Early victims of ocean acidification could go extinct this century

Increasing ocean acidification could lead to the extinction of an entire class of marine organisms by 2100 say a team of scientists from the Australian Institute of Marine Science (AIMS).

"Forams – or foraminifera – are much like an amoeba with a shell," explains Dr Sven Uthicke, lead author of the study which was published last week in the prestigious scientific journal Scientific Reports, an online journal of Nature. "As CO₂ levels increase, our oceans will become more acidic, making it more difficult for these small marine creatures to form the shells they need to survive.

"These simple organisms are vulnerable to increasing ocean acidification as they lack the complexity and energy reserves of other skeleton-based marine creatures, like corals and sea urchins.

"We conducted a study in Papua New Guinea, where subsurface volcanic activity has caused naturally-occurring CO₂ to continuously bubble up from the seabed. These "CO₂ seeps" have created localised changes to seawater acidity similar to those expected throughout the world's oceans by the end of this century if CO₂ emissions continue unabated.

"These seeps provide important clues to what the marine world might look like in the future," he says.

"Our analysis of samples collected more than half a kilometre from these seeps revealed healthy and diverse communities of forams, similar to those you would find on the Great Barrier Reef. However, the samples we took closer to the seeps, where CO₂ concentrations were higher, showed a very different picture.

"In the high CO₂ conditions closer to the seeps, the water was more acidic, and disturbingly the number and diversity of forams was significant lower. We also observed intermediate effects of acidification on forams such as corroded or ‘pitted' shells.

"Of most concern, not one single species of foram was found in samples drawn from locations where conditions had already reached acidification levels predicted for our oceans by 2100 in all but the most optimistic emissions scenario."

The results echo mass extinctions of marine organisms that occurred millions of years ago, when the Earth experienced significant increases in CO₂, temperature or both. Although some forams were able to survive during these past events, the current rate of CO₂ increase is much faster than anything seen before.

"In previous studies at these seeps we looked at the response of other organisms, such as corals – we found similar if less dramatic results – many coral species were unable to grow in these increasingly acidic conditions," says Dr Katharina Fabricius, a co-author of the present study.

"In the grand scheme of things, the small and simple nature of forams might make them seem fairly unimportant compared to say, corals.

"However, foram shells account for up to 40% of the composition of some cays and sandy sea beds of coral reefs – and these habitats are home to a significant number of coral reef species such as seabirds and turtles.

"Of course the long-term implications of any disappearance of forams from the reef are not certain and will require further investigation, but these findings do add to concerns regarding the health resilience of coral reefs if ocean acidification progresses as predicted under current CO₂ emission scenarios.

The paper "High risk of extinction of benthic foraminifera in this century due to ocean acidification" by S. Uthicke, P. Momigliano and K. E. Fabricius appears in the Nature Publishing journal Scientific Reports. (http://www.nature.com/srep/2013/130503/srep01769/full/srep01769.html).

More Information:

Dr Sven Uthicke, Senior Research Scientist, AIMS, office: (07) 4753 4483 or mobile: 0447825604,

email: s.uthicke@aims.gov.au

AIMS media contact: Steve Clarke, office: (07) 4753 4264 or mobile: 0419 668 497

email: s.clarke@aims.gov.au