What oceans surround Western Australia

Marine heat wavesForest fires in the ocean

In February 2011, the water temperatures rose off Western Australia, up to 30 degrees Celsius. Over hundreds of kilometers, kelp forests and seagrass meadows disappeared within a few weeks, coral reefs bleached out, marine animals died: the event went down in scientific literature as the "Ningaloo Niño" and was an ecological catastrophe. Daniel Smale of the Marine Biological Association in Plymouth then decided to investigate the phenomenon of "sea heat waves":

"Among other things, we wanted to investigate the question of whether these heat waves in the oceans have become more frequent and intense as a result of climate change. And our analyzes show that the number of days with significantly higher sea temperatures has increased by 54 percent worldwide over the past few decades."

Heat waves also occur in the polar ocean

Sea heat waves, which also occur naturally, are increasing significantly in number and intensity due to climate change. A number of factors play a role in their formation: the shifting of warm currents, for example, the heating of the sea surface by hot air, winds, climatic phenomena such as El Niño. No sea is safe from them:

"We have experienced this several times in the last few winters in the Arctic, for example, when the water temperatures were three, four, five degrees too high for the time of year."

Fatal domino effect

To assess the impact on ecosystems, the team analyzed 116 research papers on eight well-studied ocean heat waves - including the record-breaking "Ningaloo Niño" from 2011. According to this, such events are, so to speak, the marine equivalent of devastating forest fires:

"When large kelp forests or seagrass meadows die, it can trigger a domino effect: important habitats disappear with them and biodiversity decreases. Our analyzes also show that regions in the western Atlantic or the eastern Pacific are particularly sensitive to heat waves. One reason for this is that there Many species live that are already reaching their limits: They can barely cope with the increased temperatures caused by climate change. If a sea heat wave warms the water quickly, it is likely that they will die. "

The consequences remain noticeable for a long time

Since the heat waves cause the water temperatures to rise over a large area, even fish often cannot escape to cooler zones. Daniel Smale warns: Humans have already exposed the oceans to many threats: litter, acidification, over-fertilization.

"But to me as a marine ecologist, it looks like climate change, and especially these marine heat waves, will rapidly transform coastal ecosystems and biodiversity. Climate change is likely to exacerbate these sea heat waves, making them the greatest threat to the oceans."

In Western Australia, the aftermath of the 2011 heat wave can still be felt: even though the reefs have recovered, the kelp forests have not grown back.