When Norwegian researcher Hans Kristian Strand climbed aboard a research boat off northern Norway last May, he expected another disappointing survey. For decades he had watched once-vibrant kelp forests shrink to gray stretches of seabed dominated by hungry sea urchins. Strand and his colleagues had spent 25 years trying to re-establish kelp and the complex habitat it supports, only to see urchin grazers repeatedly undo their work.
Kelp forests fringe about one-third of the world’s coastlines and are foundational to coastal ecosystems. They provide food and shelter for fish and invertebrates, help filter and purify water, sequester carbon and protect shorelines by buffering wave energy. Yet over the past 40 years, northern Norway — home to much of Europe’s kelp — has lost at least 5,000 square kilometers of those marine forests. The decline traces back to the 1950s, when mechanized and intensified fishing reduced populations of predators such as wolffish and haddock. With predators gone, sea urchins multiplied and grazed kelp down to barren ground.
Free diver Karoline Stigum Kvalo, who explores the Lofoten Islands, says the underwater world she now encounters is strikingly different from accounts a few decades ago. Divers once bumped into abundant wolffish in the 1990s; today those fish are almost absent. Kvalo joined a volunteer group called the Kelp Watchers that tried to restore habitat by removing urchins, visiting sites monthly for more than a year—even during winter storms. When urchin numbers fell, many species returned, but the successes proved fragile. A sponge-like seaweed known locally as lurv often colonized cleared areas, blocking light and preventing kelp from reestablishing in spring.
The missing link turned out to be kelp’s reproductive cycle. Kelp grows and blooms in spring, then decomposes in autumn, producing spores that seed the next year’s growth. If kelp is absent in autumn, spores are not produced and nothing returns in spring. That insight led Strand to an idea inspired by forests on land.
Walking among pine trees, he was struck by how conical branches capture and channel sunlight. Working with local seaweed company Polaralge, he and his team harvested sori, the spore-bearing tissue on mature kelp fronds, and put them in tanks to release spores. They mixed the spore-rich water into a thin coating and smeared it onto ropes tied to sand-filled plastic rings, creating suspended, climbable structures that could intercept light when deployed underwater.
In February the team installed these artificial reefs and left them exposed to available light. When they returned in spring, the ropes were cloaked in young kelp that sea urchins could not easily reach. Earlier restoration designs had failed, so finding these structures abundantly colonized was an unexpected breakthrough.
To date, the project has deployed 17 of these reefs along the northern Norwegian coast and plans to scale up to as many as 1,000 units built from black plastic piping filled with sand. The team has looked for alternatives to plastic but says nothing yet matches the ease of construction and transport needed for wider use.
Restoration is urgent: kelp is under pressure from warming seas, pollution and overfishing. Research by the nonprofit One Earth estimates global kelp forests have declined by 40–60 percent over the past half century, with some places—parts of southern Australia and northern California—losing up to 95 percent of giant and bull kelp.
Strand hopes the artificial reefs can offer a durable way to revive kelp habitats; researchers from the Baltic region have already expressed interest. The Kelp Watchers have paused their urchin-removal efforts while the reef approach is tested. For divers like Kvalo, the return of kelp has transformed her experience: where she once saw only barrens, she now notices tiny communities on a single kelp leaf and the richer diversity kelp supports. If scaled successfully, the approach could help rebuild the coastal forests that undergird so many marine communities.