Scientists have managed to revive microscopic algae that had been lying dormant for nearly 7,000 years at the bottom of the Baltic Sea. Once reactivated, these organisms did not just survive. These tiny organisms at the base of marine food chains, called Phytoplankton, have a survival trick. When conditions turn bad, they go dormant and sink. In places like the Baltic Sea, where deep sediments lack oxygen, these cells can remain preserved for thousands of years.
The work was led bySarah Bolius at the Leibniz Institute for Baltic Sea Research (IOW). As reported in the study published in The ISME Journal, sediment cores from the Eastern Gotland Deep hold a layered archive of past environments, making it possible to match living organisms with specific periods in history.
Deep-sea Mud Acts Like A Natural Archive
The samples came from 240 meters below the surface, collected during a 2021 expedition aboard the Elisabeth Mann Borgese. Each layer of sediment corresponds to a different moment in the Baltic Sea’s past. As explained by the researchers, these layers also contain clues such as salinity and oxygen levels that help reconstruct past conditions. Boliusstated that:
“Such deposits are like a time capsule containing valuable information about past ecosystems and the inhabiting biological communities, their population development and genetic changes.”
Scientists Wake Up Algae Using Light And Nutrients
As explained by latest research, published inISME Journal, to bring the algae back, the team used a method called resurrection ecology. They provided dormant cells with light and nutrients and observed whether they would reactivate.
“Dormancy is a widespread key life history trait observed across the tree of life. Many plankton species form dormant cell stages that accumulate in aquatic sediments and, under anoxic conditions, form chronological records of past species and population dynamics under changing environmental conditions,” explained the team of the study.
It worked. The diatom Skeletonema marinoi, still common in the Baltic sea today, was revived from all the sampled layers. The oldest cells approached 6,900 years, yet only one species repeatedly managed to revive.
“The fact that we were actually able to successfully reactivate such old algae from dormancy is an important first step in the further development of the ‘Resurrection Ecology’ tool in the Baltic Sea.” She added, “this means that it is now possible to conduct ‘time-jump experiments’ into various stages of Baltic Sea development in the lab.”
Ancient Algae Behave Like Modern Ones
What stands out is how normal these ancient cells seem. Once revived, they started dividing and producing energy just like present-day algae. Growth rates averaged around 0.31 divisions per day, and photosynthesis measurements reached about 184 micromoles of oxygen per milligram of chlorophyll per hour. According to the researchers, those numbers match modern S. marinoi.
“For the future, sediment archives, together with the resurrection approach, would offer a powerful tool to trace adaptive traits over millennia under distinct climatic conditions and elucidate the underlying mechanisms,” the authors wrote.
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