It has long been a widely held belief that zooxanthellate need an adaptation period of weeks when exposed to increases/decreases in light intensity. I've got data from experiments done just before I left Hawaii that showed zooxanthellate chlorophyll content can ramp up or down in short time (one day) when light intensity shifts. The coral was tentatively identified as Porites lobata. The experiment's intent was to examine the effect of iron addition and the possibility of reduced chances of bleaching. As happens, unexpected results were observed. The question is if the same happens in other coral genera.