Coral reef organisms that help build homes for thousands of other species face extinction by 2100, thanks to increased CO2 levels and ocean acidification.

Researchers from the Australian Institute of Marine Science have discovered that ocean acidification around naturally occurring CO2 seeps in Papua New Guinea offer a glimpse of a future high-CO2 world and its impact on coral reef ecosystems, including the possible complete loss of creatures called Foraminifera, or forams.

“We found no Foraminifera species at all where acidification had reached the predicted level of our oceans in 2100, in all but the most optimistic emissions scenarios,” says Sven Uthicke, a senior research scientist.

Forams are amoeba-like organisms covered in shells. These shells make up to 40 per cent of some cays or sandy sea beds of coral reefs—the home to many coral reef species.

The team discovered that foram communities close to the high-CO2 seeps had lower species diversity and were less abundant than those 500 metres away. It also found that foram shells were corroded or ‘pitted’ by the acidic environment.

“Forams are particularly vulnerable to ocean acidification as they lack the complexity and energy reserves of other marine creatures with carbonate skeletons, such as corals and sea urchins.”

But the corals also showed the effects of increasing acidity, with branching and leaf-like corals being replaced by simpler, boulder-like species close to the seeps.

“The decline of the structurally complex corals means the reefs will be much simpler and there will be less habitat for the hundreds of thousands of species we associate with today’s coral reefs,” says study leader Katharina Fabricius.

Photo: Bubbles of CO2 rise from a natural seep in PNG.

Credit: K.Fabricius © AIMS

Australian Institute of Marine Science, Steve Clarke, Tel: +61 7 4753 4264, media@aims.gov.au, www.aims.gov.au/co2_seeps