‘Pink paint’ by Cathy Cole.

Coralline algae ‘pink paint’ is the foundation of New Zealand’s rocky reef ecosystems, but it is immediately threatened by ocean acidification. An unsung hero, it’s rough surface nurtures life from microscopic plankton to our great kelp forests. Data from the Munida Transect, offshore Otago, are printed here in acrylic and watercolour showing rising carbon dioxide (top) and falling pH (bottom) in the surface waters from season to season over the past two decades and more. An empty ocean looms, open to invasive species to take over.