Eelgrass disease along the Norwegian coast

Eelgrasses (Zostera spp.) are perennial, flowering plants that grow at sea. They create large meadows which are important ecosystems and habitats for many marine species. Eelgrass is common along the entire Norwegian coastline but unfortunately we are seeing a global trend of reduced eel grass populations.

Since 2018 Venche Talgø and colleagues have detected several possible pathogenic species of Phytophthora and Halophytophthora in eelgrass along the Norwegian coast. It is uncertain how many of these species contribute to the decline in eelgrass, but further research is needed.

Because Phytophthora and related species often cause severe disease in terrestrial plants, there is reason to suspect that it is these species that are causing the diseases we are seeing in eelgrass along the Norwegian coast. The diseases manifest as dark spots with dead tissue on the foliage and decay in the roots.

Isolates from diseased eelgrass have been cultivated and the species identified using DNA analyses at NIBIO. Two Halophytophthora species and three Phytophthora species have now been found, four of the species were not previously detected in Norway.

To prove how harmful the isolated species are to eelgrass, infection tests must be performed on healthy plants. In the Netherlands, Sweden and Denmark, eelgrass was found to have been infected by Phytophthora, so infection testing could not be carried out.

“We know a location in Vestlandet with an apparently healthy eelgrass population,” explains Talgø. We are hoping that we can use seeds or plants from there in infection testing, provided that the resources are available. Extended mapping to establish the disease status of eelgrass in Norway should be performed.