Microbial communities in the colder polar seas north and south of the 60th latitude feature fewer species and are genetically less diverse. This makes it harder for these communities to adapt to higher water temperatures. “Our findings indicate that they could be more specifically adapted to their particular niche environment. As a result, they may be less able to adapt their metabolic processes to warmer water temperatures, such as those that will arise in polar waters as climate change develops,” says Sunagawa. For this reason, microbes from cold waters could eventually be displaced by the competition from warmer oceans.
This idea is supported by the second study, which was also published in
Cell
today and for which Sunagawa and his scientific staff member Guillem Salazar were co-authors. In this study, researchers led by Lucie Zinger and Chris Bowler from CNRS and ENS, Paris, investigated the worldwide diversity and distribution of various major planktonic groups, including viruses, single-cell eukaryotes and animal matter.
They show that although plankton lives in a continuous ecosystem, it is unevenly distributed. The highest biodiversity can be found in non-polar seas, and variety decreases towards the poles.
Climate warming changes composition
This decrease coincides with abrupt changes in the chemical and physical conditions of surface waters, which in turn lead to changes in the composition and amount of microbial communities in these three areas. “Here, too, temperature is the key factor that controls the biodiversity of plankton communities,” says Zinger. Northern seas are important fishing grounds: they rely on the current state of plankton, which is the basis of all marine food webs. If the composition of the plankton changes, the food resources for fish and other higher marine life, and thus also for humans, could change massively.
The consequences of global ocean warming are currently not predictable, particularly in the polar regions. However, Sunagawa believes that they will be negative rather than positive, and stresses that the environmental impact of other temperature-dependent factors, such as oxygen depletion and ocean acidification, need to be better understood. As a researcher of data-intensive analyses, he therefore advocates for long-term, interdisciplinary ocean observation projects.
The research consortium’s studies are based on several expeditions conducted by the Tara Ocean Foundation between 2009 and 2013. These involved more than 120 researchers who gathered plankton samples from surface waters and from water depths down to 1,000 metres across 210 locations along various transects in all oceans. The aim of the expeditions was to investigate planktonic ecosystems in the context of climate change.