Scientists bring marine plankton back to life to study past climate change
Phytoplankton such as are responsible for half the global primary production (GPP), and some form resting cysts that can lie dormant in marine sediments for up to a century. Earlier this year, scientists succeeded in making use of these cellular time-capsules to understand changing ocean conditions in a Swedish fjord.
A team of scientists from Denmark and Sweden revived 193 clonal strains of dinoflagellate (Pentapharsodinium dalei) from cysts in sediments cores taken from Koljö fjord in Sweden, spanning 9 decades. Using DNA microsatellite analysis they reconstructed the population genetics of cysts from older sediments (1922 – 1960), sediments in the middle of the core (1960 – 1985), and from the newest sediments (1985 – 2006). They found two sub-populations that alternated in frequency during the study period.
One sub-population started out common, but became much rarer between 1960 and 1985, and experienced a population revival in the most recent sediments. The authors say these changes are closely linked to natural global climate oscillations. The oldest and the most recent sediments were both formed during summer phases of the (NAO), which impacts temperature and salinity in Koljö fjord. One sub-population prefers cooler, saltier waters while the other thrives in warmer, more dilute seas.
Dinoflagellates like P. dalei are important indicator species, reacting quickly to changes in temperatures. The majority of previous studies on the genetic structure of aquatic protist populations have been short-term, failing to capture multi-decade dynamics that reveal the effects of climate change. But this study offers a rare, multi-decade baseline of natural changes in phytoplankton abundance and species composition, vital for future comparison studies looking at modern changes due to human-driven climate changes.
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