To determine if the shift in red to green signal ratio is caused by an increased level of pa-GFP in coral tissue as a response to heat stress, we analyzed pa-GFP expression via qPCR in PC and NPC corals during heat stress (Fig. S1). pa-GFP is downregulated during the first three days of acute heat stress in both PC and NPC corals, so the bleaching rate is unlikely to be connected to the increased signal derived from host tissues.