Heat-stressed PC and NPC corals showed a very mild increase in caspase-3 activity (< 2-fold) suggesting that some coral cells might undergo apoptosis but at a significantly lower rate than in the case of colchicine-induced coral bleaching (Figure 5A). Inversely, we observed a clear positive trend in APs activity over time in all heat-stressed corals, but significantly higher in NPC corals when compared to PC corals (ANOVA, activity ~ conditioning + time + (1|Coral), p(time) <0.001, p(conditioning) = 0.0023). The APs activity in heat-stressed NPC corals at 72h was similar to the APs activity in rapamycin-treated corals, suggesting autophagy is the prevalent programmed cell death in thermally bleaching P. acuta in Kāneʻohe Bay, Hawai‘i.