A future look: how corals will cope under combined pressures

A new study has shown climate change will have serious consequences for the ability of baby corals to cope with elevated sediments occurring inshore in the Great Barrier Reef.

The study, held in the Australian Institute of Marine Science’s (AIMS) National Sea Simulator, is the first of its kind to look at the combined impacts of sedimentation and climate change on the early life of corals.

The study revealed the young corals raised under warmer, more acidic ocean conditions predicted for the end of the century were more likely to perish than young corals under current conditions, when exposed to present day sediment levels.

AIMS lead researcher and James Cook University (JCU) PhD candidate Christopher Brunner said the study was important in understanding how these pressures interact.   

 “What is different about this study is that we are not only looking at the impacts of climate change on young coral – we are looking at this impact combined with poor water quality, namely increased sedimentation,” he said.

 “We found older and larger corals were more resistant to sediments. We also discovered coral recruits grown in current climate conditions were more likely to survive the highest tested sediment concentrations.”

 “When we raised the temperature and acidity of the water to simulate the future climate, the corals' ability to cope with increased sediment levels diminished.” 

“This suggests that these millimetre sized corals will become more sensitive to sediment stress as the climate changes.” 

The study used the National Sea Simulator’s sophisticated control systems to grow the baby Acropora millepora corals for 14 weeks while simulating future climate conditions.

The team simultaneously exposed the corals multiple times to various sediment concentrations that may occur in calm inshore reefs, near river runoff and dredging operations.

 AIMS’ Principal Research Scientist Dr Andrew Negri said the survival of young corals is critical for the maintenance of coral populations, and for the recovery of coral reefs in the face of other impacts related to climate change.

 “The Reef is under a number of different pressures, and none of these occur in isolation,” Dr Negri said. 

 “It's important we understand how other pressures impact reefs and their ability to recover – not only now but also in the decades to come.” 

 “Climate change is the biggest threat to coral reefs – and this research informs future water-quality guidelines on the Great Barrier Reef that will need to be climate-adjusted.”

The research was supported by AIMS@JCU and the Australian Government’s National Environmental Science Program (NESP) Tropical Water Quality Hub.

The research paper ‘Climate change doubles sedimentation-induced coral recruit mortality’ was published in the Science of the Total Environment journal.

Feature image: PhD student Christopher Brunner conducting experiment at AIMS' National Sea Simulator / Credit: Christopher Brunner