Sea urchins threaten Svalbard’s underwater forests

by Rosamaria Kubny

10/27/2026

Dense kelp forests made up of large brown algae provide vital habitats for fish and numerous marine invertebrates. Such underwater forests also grow in the coastal waters of Svalbard. Rising water temperatures and grazing by sea urchins are increasingly altering their living conditions. (Illustration: PolarJournal)

In Kongsfjord on Svalbard, marine researchers are observing significant changes to the underwater world. Unusually high water temperatures and the spread of sea urchins are taking their toll on the Arctic kelp forests. Where dense brown algae once grew, the seabed is now largely bare in places.

Kongsfjord on the west coast of Spitsbergen is increasingly changing in character. According to the Norwegian Institute of Marine Research (Havforskningsinstituttet), its underwater world is becoming ever more similar to that of the northern Norwegian coast. In recent surveys, researchers measured water temperatures at a depth of ten metres that were three to four degrees above normal levels. This followed a marine heatwave lasting around two months that had swept through the region.

Two research divers display brown algae several metres long from the coastal waters of Spitsbergen. The scientists are investigating how the warming of seawater is affecting the Arctic kelp forests. (Photo: Haakon Hop / Norwegian Polar Institute)

Particularly striking is the increasing grazing by sea urchins. These spiny marine creatures feed on kelp, amongst other things, and can graze down large kelp beds when their population density is high. Marine biologist Karen Filbee-Dexter reports on heavily damaged areas where underwater landscapes that are now almost devoid of vegetation have already formed.

However, global warming can also bring benefits for Arctic kelp forests. Less sea ice allows more sunlight to penetrate the water and can promote kelp growth. At the same time, however, living conditions for numerous species are changing. Murkier coastal waters, increasing sediment input and grazing by sea urchins can impair the development of kelp forests.

Numerous sea urchins amongst large brown algae on a rocky seabed. When population densities are high, the animals can graze entire kelp forests bare. Researchers are also investigating the impact of sea urchins on Arctic underwater vegetation in Kongsfjord. (Illustration: PolarJournal)

Kelp forests provide food, shelter and refuge for numerous marine animals. Furthermore, the brown algae sequester carbon as they grow. A widespread loss of these habitats could therefore have significant consequences for the entire coastal ecosystem.

For the researchers, these observations demonstrate just how rapidly the Arctic marine environment is changing. Whether the kelp forests will continue to expand in future due to longer ice-free periods, or whether they will be pushed back by sea urchins, remains to be seen. One thing is certain: an ecological shift is underway beneath the surface of the waters around Svalbard.

Rosamaria Kubny, PolarJournal