Fragments of PC and NPC corals were live imaged with Zeiss LSM-710 confocal microscope at the beginning of the experiment and at days 3 and 5 of the heat stress to assess the rate of symbiont loss, or only at day 5 in the venetoclax experiment. EC Plan-Neofluar 2.5X/0.075 objective was used for the imaging resulting in total magnification of 25X. Images were acquired with Zen Imaging Software (Black edition) by Zeiss. Host cell fluorescence was excited with the 405nm laser and collected in emission range 454-621nm with master gain set at 650, digital gain 1.0, laser power 28%, and pinhole 35.5. Symbiodinium fluorescence was excited with the 405nm laser and collected in emission range 655-718nm with master gain set at 575, digital gain 1.0, laser power 28%, and pinhole 35.5. Fragments were kept in treatment temperature seawater (26°C and 32°C) during all microscopy. Three snap images of each fragment were taken using two fragments per treatment per colony, with a total of 6 colonies. Images were analyzed with ZEN Imaging Software. The ratio of green to red signal intensity (in fluorescence units) was analyzed in ten circular areas along the coral tissue (avoiding mouth and tentacles area) in each image. For a subset of images (2 colonies, all treatment/conditioning combinations), we also analyzed the intensity of individual signals (red, green) normalized to the circular area surface.