Figure 2: Diel variability in superoxide concentrations produced by Porites compressa.

To normalize coral-derived superoxide concentrations, superoxide levels in background seawater (SW) at 5–15 cm from the coral surface were subtracted. PAR values are indicated as grey circles. Periods of daylight (white) and darkness (black) are indicated in the horizontal scale at the top of the chart. Error bars indicate s.d. of the temporal signal collected at a rate of 0.5 points per second (n=21–124 points).