Photo credits: The Norwegian Institute of Marine Research (IMR).
How kelp and Smart Reefs could help cod return to Porsangerfjorden
By Hans Kristian Strand
The Norwegian Institute of Marine Research (IMR)
Once brimming with cod, the inner reaches of Porsangerfjorden in Northern Norway are today eerily quiet beneath the waves. For decades, overfishing, changing predator-prey dynamics, and loss of habitat have taken a severe toll on local fjord cod populations. Now, as part of the OCEAN CITIZEN project, we at the Institute of Marine Research are helping to lead an ambitious restoration effort grounded in science, local knowledge, and innovative technologies.
Our focus is simple but critical: improving the survival of juvenile cod, especially in their first vulnerable months after hatching. To do this, we are testing whether specially designed artificial reefs—so-called Smart Enhanced Reefs (SERs)—and locally developed KelpReefs can provide the shelter and food that juvenile cod need to thrive.
Why kelp?
Kelp forests are biodiversity hotspots. They offer complex structure and shade, slow down currents, and are home to countless small creatures—ideal conditions for young fish looking to hide from predators and find food.
In Porsangerfjorden, we recently carried out a kelp erosion experiment to better understand how kelp contributes carbon and energy to the ecosystem, particularly as inputs from microscopic phytoplankton decline with the shortening days of autumn. We submerged mesh bags filled with kelp at two depths—10 meters and 50 meters—and monitored how quickly the kelp decomposed during the autumn months. Alongside this, we recorded which species came to feed or take shelter among the decaying kelp. Our findings have been exciting. Not only did the kelp last well into the winter months, but the bags also became magnets for life: snails, shrimps, amphipods, were observed using the decaying kelp as habitat. This gives us strong indications that kelp-covered structures could act as stepping-stones for marine biodiversity—even as they degrade.
Kelp associated fauna in erosion experiment. Photo credits: The Norwegian Institute of Marine Research (IMR).
Testing what attracts young cod and their prey
In another part of the experiment, we set up fine-meshed baited traps at the same two depths—some baited with kelp and some without—to evaluate preferences among local marine fauna.
This kind of data is essential. If structures like SERs and KelpReefs, once installed, become overgrown with kelp, they could effectively transform into miniature kelp forests, creating habitat in places where there was previously little or none. By making these areas more attractive to juvenile cod and their prey, we believe we can tip the survival scales in the right direction.
The broader context: Reviving a lost population
This work is part of a larger, deeply collaborative project to bring life back to the inner parts of Porsangerfjorden. Decades of monitoring and local interviews have shown that spawning grounds and nursery areas in fjord branches like Olderfjorden have all but disappeared. One of the central hypotheses we are testing is whether it’s possible to re-establish a viable spawning population and, crucially, ensure that more young cod survive to adulthood.
We are also planning to set up spawning pens where locally caught cod can reproduce in a controlled setting. The eggs are then released into a prepared environment where the artificial reefs provide improved conditions for the young fish.
Importantly, genetic testing will ensure that we are working with the true local fjord cod population—not migratory “skrei” cod from the Barents Sea—so that the juveniles grow up with the same local adaptations and behaviors that originally evolved in this unique ecosystem.
Hope on the horizon
While it is still early days, our experiments are showing promising results. If successful, this combination of Smart Enhanced Reefs and kelp-based habitat enhancement could offer a model for cod recovery not just in Porsangerfjorden but in many other fjords that have seen similar declines.
By blending technology with ecological insight and working hand-in-hand with the community and international partners, we hope to give cod a real chance to return—one reef, one kelp frond, one juvenile fish at a time.
