Eelgrass restoration in NW Sweden: Lessons learned

Per-Olav Moksnes1, Eduardo Infantes1, Louise Eriander1
1 Department of Marine Sciences, University of Gothenburg, Sweden

Along the Swedish northwest coast, more than 60% (approximately 12 500 ha) of the eelgrass has vanished since the
1980s as a result of nutrient pollution and overfishing. Although measures have improved the water quality in recent
years, no natural recovery of eelgrass has occurred. Instead the losses of eelgrass continue as a result of coastal
exploitation and local regime shifts1. Restoration of eelgrass constitutes a potential tool to recreate historic habitats
and to mitigate eelgrass meadows that are destroyed during exploitation.
Since 2010, extensive studies have been carried out to develop and assess methods for large-scale restoration of
eelgrass in Swedish waters. This effort has resulted in a detailed technical handbook2 and video guidelines3 that
includes all important steps in the restoration process, from site selection and permit processes to harvest and
planting of eelgrass, and monitoring and evaluation of results.
For eelgrass restoration in Sweden, the single-shoot method is recommended where single, adult shoots are harvested
and planted by hand, without sediment or anchoring, using diving. The harvest method does not result in any
measurable impact on the donor meadows, and the planting methods are relatively fast. Studies suggest that 4 divers
could harvest and plant 40 000 shoot in 10 working days, and that the shoot density can increase 10 times before the
winter during optimal conditions. Seed-methods for eelgrass restoration have also been developed for Swedish
conditions, but cannot presently be recommended due to very high and variable losses of seeds, mainly due to seed
predation4,5.
Monitoring and evaluating of the environmental conditions at a potential site constitute a critical first step in the
restoration process. When an eelgrass meadow is lost, the environment may change so much that it no longer allows
eelgrass growth. In NW Sweden, test planting failed in over 90% of evaluated sites, mainly due to poor water quality
resulting from local sediment resuspension, but also because of shading from algal mats and disturbance from shore
crabs and geese1. In Sweden it is recommended that eelgrass restoration should only be attempted at sites where testplanted
shoots show positive growth after one year.
At present the recommended restoration methods are being applied in several medium to large scale projects (0.1-1.0
ha) along the Swedish west coast and in the Baltic Sea. Diving consultants have harvested and planted up to 80 000
eelgrass shoots in two months to a cost of approximately €130,000 per hectare. Preliminary results show variable
success. Presently, news methods using sand capping to improve environmental conditions for eelgrass are being
developed and evaluated.
Although functional methods for eelgrass restoration are available for Swedish waters it is important to note the
eelgrass restoration is very labor intensive, expensive and the results are many times uncertain. Also in areas with
apparent good environmental conditions, a storm or a heat wave can result in unsuccessful restoration. In addition,
hand planting using diving limits the scale of projects to a few hectares per year, which is a very small amount in
comparison with the 1000s of hectares that has been lost in Sweden. Thus, the available restoration methods can
likely not alone recreate the historic distribution of eelgrass. Hence, it is imperative that environmental managers
prioritize the protection and conservation of remaining eelgrass habitats. Still, in combination with large-scale
measures that improves the conditions for eelgrass growth, restoration at strategically chosen locations may
constitute an important complement that could enable and accelerate natural recovery of Swedish eelgrass habitats.

References
1. Moksnes P-O, Eriander L, Infantes E, Holmer M. 2018. Local regime shifts prevent natural recovery and restoration of lost
eelgrass beds along the Swedish west coast. Estuaries and Coasts. 41:1712–1731. DOI: 10.1007/s12237-018-0382-y
2. Moksnes PO, Gipperth L, Eriander L, Laas K, Cole S, Infantes E. 2021. Handbook for restoration of eelgrass in Sweden -
National guideline. Swedish Agency for Marine and Water Management, Report number 2021:5. 146 pages
3. https://www.youtube.com/channel/UCPx0jz3gl8VN4Nd8QlBOYLQ
4. Eriander L, Infantes E, Olofsson M, Olsen JL, Moksnes P-O 2016. Assessing methods for restoration of eelgrass (Zostera marina
L.) in a cold temperate region. Journal of Experimental Marine Biology Ecology. 479:76-88. DOI:10.1016/j.jembe.2016.03.005.
5. Infantes E, Eriander L, Moksnes P-O. 2016. Eelgrass (Zostera marina L.) restoration on the west coast of Sweden using seeds.

Marine Ecology Progress Series. 546:31-45. DOI: 10.3354/meps11615