Papua New Guinea's volcanic bubbles a glimpse at future of coral

By the end of this century, coral reefs in Australia and around the world could be slower to recover, structurally simpler, and increasingly dominated by fleshy algae as rising carbon dioxide reshapes ocean chemistry.

These are the predictions that new international research – published this week in Communications Biology – is warning against, as scientists present a volley of stark new findings about the current and long-term impact of a process known as ocean acidification.

As the oceans absorb more carbon dioxide from the atmosphere, they are becoming increasingly acidic – eroding the very calcium carbonate skeletons that build coral reefs. Yet despite decades of laboratory studies and ecosystem models, scientists have lacked real-world systems that reflect how entire reef communities respond to these long-term chemical shifts.

Researchers from the Australian Institute of Marine Science (AIMS) have now filled that gap by studying shallow-water reefs naturally bathed in volcanic CO₂. These reefs, located near remote submarine vents in Papua New Guinea’s Milne Bay Province, experience chronic exposure to elevated carbon dioxide, offering scientists a rare preview of the seascapes expected under future emissions scenarios.

“These unique natural laboratories are like a time machine,” said Dr. Katharina Fabricius, senior author of the study and a coral ecologist at the Australian Institute for Marine Science (AIMS). “The CO₂ seeps have allowed us to study the reefs’ tolerance limits and make predictions. How will coral reefs cope if emissions align with Paris Agreement targets? And what happens if they don’t?”

Fabricius first encountered the phenomenon in 2000 when she noticed streams of bubbles rising through coral gardens while surveying species diversity. Nearly a decade later – and spurred by growing concern over ocean acidification – she returned to analyse the gas and found it was almost pure CO₂.

It’s this discovery that launched a decade-long research initiative investigating how tropical marine ecosystems adjust, adapt, or falter after generations of exposure to acidified conditions.