Animals died in 'toxic soup' during Earth's worst mass extinction: A warning for today

In freshwater lakes, toxic microbial blooms are becoming more common. Credit: Christian Fischer/Wikimedia Commons
The end-Permian mass extermination event, which occurred approximately 252 million years ago, was caused by massive volcanic emissions of greenhouse gasses, major temperature rises, and almost all species loss in the oceans.

It seems that rivers and lakes are no longer safe havens. Recent research by an international team of scientists, including Professor Tracy Frank, Head of the Department of Geosciences, and Professor Chris Fielding, both recently arrived at UConn has revealed a new cause of extreme warming-related extinction: toxic microbial blossoms.

As a waste product from their photosynthesis, microscopic algaes and cyanobacteria are essential for a healthy ecosystem. When their numbers are out of control, the microbes can deplete oxygen and release toxic substances into the water. The researchers examined the chemical, fossil and sediment records of rocks close to Sydney, Australia. They discovered that there had been several spikes in bloom events shortly after the eruptions of the end Permian mass extermination. After the "detritivores", or bottom-feeding animals, were gone, there was no way for microbes to be controlled. For millions of years, the freshwater systems became awash with bacteria and algae, stalling the recovery of animals.

Frank and Fielding are sediment researchers. Frank explains that their contribution to the research, which took place while they were both at the University of NebraskaLincoln was in extracting information about the environment and toxic soup from layers of sediment.

Frank states, "We are trying understand the conditions these plants lived in, for example were they river deposits or lake deposits." The geochemistry can provide details about the water's salinity and temperature.

Three main ingredients of the toxic soup include accelerated greenhouse gas emission, high temperatures and abundant nutrients. The first two were caused by volcanic eruptions, and the third was caused by sudden deforestation. The soils left behind by the trees were carried into rivers and lakes. This provided all the nutrients the microbes needed. The fossil records of various warming-related mass extinctions were very similar when the team compared them. This suggests that deadly microbial outbreaks are repeat offenders in freshwater extinctions caused by extreme warming.

Humans today have been following this recipe. Freshwater microbial blooms are on the rise. This demonstrates how important geosciences are in understanding past events in ways that provide context for understanding current climate changes.

Frank states that toxic algae blooms are increasing in lakes and shallow marine environments. This is due to changes in plant communities and temperature, which in turn leads to increased nutrient inputs to freshwater environments. There are many parallels between today and yesterday. Although volcanism was an important source of CO2 in the past, we know that it was comparable to today's CO2 increases due to anthropogenic causes.

"We can see how climate has changed over time, the extremes, how fast it can change and what its causes are. This gives us a good background for understanding today's climate.

The Intergovernmental Panel on Climate Change's (IPCC) report for this year states that humans have an "unambiguous" influence on climate change, creating conditions that encourage the growth of warmth-loving microbes. This has resulted in a sharp rise in toxic blooms, mainly due to an increase of nutrients from water polluting, mostly from agriculture, and deforestation. The result: massive fish deaths, severe health effects for humans and animals, and a cost that is estimated at billions of dollars annually.

Fielding says, "The end-Permian can be a great place to find parallels with what's going on now."

"The other parallel is that the Permian temperature increase coincided with huge increases in forest fires. Fire was one of the main factors that decimated entire ecosystems, as we can see right now in California. It is difficult to predict the long-term effects of such events as they become more common.

These are obvious signs of an imbalanced ecosystem. The present study shows that bloom events can have a long-lasting impact on the ecosystem. We have the ability to prevent toxic blooms, and avoid mass extinctions like the species that experienced them in the past.

"The frightening thing is that we have become accustomed to thinking in terms timescales of many years, sometimes even tens of thousands of years if we get really wild. It took four million years for the end-Permian mass extermination event to be recovered. Fielding says that is quite alarming.

Learn more Mass extinction is likely to be caused by volcanic CO2 venting

Further information: Chris Mays and colleagues, Lethal microbes delayed freshwater ecosystem recovery after the end-Permian extinct, Nature Communications (2021). Information from Nature Communications Chris Mays and colleagues, Lethal microbes delayed freshwater ecosystem recovery after the end-Permian extinct, (2021). DOI: 10.1038/s41467-021-25711-3