Thermal fluctuations and extreme events threaten marine ecosystems

A study by the University of Pisa, in collaboration with the Sant'Anna School of Advanced Studies, and published in Nature Communications reveals how ongoing climate change will affect the ability of marine microorganism communities to cope with future extreme events.
The Calafuria cliffs in the province of Livorno were the natural laboratory at the center of a study by the University of Pisa and the Sant'Anna School of Advanced Studies to understand how climate change is altering the stability of coastal microbial communities. The research, published in the journal Nature Communications, analyzed how the biofilm - a thin living film formed by microalgae and bacteria that covers the reefs and is fundamental for the life of the reefs - reacts to variations in air temperature.

The researchers conducted a field experiment exposing the biofilm to two different thermal regimes: constant heating and one characterized by strong oscillations, which simulates the unpredictable conditions destined to become increasingly common in the near future due to climate change. The results showed that a constant heating regime favors the presence of species with similar functions, able to “take turns” in case of difficulty. This mechanism allows the biofilm to better resist future extreme events. On the contrary, strong temperature fluctuations reduce diversity by favoring fast-growing species, capable of recovering quickly after a thermal shock, but functionally more vulnerable in the long term.

“Climate change does not only manifest itself through an average increase in temperatures, but also through an increase in thermal variability, that is, unpredictable oscillations between peaks of heat and less warm periods,” says Luca Rindi of the University of Pisa, first author of the study. ”In a world that is becoming increasingly warm and unstable, marine microorganisms could, on the one hand, react more quickly to shocks, but on the other hand become more vulnerable in the face of extreme events repeated over time. In view of the challenges that the climate holds for us, the study opens a window on the future, helping us to understand how this important element of the coastal ecosystem will react to future climate changes.”

The experiment was conducted along the coast of Calafuria, near Livorno, an area characterized by rocky sandstone platforms exposed to the air at low tide, an ideal environment for studying marine biofilm in natural conditions. To simulate the increase in temperature, the researchers used special metal chambers heated with small stoves, monitoring the variations in heat with electronic sensors. To evaluate the biofilm's response, they used an infrared camera capable of detecting the amount of chlorophyll. Finally, thanks to the collaboration with the Institute of Plant Sciences of the Sant'Anna School of Advanced Studies in Pisa, the DNA of the microorganisms was analyzed with advanced sequencing techniques, similar to those used to study the human genome, to understand what functions the different species perform and how their genetic heritage makes them more or less suited to respond to extreme events.

“The success of this collaboration demonstrates once again the value of the Pisan university system”, says Matteo Dell'Acqua, Director of the Institute of Plant Sciences at the Sant'Anna School and co-author of the study. He continues: ‘the union of the unique skills present in our territory allows us to explore the frontier of research on the effects of climate change’.

The University of Pisa played a central role in the study, in particular through the Department of Biology, where some of the study's main authors, such as Luca Rindi and Lisandro Benedetti-Cecchi, worked. The university also provided scientific and logistical support for the design and implementation of the field experiments, as well as contributing to the analysis of ecological and microbiological data thanks to the support provided by the Green Data Center.
 

The project was partly funded by the European ACTNOW program (Advancing understanding of Cumulative Impacts on European marine biodiversity, ecosystem functions and services for human wellbeing), which studies the cumulative impacts of climate change on marine ecosystems.