Figure 1. Setup for measuring extracellular superoxide production (A) and superoxide detoxification activity (B).

(A). Coral O₂ ⁻ production was measured using a temperature controlled stirred flow-through chamber and algal O₂ ⁻ production was measured using an online syringe filter. Filtered seawater (FSW) was pumped through the chamber or the syringe filter and the O₂ ⁻ signal was recorded downstream. (B). Coral O₂ ⁻ detoxification activity was measured by adding O₂ ⁻ spikes to seawater previously incubated with corals. Calibrations and controls were done in a similar manner with FSW. Both sample and reagent were drawn into a spiral flow cell at a rate of 5 mL min⁻¹ and the emitted light was collected by a PMT and reported to a personal computer. To shorten the time O₂ ⁻ spent in the line the sample was drawn directly into the flow cell while the reagent and waste lines were drawn with a peristaltic pump. To eliminate contamination by trace metals and prolong O₂ ⁻ half life, the filtered seawater used for the measurements were amended (and pre-equilibrated) with 150 µM DTPA.