Effects of ocean acidification on the potency of macroalgal allelopathy to a common coral.

Many coral reefs have phase shifted from coral to macroalgal dominance. Ocean acidification (OA) due to elevated CO is hypothesised to advantage macroalgae over corals, contributing to these shifts, but the mechanisms affecting coral-macroalgal interactions under OA are unknown. Here, we show that (i) three common macroalgae are more damaging to a common coral when they compete under CO concentrations predicted to occur in 2050 and 2100 than under present-day conditions, (ii) that two macroalgae damage corals via allelopathy, and (iii) that one macroalga is allelopathic under conditions of elevated CO, but not at ambient levels.