A contribution to the special feature 'Ocean acidification'. Ocean acidification poses a range of threats to marine invertebrates; however, the emerging and likely widespread effects of rising carbon dioxide (CO 2 ) levels on marine invertebrate behaviour are still little understood. Here, we show that ocean acidification alters and impairs key ecological behaviours of the predatory cone snail Conus marmoreus. Projected nearfuture seawater CO 2 levels (975 matm) increased activity in this coral reef molluscivore more than threefold (from less than 4 to more than 12 mm min 21 ) and decreased the time spent buried to less than one-third when compared with the present-day control conditions (390 matm). Despite increasing activity, elevated CO 2 reduced predation rate during predatorprey interactions with control-treated humpbacked conch, Gibberulus gibberulus gibbosus; 60% of control predators successfully captured and consumed their prey, compared with only 10% of elevated CO 2 predators. The alteration of key ecological behaviours of predatory invertebrates by near-future ocean acidification could have potentially far-reaching implications for predator -prey interactions and trophic dynamics in marine ecosystems. Combined evidence that the behaviours of both species in this predator -prey relationship are altered by elevated CO 2 suggests food web interactions and ecosystem structure will become increasingly difficult to predict as ocean acidification advances over coming decades.

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