Finally, the eelgrass is coming back

Since 1900, Denmark has lost 80-90 % of the once lush beds of eelgrass that grew along our shores and in fjords.

This is not only bad for fish and other animals that need the eelgrass as a habitat; it is also bad for the climate, because eelgrass is effective at binding and storing carbon.

On that background, biologists from the University of Southern Denmark decided to investigate whether it is possible to restore eelgrass meadows in Denmark. Their work also has implications for other species of seagrasses, suffering the same fate elsewhere in the world.

Grows like weed

Recently, a research team led by postdoc Troels Lange from the Department of Biology, carried out an experiment with transplanting small, new eelgrass shoots into Horsens Fjord. The results have exceeded all expectations, the team reports in a scientific article in the Marine Ecology Progress Series (link https://doi.org/10.3354/meps13975).

The researchers have transplanted 14,400 small new eelgrass shoots into Horsens Fjord, placed in a 51x78 meter checkered field. After a little more than two years, plant density grew to 70 times higher: approx. 1,005,000 eelgrass shoots. In addition, the fields with transplants have extended by approx. 30 percent, to 1282 square meters against the original 768 square meters.

Transplanting seems to be better than sowing

Given the importance of eelgrass for both biodiversity and carbon storage, several attempts have been made over the years to restore eelgrass beds.

Other researchers have, for example, tried to sow eelgrass; it is a plant that you can sow with seeds just as you sow grass on land. But successes have been limited:

- In such experiments, up to 99.9 % of the seeds have been lost, so today focus has shifted to transplanting, says Troels Lange.

84,000 new shoots in Vejle Fjord

But even that is also a difficult task, he points out:

- If you do not prepare carefully and make sure to choose suitable locations, it will most likely go wrong. We can also see that larger areas with at least 5,000-10,000 transplants have a better chance than smaller areas.

At the moment, the research team is conducting similar experiments in two other places in Vejle Fjord and in Lunkebugten on the island Tåsinge. At the time of writing, 84,000 shoots have been planted in Vejle Fjord, covering an area of 3.42 hectares.