Norwegian blue forests under pressure

Fish in Norway. © Aleksander Nordahl

Story by
Hartvig C Christie
Senior Scientist, Marine Biologist
Photographs by
Erling Svensen
Underwater Photographer, Author
Photographs by
Aleksander Nordahl
Founder, Executive Editor

Norway’s coastline, including fjords and islands, is more than 100,000 km, covering different regions and more than 13 degrees of latitude (58-71⁰ N) between Sweden and Russia. Blue forests (kelp forests, rockweed, seagrass beds) are abundant along much of this coastline, creating enduring habitats for a huge number of algae and animals across more than 10,000 square kilometres. Unfortunately, in addition to more small-scale physical disturbances, all regions are threatened by larger-scale pressures. When large-scale pressures wipe out much of the blue forests, the remaining forests become more vulnerable and dearer.

Starting with the southernmost region, Skagerrak, eutrophication from agriculture and settlement sources leads to unwanted opportunistic and seasonal algal growth that, additionally favoured by overfishing and increasing temperatures, replace the more persistent blue forests. In particular, the Oslofjord and sheltered bays all along this region is severely affected. Water darkening and other fouling organisms than eutrophication-induced algae are contributing to reduced photosynthesis in this region as also for some coasts northwards.

Filamentous algal growth (a.k.a. "turf") covering seagrass. ©Erling Svensen

Filamentous algal growth covering sugarkelp. ©Janne Gitmark

The south-west coast of the North Sea is also affected by eutrophication, where discharges of nitrogen, phosphorus and organic particles from fish farms are higher than agriculture and sewage pollution. Recent blooms of white sea urchins are reducing the blue forests in this region and can alternate with filamentous algal growth.

You hardly see the kelps underneath the filamentous algae. ©Janne Gitmark

The white sea urchin (Gracilechinus acutus) can form grazing fronts and decimate kelp and other organisms. ©Erling Svensen

In mid-Norway, from the Norwegian Sea coast north to beyond the Arctic Circle, kelp forests grow among islands and in fjords. Here a combination of nutrients causing filamentous or opportunistic algal growth and grazing by green, white or red sea urchins create a patchwork of lost blue forests, most likely from the effects of fish farms and overfishing.

Tangle kelp is under pressure by grazing of green sea urchins. ©Hartvig Christie

Red sea urchins also consume tangle kelp in Norway. ©Aleksander Nordahl

The Northern Norwegian Sea and Barents Sea. This arctic coastline is heavily affected by the grazing of green sea urchins (Strongylocentrotus droebachiensis) except for the very outermost coastline. You hardly see any other animals among the sea urchins. The grazed area cover more than 700 000 football pitches.

Monocultures of green sea urchins create huge underwater deserts. ©Hartvig Christie

Monocultures of green sea urchins create huge underwater deserts. ©Janne Gitmark

So, is there any blue forest left?

The answer is yes! The intertidal seaweeds and most seagrass beds are healthy except for the most sheltered stands. The largest loss is the sugar kelp (Saccharina latissima) forests in sheltered waters and the tangle kelp (Laminaria hyperborea) forests in medium-exposed waters. Along the most exposed coastlines tangle kelp beds thrive as they can tolerate more wave action than filamentous algae and sea urchins. Here we find a lot of small animals and fish. If we treat our coastline in a proper way, we could have more healthy forests.