Scientific diving in Arctic kelp forests to detect climate-related changes

The Arctic tundra has no trees, but lush underwater kelp forests are present from the water surface down to 15–25 m, where low light limits growth. In 2024, the BlueARC project conducted a scientific diving campaign to study kelp forests in Kongsfjorden, revisiting locations sampled 26 years ago.

Kelp forests are important to coastal ecosystems, where they support unique biodiversity and contribute considerably to the carbon budget in glacial fjords, such as Kongsfjorden in Svalbard. The BlueARC project aims to put Norway at the forefront of research and understanding of how climate change affects kelp forests in northern areas. 

Marine vegetation along Arctic coasts is expanding in some areas because climate warming is driving longer open-water seasons and less ice scouring. Many surveyed sites around the Arctic have seen increases in abundance, biomass and species richness, including expansion of distribution ranges. In Svalbard, the most notable change involves a large increase in macroalgal biomass in the upper subtidal zone because of less ice scouring from landfast sea ice, but also less biomass at depth because of darkening of the water.

The dominant macroalgal group in Arctic waters are the brown seaweeds, especially the large oarweed (Laminaria digitata), winged kelp (Alaria esculenta) and sugar kelp (Saccharina latissima), which can grow several metres long and support high biodiversity. They typically start to grow in late winter when solar irradiation is low, but nutrient levels are high before the phytoplankton blooms start in early May. Kelp forests serve as important foundation species and are major primary producers on rocky shores. In Kongsfjorden, their annual production may be in a range similar to that of phytoplankton.

In Kongsfjorden, seaweeds have expanded and increased in biomass in some areas since our first dive surveys in 1996/98, when landfast sea ice was still widely present in the fjord. The largest changes have occurred in the shallows (2.5 m depth), where one of our study sites, Hansneset, has seen 7-8-fold increases in kelp biomass since the early survey and have supported a standing biomass in the range of 11-14 kg fresh weight per square metre during 2012-2021. Such high biomass is similar to that of healthy kelp forests in mainland Norway. The kelp community also changed, with increased dominance of winged kelp down to 10 m depth, while oarweed and sugar kelp retreated to the shallows at 2.5 m. 

Climate warming has also meant more run-off from land, because of increased precipitation and thawing of permafrost and glaciers. This has resulted in increased turbidity from expanding sediment plumes, limiting the amount light at depth. Thus, at depths below 10 m, large brown algae have largely vanished, except for a few individuals of winged kelp. What remains are mostly red algae, which can persist at low light levels down to at least 40 m depth.

Along the coast of northern Norway, sea urchins have grazed down entire kelp forests; for example, sugar kelp has disappeared from the Tromsø area. Grazing by sea urchins is less apparent in Svalbard and is only patchily documented. However, hordes of sea urchins were observed in the outer part of Kongsfjorden in May 2024, which suggests that these grazers could spread farther into the fjord with rising temperature and better growth conditions. 

Svalbard’s coastal zone is changing rapidly with climate change, and scientific diving-based research projects are essential to understand the consequences of these changes for Norway’s unique High Arctic marine ecosystem! This kelp research in Kongsfjorden is part of a larger pan-Arctic study, The impact of climate change on Arctic blue carbon (BlueARC), led by Karen Filbee-Dexter at the Institute of Marine Research.

This project aims to determine how efficient Arctic kelps are at fixing and storing carbon as they grow and what happens to this carbon after the kelps dismantle seasonally and become buried in the sediments, constituting a carbon sink. This is put into a climate-change perspective with increased stores of “blue carbon” because of increased kelp biomass in shallow waters and, thus, increased carbon sequestration at low temperatures and slow decay process.

Acknowledgements

The BlueARC research project is funded by the Research Council of Norway (334760) and Arctic Field Grant (RIS 12373). The Norwegian Polar Institute supports the project logistically. We thank Luisa Düsedau for reuse of her published figures in an open access journal (with rights granted), and Anca Cristea (Norwegian Polar Institute) for providing the Sentinel image.