A new report warns that the health of the world's oceans is deteriorating even faster than had previously been thought.
The International Programme on the State of the Ocean says oceans being heated by climate change are also being turned slowly less alkaline by absorbing CO2.
They are also suffering from overfishing, pollution and dead zones formed by fertiliser run-off.
The international report warns that conditions are ripe for the sort of mass extinction event that has afflicted the oceans in the past.
Report co-ordinator Professor Alex Rogers from Oxford University, says ocean acidification is causing effects that no-one anticipated, such as fish becoming unable to properly detect their surroundings.