Cloned Baltic Sea eelgrass more sensitive to climate change
In the Baltic Sea, Swedish eelgrass meadows consist of a small number of clones. This worries researchers, as eelgrass with lower genetic variation may find it more difficult to adapt to climate change and other changes in the environment. At the same time, eelgrass is an important nursery for many other species including fish.
“When we tested samples from several eelgrass meadows in the Baltic Sea, we found that the clones differed between meadows, but that individual meadows often consisted of only one clone. Overall, a small number of genotypes dominate in the Baltic Sea,” says Stefanie Ries, who mapped the genetics of Swedish eelgrass in her doctoral thesis.
In addition to cloning, eelgrass reproduces sexually through flowers and seeds, which is much more common on the west coast. There, eelgrass beds also exhibit significantly higher genetic diversity.
“With greater genetic diversity, eelgrass is probably better at adapting to climate change or other changes in the environment,” says Stefanie Ries.
The salinity of the Baltic Sea is significantly lower than that of the west coast. Researchers believe that eelgrass has adapted to an environment where it is more difficult to reproduce sexually.
Cloning as a survival strategy
“Many eelgrass beds in the Baltic Sea are already at the limit of how low the salinity of the water can be for the plant to survive. We actually found flowers on eelgrass at the northernmost collection site in the Baltic Sea, but we don’t know if they produced seeds. And the entire meadow consisted of just one clone,” says Stefanie Ries.
Cloning is a survival strategy for the species, at the cost of a lack of genetic diversity. This probably also means that eelgrass in the Baltic Sea is more vulnerable to changes such as a warmer sea, according to Stefanie Ries.
"And if something were to happen, such as a storm or something else that destroys an eelgrass meadow, it would be very difficult for the cloned eelgrass to recover."
Eelgrass is in decline both nationally and internationally. Climate change is cited as a major cause, but other human impacts such as the exploitation of shallow bays and overfishing also play a role.
Genetics important in restoration
The University of Gothenburg is running a major project to restore eelgrass beds, which are important habitats and nurseries for many other species, not least fish. The Swedish Agency for Marine and Water Management has incorporated Stefanie Ries' research into its work on monitoring genetic diversity in eelgrass beds.
“My research provides a knowledge base that can be used in the continued monitoring of the genetic status of eelgrass and in restoration. For example, if you take plants from one location and move them, there is no guarantee that they will survive, as they are not adapted to their new habitat. You need to understand the genetics in order to create effective and successful measures,” says Stefanie Ries.
Text: Mikael Andersson
Eelgrass is one of a few marine vascular plants and the dominant species of sea grass in Sweden and Norway. The leaves are usually between 30 and 60 cm long, but in some cases can grow as long as 1.5 metres. The plant is perennial and grows on sandy bottoms, usually at depths of between two and six metres.
Eelgrass forms meadows that are very important for the marine ecosystem and serve as nurseries for fish. The large root systems bind bottom sediments, protect against waves and counteract the erosion of sandy beaches. Eelgrass stores carbon, which helps to slow down the greenhouse effect.
Eelgrass reproduces through sexual reproduction or cloning. Cloning is most common in more extreme habitats, at the edge of the species' range. In the Baltic Sea, with its low salinity, there are eelgrass clones that are several hundred years old.
In Sweden, eelgrass is found along the entire coast up to Uppland.
Eelgrass is an endangered species both internationally and nationally, and in Sweden it is red-listed in the vulnerable category.
