor). At the end of the ramp and 1 h after sunset (~19:30), corals were assessed for dark-adapted photochemical yield (Fv/Fm) using a Diving-PAM (Walz GmbH) 5-mm diameter fiber-optic probe at a standardized distance (5 mm) above the coral tissue after F0 stabilized. Three random spots (2–3 cm apart across the front and back of the nubbin) were measured on each fragment to obtain average measures of Fv/Fm. All readings with F0 values that were less than 110 were removed to avoid any false detections (Marzonie et al., 2022). The following morning at 07:00 corals were photographed with a color standard (WDKK Waterproof Color Chart, DGK Color Tools) to assess coral color, a proxy for bleaching severity. Bleaching severity was determined visually (e.g., 0, 20, 40, 60, 80, 100% white) (Evensen, et al.., 2022) using the six gray standards as a reference (e.g., black= 0% bleached, white = 100% bleached) from two photographs (front and back of the fragment) to obtain an average color score (Brown et al., 2023 Fig. S4).