Naturally acidified reefs Papua New Guinea

In Papua New Guinea, subterranean volcanic carbon dioxide seeps up through the ocean floor, causing localized ocean acidification-like conditions. Reef communities around these CO2 vents are different and habitat structures are less prolific. We wanted to find out why.


Deployment of BARS

We glued domino-sized pieces of coral skeleton to plastic bases to mimic natural reef frameworks. We deployed these along the natural acidification gradient and waited to see how they would change in two years. The images to the left show the experimental rocks with invertebrates and coral growing on top of them.

Looking inside coral skeletons with Micro CT

We used high-resolution microCT to visualize how the blocks have changed inside and out. This machine creates 3D x-ray images at resolutions up to 7 microns, less than a 20th of the diameter of a human hair. This video shows one of these scans. The new calcium carbonate "accreted" to the coral skeletons by crustose coralline algae is green andholes created by worms dissolving away the coral rock are in red. The balance of these two opposing processes (accretion and erosion) are responsible for the permanence of these skeletons, and the persistence of coral reef habitat.



These graphs show erosion (macroboring by worms) on the left and accretion (new calcified material) on the right. Red and blue represent data from two CO2 seep sites in Papua New Guinea. You can see how macroboring increases in more acidic (lower pH conditions) and how accretion decreases due to acidification at one site. We can expect similar changes on reefs worldwide due to global ocean acidification. When erosion becomes greater than accretion, reefs dissolve away, turning to rubble and sand versus healthy high-biodiversity ecosystems.