Eelgrass disease along the Norwegian coast

Eelgrasses (Zostera spp.) are perennial, flowering plants that grow on the soft seabed along the coast. They form 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 of eelgrass, and further research is needed.

Because Phytophthora and related species often cause severe diseases in terrestrial plants, there is reason to suspect that these species 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 of 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, and four of these species were previously not detected in Norway.

To prove that the isolated species are harmful to eelgrass, infection tests must be performed on healthy plants. In the Netherlands, Sweden and Denmark, where similar Phytophthora species have been detected, it has not been possible to find healthy eelgrass for such tests to be carried out.

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