Sugar kelp forests on the directorates’ rescue list

| March 1st, 2023 | Highlights

SUGAR KELP FORESTS ON THE DIRECTORATES’ RESCUE LIST

By Trine Bekkby, Eli Rinde, and Hege Gundersen – Norwegian Institute for Water Research (NIVA)

Sugar kelp forests along the Norwegian coast are important habitats for a large number of species and contribute many ecosystem services, such as food,  raw materials, and carbon sequestration. Sugar kelp forests are considered highly threatened, most likely due to increased temperatures and deposits of nutrients, particles, and humus. A directorate group led by the Norwegian Environment Agency is now proposing to include southern sugar kelp forests into the Follow-up Plan for Endangered Nature (Oppfølgingsplanen for trua natur), with the aim of assessing what measures we can take to reduce these threats by 2035.

Sugar kelp forest outside of Bergen, NIVA

A directorate group led by the Norwegian Environment Agency is now proposing to include southern sugar kelp forests in the Follow-up Plan for Threatened Nature (Oppfølgingsplanen for trua natur). In order to protect the most vulnerable nature, as has been agreed in the UN’s new nature agreement (the Kunming-Montreal agreement), the importance of nature must be taken into account by all sectors. The aim of the follow-up plan is to assess what measures can be taken to reduce these threats by 2035.

Sugar kelp grows along the entire Norwegian coast, including Svalbard. It can become 1-3 meters long and forms forests that function as habitats for animals and algae down to 20-30 meters deep in relatively wave-protected coastal areas. Kelp forests are important habitats for a large number of species of algae and animals, and contribute ecosystem services such as food and raw materials. They are also thought to have an important role with regard to climate adaptation and mitigation through carbon sequestration.

Our sugar kelp forests are considered highly threatened by the Norwegian Red List for Habitat Types. They are also on OSPAR’s list for threatened nature. Norway therefore has international commitments related to sugar kelp forests, and they are included within the Environment Agency’s proposal for habitat types to be prioritised for mapping according to criteria given in Parliamentary Announcement no. 14 (2015-2016) – Nature for life. Southern sugar kelp forests can be found in the North Sea and the Skagerrak strait. Here, sugar kelp forests have been in decline since the 1990s, most likely due to increased temperatures and deposits of nutrients, particles, and humus. Increased run-off from land, as well as deposits of humus and particles, generally contribute to darkening the coastal waters and thereby reducing the growth depth of kelp and other bottom-dwelling algae. The growth and recruitment of sugar kelp are negatively affected by each of these factors. Indeed, large areas of kelp forests have gone from being productive zones with perennial species of seaweed and kelp and high biological diversity to being dominated by opportunistic filamentous algae. The most loss of kelp forest has been in the Skagerrak, but it has also been significant in the North Sea.

Janne Gitmark, NIVA

There is a danger that the situation will worsen if nothing is done about the sources of these inputs to the sea.

The consequence of sugar kelp disappearing is that algae and animals lose their habitats, which can be spawning grounds, nursing areas or, as for the coastal cod, feeding grounds. Imbalance in the ecosystems reinforces the overfertilization effect and creates ecosystems that are less robust. Such areas become more vulnerable to the loss of sugar kelp forests and to the invasion of alien species, such as Sargassum muticum and Dasysiphonia japonica which can displace local species.

There is a danger that the situation will worsen if nothing is done about the sources of these inputs to the sea. In the Skagerrak, the most important sources of nutrients are runoff from agriculture and sewage. In Western Norway, fish farming is among the most significant of anthropological sources. The inclusion of sugar kelp forests in the Follow-up Plan for Endangered Nature is an important step towards bringing back this valuable habitat.

Relevant literature:

Aalberg Haugen m. fl. 2019. Tiltak for å ta vare på truet natur: Kunnskapsgrunnlag for 90 truete arter og 33 truete naturtyper. NINA-rapport 1646.

Bekkby m. fl. 2021, Forslag til forvaltningsrelevante marine naturenheter. NIVA-rapport 7672, 40s.

Bekkby m. fl.. 2022. Forslag til variabler for økologisk kvalitet for lokaliteter av forvaltningsrelevant marin natur. NIVA-rapport 7797-2022 (M-2430|2022), 116 ps + vedlegg

Convention on Biological Diversity. 2023. Kunming-Montreal Global Biodiversity Framework.

Christie m. fl. 2019. Shifts between sugar kelp and turf algae in Norway: regime shifts or flips between different opportunistic seaweed species? Frontiers in Marine Science 6.

Gundersen m. fl. 2018. Sukkertareskog i Nordsjøen og Skagerrak, Marint gruntvann. Norsk rødliste for naturtyper 2018. Artsdatabanken, Trondheim.

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