Prof. Antje Boetius, Director of the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, speaks about marine microbiomes and global warming.
As a whaler, your grandpa already warned you about future threats to the ocean; as a scientist, you have studied the polar seas and marine microbiomes for more than 30 years. What are the most striking changes related to climate change that you have observed at sea?
Antje Boetius: When we experienced a massive sea ice melt in the Arctic during the summer of 2012, we saw how the networks of life drastically changed. Typically, microbes are invisible to the naked eye, though they colour the ice by forming green and brown biofilms below the surface. We saw how the polar ice changed in colour due to disappearing algae. Colonial sea-ice diatoms, which produce long filaments, and grow during the summer into huge under-ice meadows, melted out and sunk into the deep sea. The ice became white and porous marking the disappearance of microbial life.
The microbiome seems to be a key marker for climate change. How do you assess the marine microbiome’s role in changing the ecological balances in the oceans?
Microbes are at the base of the marine food webs. The photosynthetic ones are primary producers of marine biomass, and the heterotrophic ones are essential in the formation of detritus and nutrient recycling; thus, the ocean microbiome contributes to CO2 drawdown from our atmosphere and to the oceanic carbon storage.
With rising temperatures, it looks like this biological carbon pump gets weaker, as does the physical carbon pump: the process of carrying surface waters loaded with dissolved carbon dioxide to deeper layers where it is isolated from the atmosphere.
Along with sea-ice melting and loss of multiyear ice, specific microbes may even disappear because of the lack of ice. Microbes are the fastest biological markers we have in nature, they are highly responsive to environmental dynamics. Microbiome research is vital because once we understand the links between community composition, biogeochemical functions and environmental dynamics, we can predict what will happen to the ocean’s role as carbon sink.
Also, we have many other questions to answer, for example, to what extent a heatwave changes microbial life and function. There is an increasing body of evidence, that the change of marine single-cell species marks climate change, including consequences for the food webs.
What are the research priorities to learn more about the ocean’s role in climate change and that of its microbiome?
We need to be at the pulse of the ocean to better understand the seas’ current and future productivity, and its resilience. It is essential to learn the feedback mechanisms of the natural microbiome with regard to CO2, or also methane and nitrous oxides, important greenhouse gases in the atmosphere, and for that one needs quantitative information about the distribution of microbial life and its genetic potentials, as well as the biogeochemical rates.
Need for remote sensing tools
The problem is the lack of remote sensing tools. For example, satellite observation of phytoplankton is a great tool; however, it does not work well below clouds and polar ice. There is a need for integrated observation systems, from ships to robots and buoys, measuring essential sets of physical, chemical and biological parameters. As one humanity affected by climate change and ocean functions, we should have measurement nets around the globe, which help us understand chances and threats, but this is not done so far.
There are huge dynamics to assess – think heatwaves in the seas, or oxygen minimum zones and their effects on life. Or take the example of the bleaching coral reefs. We need to address effects on the different biological interactions, symbiotic and pathogenic functions and genetic adaptations of microorganisms, in the context of temperature. How can a switch of temperature turn some microbes into pathogens, or when become algae toxic? We need much more field research, and experiments based on naturally complex communities, because most relevant marine microbes are not cultivated.
A really big problem is the lack of infrastructure and training to address ocean health in many countries. Also we lack international standardisation of some aspects of microbiome research, as addressed in the UN Decade for Sustainable Ocean Science, to better understand the seas.
There is also concern about the health of the seafloor?
Antje Boetius: Yes, especially bottom trawling has already lead to severe impact on seafloor integrity, and destroyed slow growing deep water coral reefs and sponge gardens. A future theme is mineral mining in the deep sea, and its potential to cause long-term losses of biodiversity.
Furthermore, there is pressure on seafloor life by plastic littering, and extraction of minerals. As for the terrestrial soil, we are only understanding now how old these bioactive zones are and how critical for productivity and ecosystem health. We need to come up with better protection of their integrity.
What are the best marine mitigation measures to alleviate climate change?
Antje Boetius: The best mitigation measure is to leave fossil fuels in the ground, and to use wind, sun and wave power instead, to produce regenerative fuels. Everything else is massively expensive and slow.
Nonetheless, the research on nature-based solutions to make the ocean an even better carbon sink is very fascinating and important. Early on, there was much focus on iron fertilisation experiments in nutrient-poor areas to trigger more algal growth, fix the carbon, and sink it to the deep sea. More recent projects work with self-powering pumps to transport nutrient-rich deep-sea water to the surfaces, with the idea to promote algal growth. At the coasts, there are options to restore coastal vegetation with mangroves, sea grass or kelp forests.
Another exciting topic is to enhance the recovery of large plankton feeding whales, of which the excrements are a perfect fertiliser to boost algal growth. Then there are also more technological options like carbon capture and storage in the sea which are explored.
The Consensus Paper of global Microbiologists, to which you have been co-signatory, highlights why the microbiome is not present on the agendas of climate change research. Do you know the reason?
Antje Boetius: Research on the roles of the microbiomes and their feedback with climate change and pollution is still a very young discipline. However, this research might be triggered as we rapidly learn about interactions between microbes, seas, soils, plants, agriculture, and human health. At least we know through the Covid pandemic that we should care more about viruses, bacteria and other microbes out there in nature, forming part of a network of life to which humans belong too.
I have long advocated for a Microbial Observatory for more autonomous marine observation instruments and international research programmes, which is one step – but it is also key to talk and teach about microbes and their many functions for life on Earth.