Against the backdrop of the United Nations COP26 Climate Conference in Glasgow next month, researchers from the University of East Anglia (UEA) and the Earlham Institute at Norwich Research Park have found that global warming is likely to cause abrupt changes to algae in our world’s oceans that could upset their eco-systems.

In a study conducted over more than 10 years and led by scientists from UEA, Earlham Institute, the US Department of Energy and the Joint Genome Institute in the US, climate change has been found to be the cause of the extension of the oceans’ warm hemispheres (the upper layer of the ocean above 15 degrees Celsius) towards both poles. It is likely to continue to do this for the next 100 years if action is not taken.

Instead of a gradual change in the oceans’ microbial diversity, the researchers suggest it will happen more abruptly at what they call ‘break points’ – whereby the upper ocean temperature averages around 15 degrees annually, causing a separation between cold and warm waters.

As the oceans warm, researchers predict that the ‘break point’ where cold, polar microalgal communities are replaced by warm, non-polar microalgal communities will move northwards through the seas around the British Isles.

This could result in major changes in the rest of the marine ecosystem and, because microalgae are key to the base of the food chain, there would be serious implications for fisheries, as well as marine conservation.

The ‘biological carbon pump’, whereby the ocean takes up carbon dioxide from the atmosphere, will change with this shift in microalgal communities – most likely becoming less effective – which could in turn amplify global warming.

The UK is one of the areas of the world most likely to be severely affected by this scenario and it could happen more suddenly than previously thought. However, the research team says that the changes can be prevented if we act swiftly to halt climate change now.

Prof Thomas Mock, from UEA’s School of Environmental Sciences, said: “Algae are essential in maintaining a healthy ecosystem to balance ocean life. By absorbing energy from sunlight, carbon dioxide and water, they produce organic compounds for marine life to live off.

“Algae and algal communities underpin some of the largest food webs on Earth. We wanted to better understand how the climate crisis is impacting algae worldwide – from the Arctic to the Antarctic. It appears that ocean temperature changes could have a significant impact upon the algae that our marine systems, fisheries and ocean biodiversity depend on.”

The study involved the first pole-to-pole analysis of how algae (Eukaryotic phytoplankton) and their expressed genes are geographically distributed in the oceans. The research team studied how their gene activity is changing due to environmental conditions in the upper ocean.

As the upper ocean is already experiencing significant warming due to rising CO2 levels, the researchers estimated how the distribution of these algal communities might change. They found that these global communities can be split into two main clusters: organisms that live in cold polar and warm non-polar waters.

Prof Mock explained: “Significant international efforts have provided some insights into what drives the diversity of these organisms and their biogeography in the world’s oceans.

“Our results provide new insights into how changing environmental conditions correlate with biodiversity changes that have been subject to large-scale environmental fluctuation and disturbances. This knowledge is essential for predicting the consequences of global warming and therefore may guide future environmental management.

“We can expect marine systems around the UK and other countries on the same latitude to be severely affected, and more suddenly than previously thought. The largest ecosystem change will occur when marine microalgal communities and their associated bacteria around the UK are replaced by their warm-water counterparts.

“This is expected to be caused by the pole-ward shifting ecosystem boundary or ‘biodiversity break point’ separating both communities. For this to take place, the annual average upper ocean temperature needs to become warmer than 15 degrees Celsius. It’s not irreversible though, if we can stop global warming now.”

Dr Richard Leggett at the Earlham Institute added: “This study also shows what an important role advances in DNA sequencing technologies have played in understanding ocean-based ecosystems. It has helped researchers shed more light on the biggest environmental challenges facing the planet enabling us to understand how we can put in place mitigating actions.”