Increasing acidity

Ocean acidification is the highest ranked threat to marine habitats. Carbon dioxide is absorbed from the atmosphere. Once in water, it is converted to carbonic acid, raising the acidity of the ocean. Naturally, the ocean is neutral or slightly basic, and the organisms within it are suited to these conditions. Scientists think that the ocean acidity has increased by about 30% in the last 100 years. In Otago, a 7.1% increase in ocean acidity has been observed since the turn of the century.

Shell-forming organisms such as shellfish, corals and some types of plankton are highly affected by the acidification. The carbonate that many organisms use to build their shells becomes less available as acidity increases, so many animals will struggle to grow their protective shells. Larvae may be deformed and unable to swim as they should, meaning that they will be unable to survive or settle in the appropriate habitat, thus decreasing the overall recruitment success of this species.

Download the Department of Conservation infographic as a PDF.