While ocean acidification is predicted to threaten marine biodiversity, the processes that directly impact species persistence are not well understood. For marine species, early life history stages are inherently vulnerable to predators; hence the ability to detect predators can be critical for survival. Whether or not acidification inhibits predator detection is unknown.

Results/Conclusions
We showed that newly hatched fish larvae detect predators using olfactory cues and this ability is retained through to settlement. Aquarium-reared larvae, not previously exposed to predators, were able to distinguish between the olfactory cues of predatory and non-predatory species. However, exposure to seawater simulating near-future levels of ocean acidification, caused settlement-stage larvae to become strongly attracted to the smell of predators and the ability to discriminate between predators and non-predators was lost. In the field, CO₂ treated larvae exhibited bolder behavior compared to the current day control larvae, which translated to increased mortality.  An increase in CO₂ concentrations in the ocean could have serious consequences for the replenishment and the sustainability of marine populations.