Climate affects microbial life around Antarctica

"Even at two locations that are only 400 kilometers apart on the peninsula (a very short distance on oceanographic scales), we found striking differences in the composition and relative abundances of microorganisms. These differences seem to be related to the differences in local climate", says NIOZ computational microbiologist Dr. Julia Engelmann. The results of this study by an international team of scientists led by NIOZ, are published in the journal Environmental Microbiome.

Coordinated measurements throughout one year

This study was a first, integrating data on bacteria and microbial eukaryotes (small organisms summarized as ‘microorganisms’, including phytoplankton). Samples were taken at two Antarctic research stations at the same time and along all seasons. In a concerted effort, researchers from NIOZ, collaborating universities in the US and the British Antarctic Survey, collected water samples from July 2013 to April 2014. This was done at the long term Ecological Monitoring site of the British Antarctic research station at Rothera, as well as close to the research station Palmer, located 400 kilometers to the north. Samples were not only taken at the same time, but also using the same methods and protocols for optimal comparability. With DNA sequence analysis, the researchers determined which bacteria, protists, phytoplankton and other single-celled organisms were present in the seawater. Also, they predicted microbial interactions and community structures – who eats who? –  with special statistical methods.

Microorganisms dominate marine life

The west Antarctic Peninsula experiences a higher warming rate than the global average and has seen unprecedented heatwaves and losses in sea ice in the past decades, with large regional variability. In the waters around Palmer, the amount of sea ice has decreased more significantly in recent years, as temperatures there have risen faster than off the coast of Rothera. These differing conditions affect microbial community composition, says Engelmann. "At the warmer Palmer site, bacteria affected microbial community structure by interacting with other microorganisms, while at Rothera, it was the other way around. There, microbial eukaryotes were stronger drivers of community structure and dynamics."

Bacteria and microbial eukaryotes play different roles in the marine ecosystem, and the potential shift towards bacterial dominance in warmer conditions could decrease biological productivity. With more bacteria and less phytoplankton, nutrients are more likely to remain in the microbial loop, making them less available for higher organisms like krill, fish, and ultimately mammals and birds. Engelmann: “These findings have significant implications for understanding and predicting microbial ecosystem responses to climate change and are therefore relevant for a broad group of researchers and even for humanity as a whole.”

Measured by their total mass, there are about three times more microorganisms in the oceans than all the marine animals combined. Climate change-induced shifts in the microbial food web of the Southern Ocean will have far-reaching consequences for the global food web, as the Southern Ocean plays a crucial role in producing and recycling organic material that feeds marine life worldwide."

‘There are about three times more microorganisms in the oceans than all the marine animals combined'

Incorporating microorganisms into climate models

Ultimately, Engelmann hopes that microbial community data will find their way to climate and ocean models. “The microbial food web is complex, bacteria and microbial eukaryotes have different functions and there are a lot of interactions among and between these groups, but also with larger organisms including animals. At this point, it is difficult to predict the impact of climate change on microbial productivity. Our research provides crucial baseline data for understanding the complexity of microbial communities in coastal Antarctic ecosystems, but we need more data and a better understanding of marine microbial communities before we can include them in climate and ocean models. But I am convinced that this would make our models much more accurate and could also aid in developing conservation strategies.”

Long-term measurements

The measurements from 2013-2014 are the first thorough analysis of both bacteria and microbial eukaryotes across all seasons in coastal Antarctica. Engelmann hopes that many more measurements will follow. "Now, we've drawn conclusions based on climate differences at two locations. We have samples ready from 2018-2019 and also from 2022. The more of these measurements we collect over time, the more we'll learn about Antarctic marine microbial communities, their interactions and susceptibility to climate change. At the same time, sampling in Antarctica is logistically challenging, laborious and expensive. International cooperation, such as with the British Antarctic Survey and the colleagues in the US who worked at Palmer station and their home universities, is therefore crucial."

Text: Royal Netherlands Institute for Sea Research
Photos: Swan Sow (leadphoto: first author Swan Sow, heading out for seawater sampling from the Rothera long-term ecological monitoring site of the British Antarctic Survey)