To rule out the possibility that the observed shift in host:symbiont signal ratio is largely influenced by the increase of host-derived signal, we first analyzed the expression of pa-GFP in treated corals at 5 days (Fig. S5) and saw that even though the expression of pa-GFP differs between PC and NPC corals (it decreases in NPC corals but remains stable in PC corals), it does not change between ven- and ven+ treatment in PC or NPC corals. The expression of pa-GFP cannot thus explain the differences between signal ratio shift in ven+ PC and ven- PC corals.