Why did the European oyster disappear from the North Sea?
For the first time, an interdisciplinary research team decodes the historical genetic diversity of the European oyster with the aid of museum collections.
Around 150 years ago, the European oyster Ostrea edulis was still a common delicacy on the European coast. Since then it has become at risk of extinction and has not been seen in the North Sea since the 1930s. Until now industrial overfishing has been assumed to be the reason for this. Researchers from the Zoological Museum and the Institute of Clinical Molecular Biology (at Kiel University, however, assume its extinction in the North Sea is due to the fact that this species of oyster adapted so well to the extreme living conditions in the Wadden Sea that it was no longer able to react to external changes. This is suggested by DNA analyses of oyster shells, which the researchers have used to prove for the first time the historical distribution and genetic diversity of the European oyster. The study, which was recently published in the journal Scientific Reports, is based on the unique collection of oyster shells at the Zoological Museum in Kiel. The findings could also be of significance to the current programme of re-establishing the European oyster.
The European oyster was fished in abundance and eaten with gusto and therefore a major economic factor for the northern German region in the 19th century. In 1868, with the aim of boosting its population in the shallow coastal waters, the Prussian government commissioned a detailed study of the mollusc species led by Karl August Möbius, Professor of Zoology in Kiel. For this purpose, Möbius created an extensive collection of oyster shells, which contained around a thousand specimens from the North Sea, from along the Atlantic coast, and from the Mediterranean. With his investigations into how oysters develop in mutual dependence on other animals and plants in their habitat, Möbius became a founding father of modern ecology.
The new study emphasizes the importance of Möbius’ oyster collection for current biodiversity research. “The carefully documented collection offers unique research material, especially for modern scientific methods,” stressed Dr Dirk Brandis, Director of the Zoological Museum and lecturer at Kiel University. It was one of the first museums ever to examine historical collections with regard to their genetic information. „Thanks to proper storage, the extensive material and the experience of the IKMB, with whom we collaborated on the genetic analysis, we were able to trace the relationships of the European oyster,“ says marine biologist Sarah Hayer, first author of the study and a doctoral student at Brandis at the Zoological Museum.
Surprising regional differences in the genetic material
“This type of historical sequencing involves a lot of effort because a large amount of the historical DNA decomposes over the years. With these oyster shells, however, we were able to achieve amazingly good results,” said Professor Ben Krause-Kyora, Director of the Ancient DNA Laboratory at the IKMB. The research team was surprised at how different the oysters from individual regions were genetically. “Because normally the sea current in coastal regions enables exchange between populations and so their genetic structure ought to be relatively similar,” said marine population geneticist Dr Christine Ewers-Saucedo from the Zoological Museum, who is leading the study.
According to one finding from the study, the oyster specimens from the Wadden Sea were genetically significantly different from those in other areas. The research team regarded this as an indication of how well the European oyster adapted over the course of time to the extreme living conditions in the Wadden Sea with its heavily fluctuating water levels, temperatures, and salt contents. But this appears to have been the cause of its downfall, too, they assume. It seems it was no longer able to adapt flexibly to climatic changes and novel pathogens and finally died out in the Wadden Sea, accelerated by the heavy overfishing in the 1930s. “This also explains why later attempts at establishing a population there from other areas of Europe were not successful – these oysters did not have the right genetic requirements,” said Ewers-Saucedo.
Taking genetic factors into consideration in current re-establishment projects
Möbius‘ oyster collection not only enables extraordinary insight into the past but also provides new findings for current re-establishment projects. “Oyster beds offer unique habitats and they secure loose sediment or slow the current,” said Ewers-Saucedo, highlighting the importance of oysters for marine ecosystems. The research team recommends that if the European oyster is to be re-established in the Wadden Sea, genetic factors need to be considered too.
“With the decoding of the genetic diversity of the European oyster, this study also demonstrates the unique scientific value of the museum’s natural history collections,” said Brandis. He and the team at the Zoological Museum are currently preparing an exhibition to show how museums are conducting research with the aid of their collections. This will also include examples from Möbius’ oyster collection.
The study was supported by the Cluster of Excellence ROOTS “Social, Environmental, and Cultural Connectivity in Past Societies” from Kiel, funded by the German Research Foundation (DFG). It was developed within the framework of the research project “Historical collections of marine organisms – a window into the beginnings of Global Change in the North and Baltic Seas”, which was funded by the Federal Ministry of Education and Research. Alongside Kiel University’s Zoological Museum and the Ancient DNA Laboratory, Senckenberg – Leibniz Institution for Biodiversity and Earth System Research (SGN), the German Primate Center and the Verbund der deutschen Nord- und Ostseesammlungen (NORe e.V.) (association of German North Sea and Baltic Sea collections) are also involved in the joint project.
Photos are available for download at:
Caption: Historical oyster shells from the collection at the Zoological Museum in Kiel, created between 1868 and 1885 by the natural scientist Karl August Möbius.
© Zoological Museum Kiel
Caption: In the clean room at the IKMB, Sarah Hayer, a PhD student in marine biology, prepares oyster shells up to 150 years old for genetic analysis.
© Ben Krause-Kyora
Bildunterschrift: Unterwasserbilder der letzten einheimischen Austernbänke in der Bretagne, Frankreich.
© Stephane Pouvreau (2017). Ifremer. https://doi.org/10.24351/48842
PD Dr. Dirk Brandis
Head of Zoological Museum of Kiel
Hayer, S., Brandis, D., Immel, A., Susat, J., Montserrat Torres-Oliva, M., Ewers-Saucedo, C., Krause-Kyora, Ben et al. Phylogeography in an “oyster” shell provides first insights into the genetic structure of an extinct Ostrea edulis population. Sci Rep 11, 2307 (2021). https://doi.org/10.1038/s41598-021-82020-x
https://www.uni-kiel.de/en/025-oyster - link to the press release
https://www.uni-kiel.de/de/universitaet/detailansicht/news/365-austernsterben Read more about how the researchers ruled out the American slipper limpet as the cause of the oyster mortality, recently.