A baltic sea coastal environment

Stressed bacteria struggle to adapt to temperature changes

Research at a long-term heated bay near Oskarshamn provides a rare insight into how the Baltic Sea's coastal areas will be affected by climate change. Here, cooling water from the nearby nuclear power plant has raised the average temperature by on average five degrees Celsius for 50 years. New research shows that this prolonged warming stresses key bacteria and makes the ecosystem more vulnerable.

The combination of a warmer and more volatile climate expected in the Baltic Sea's coastal areas in the future spells trouble for the bacterial communities living in the seabed sediments, whose functions are crucial for maintaining stability in the ecosystem.

When the average temperature increases, the bacteria lose their ability to adapt to sudden temperature changes, such as heatwaves, according to a new experimental study published in the prestigious journal ISME Journal.

"These bacterial communities form the foundation of the ecosystem and regulate the flow of nutrients, energy, and greenhouse gases. If their species composition and function are disturbed, it has effects all the way up the food chain", says Anders Forsman, professor at the Department of Biology and Environmental Science and one of the co-authors of the study.

Simulating future weather phenomena

In the study, researchers examined how microorganisms living in the sediment of the long-term heated bay react to simulated heatwaves in a laboratory environment. For nine days, samples were exposed to temperatures between 6 and 35 degrees Celsius, while the activity in the bacterial communities was studied in detail. The patterns were compared with samples from a nearby unaffected bay that was also included in the experiment.

A realistic future scenario

The recently published results are part of Linnaeus University's extensive research in the long-term heated bay, supported by, among others, the Swedish Research Council and Formas.

"Much of the research on the effects of climate change in aquatic environments has been conducted in a laboratory environment with individual or a few species studied in detail. The long-term warming in this bay allows us to study an entire ecosystem in a realistic future scenario", says Mark Dopson.

The results show that the composition, species richness, and productivity of bacterial communities from the heated bay do not respond to temperature in the same way as in the adjacent bay, where the average temperature is more normal. One reason is that the bacteria are resource limited.

"Despite the fact that it has been 50 years since the temperature was raised in the bay, the bacterial communities we study have not fully adapted to the warmer climate. They are under constant stress, which makes them less good at handling sudden temperature differences", explains Anders Forsman.

Another discovery was that the bacteria from the long-term heated bay did not return and react normally when exposed to lower temperatures representing today's climate, indicating that they may have passed a 'tipping point' or threshold effect.

Difficult for life to adapt

The changed activity of the microorganisms in the bay demonstrates the challenge that rising average temperatures pose for life on Earth, the researchers believe.

"For the bacteria in the bay, a generation lasts only a few hours or days. Despite this, they have not managed to evolutionarily adapt to the warmer climate in 50 years. For many plants and animals, including us humans, it takes decades between each generation. This raises the question of whether the adaptations can keep pace with the ever-warmer world we are creating. We see this study as another reminder of the importance of taking strong measures to stop the warming", says professor Mark Dopson.

The results of the study have recently been presented to the United States Department of Energy.

More information:

Read the studies: Seidel, L., E. Broman, M. Ståhle, E. Nilsson, M. Ståhle, M. Ketzer, C. Perez Martinez, S. Turner, S. P. Hylander, J., A. Forsman, and M. Dopson. 2023. Climate change-related warming reduces thermal sensitivity and modifies metabolic activity of coastal benthic bacterial communities. ISME J 17:855-869.

Seidel L, M Ketzer, E Broman, S Shahabi-Ghahfarokhi, M Rahmati-Abkenar, S Turner, M Ståhle, K Bergström, L Manoharan, A Ali, A Forsman, S Hylander & M Dopson (2022) Weakened resilience of benthic microbial communities in the face of climate change. ISME Commun 2: 21.

The research project "Baltic Sea bays exposed to 50 years of warming can inform how biodiversity and ecosystem functioning respond to climate change"