Algae revived after 7,000 years beneath the Baltic Sea 

In a breakthrough study, researchers have successfully revived dormant algae that sank to the bottom of the Baltic Sea nearly 7,000 years ago. 

The tiny diatom cells, buried in sediment without light or oxygen for millennia, have regained full biological activity, offering scientists a rare opportunity to study life from the distant past in real time.

The study, led by the Leibniz Institute for Baltic Sea Research Warnemünde (IOW), forms part of the PHYTOARK project, which aims to understand how the Baltic Sea’s ecology has changed over time and what that means for its future.

A time capsule at the bottom of the sea

Many organisms, from bacteria to mammals, can enter a dormant state to survive harsh conditions. For phytoplankton, such as diatoms, dormancy involves forming resistant resting stages that sink and become embedded in underwater sediment. 

These microscopic plants can remain inactive for long periods, preserved in the cold, dark, and oxygen-free conditions of the sea floor.

“Such deposits are like a time capsule containing valuable information about past ecosystems and the inhabiting biological communities, their population development and genetic changes,” said Sarah Bolius, a phytoplankton expert at IOW and lead author of the study. 

By recovering sediment cores from the Eastern Gotland Deep, the research team isolated dormant phytoplankton resting stages from layers representing nearly every major climate phase in the Baltic Sea’s history. 

Using controlled lab conditions with light and nutrients, they successfully “woke up” algae from nine different layers.

Revived algae are thriving

The star of the study was Skeletonema marinoi, a common diatom in the Baltic Sea that thrives during spring algal blooms. This species was the only one that revived from every layer tested, including one estimated to be 6,871 years old.

What surprised the researchers was not only that these algae survived, but that they were biologically thriving. “They grow, divide and photosynthesize like their modern descendants,” Bolius noted. 

Even the ancient samples showed robust growth rates – averaging 0.31 cell divisions per day – and strong photosynthetic activity, with oxygen production levels comparable to today’s S. marinoi strains.

Genetic testing further revealed that the revived algae formed distinct genetic groups based on the age of the sediment they came from. 

This proved not only that the samples had remained isolated from one another, but also that S. marinoi populations in the Baltic Sea had undergone genetic changes over millennia.

Resurrection ecology in action

The approach used in this study falls under the field of “resurrection ecology”- a novel method that allows scientists to revive ancient organisms and study how they have changed over time. 

Until now, similar successes had only been recorded with a few plant seeds and crustaceans. The revived S. marinoi strains are among the oldest living organisms ever reactivated from aquatic sediments.

“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,” Bolius explained. 

“This means that it is now possible to conduct ‘time-jump experiments’ into various stages of Baltic Sea development in the lab.”

Such experiments could help scientists reconstruct past environmental conditions and track long-term evolutionary responses to changes in salinity, temperature, and oxygen levels. 

By linking sediment proxy data – indirect evidence of past climates – with living organisms from those same layers, researchers hope to gain a clearer picture of how species adapt to changing environments.

Revived algae and climate research

At a time when climate change is transforming marine ecosystems, this research offers a rare window into how species may have responded to previous warming and cooling events. 

The ability to study ancient cells alive in the lab, rather than relying on fossils or degraded DNA, opens up entirely new avenues for evolutionary biology and paleoecology.

This study shows that it is possible to directly trace genetic changes over many millennia – by analyzing living cells instead of just fossils or DNA traces. 

Future work will include exposing the revived algae to various environmental conditions to understand how genetic and physiological traits have helped them survive and evolve.

The remarkable resilience of these tiny diatoms underscores not only the adaptability of life but also the value of sediment cores as archives of biological history. 

As Bolius and her colleagues continue to unlock these secrets, their work is poised to shed new light on the intersection of climate, evolution, and the unseen resilience of life beneath the sea.

Image Credit: S. Bolius, IOW

The study is published in the ISME Journal.

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