Study: Oldest known marine plant lives in the Baltic Sea

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The oldest marine plant known to date lives in the Baltic Sea: The seagrass clone that researchers have found with the help of a new genetic clock is 1402 years old, the GEOMAR Helmholtz Center for Ocean Research Kiel has announced.

For the first time, scientists have been able to precisely determine the age of a large marine plant clone. To achieve this, they examined the gene sequences. "Undirected, random mutations in the genetic information, which occur as regularly over time as clocks tick, play an important role here", said the team, which published its findings in the journal Nature Ecology and Evolution.

Seagrass outperforms Greenland shark and Arctic Island clam

In principle, seagrass is capable of sexual reproduction via flowers and seeds, but also via rhizomes (shoot axes) in the sediment – i.e., asexual, also known as clonal reproduction. Plant clones branch out or form buds. This results in a genetically similar offspring that can grow larger than a soccer pitch, the researchers explained. The plant therefore always develops new shoots, but these go back to the same original shoot. However, the clones are not completely identical: so-called somatic mutations that have arisen in the course of the plant's life accumulate in the offspring. The research team compares this to tumor growth. The team took advantage of this and developed a molecular clock that could determine the age of the clones very precisely.

The great seaweed (Zostera marina) is found from the Pacific to the Atlantic and Mediterranean. The researchers were able to trace the origins of the oldest seagrass plant back 1402 years. "This clone reached this advanced age despite a harsh and changeable environment," writes the team. "The seagrass clone thus surpasses the age of the Greenland shark or the Arctic Island mussel, which only live for a few hundred years." However, the investigations also clarified that the size of a clone does not necessarily indicate its age.

"A prerequisite for solving a long-standing puzzle of evolutionary biology"

With the genetic clock used by the team, the researchers could now find out how old other clones are. "Such data are in turn a prerequisite for solving one of the long-standing puzzles of evolutionary biology, namely why such large clones can exist at all despite variable and dynamic environments", says Thorsten Reusch, Professor of Marine Ecology at the GEOMAR Helmholtz Center for Ocean Research Kiel. The research approaches could also help to find better protection for corals.

The team used a high-quality seagrass genome for the study. In addition, part of the international team had kept a seagrass clone in culture tanks for 17 years. This served as a reference value.

Team wants to find the oldest organisms on Earth

"We expect that other seagrass species and their clones of the genus Posidonia (Neptune grass) in the Mediterranean and off the Australian coast, whose distribution extends over more than ten kilometers, have much higher age values and are therefore by far the oldest organisms on Earth", says Reusch.

The international research team from Kiel, London, Oldenburg and Davis, California, was led by Thorsten Reusch (GEOMAR Helmholtz Centre for Ocean Research Kiel), Benjamin Werner (Queen Mary University London) and Iliana Baums (Professor at the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg).

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