The latest field evidence from Norway’s Institute of Marine Research shows that although kelp biomass in southern Nordland generally returns to previous levels five years after harvest, the epiphyte–rich community and associated biodiversity takes closer to eight years to recover, contrasting with current practices across most of Norway. The 2025 publication adds important field–scale stock and extraction estimates, clarifies how kelp respond in the first year after harvest, and outlines method improvements for acoustic biomass estimation.
A Simple Question With Large Implications
When commercial kelp harvesting began in southern Nordland in 2022, scientists wanted to know whether the forests of Laminaria hyperborea would recover quickly enough to keep ecosystems healthy and the kelp industry viable. The Institute of Marine Research (short: IMR) designed a multi-year monitoring programme that combined legacy trial-harvest stations with a full network of transects across every harvest field from Bindal to the southern edge of the Vega archipelago. The report (published on 28 October 2025) distils the story of 2020 to 2024 into a clear answer. Canopy size and biomass return to reference levels roughly five years after harvesting, while the epiphyte communities that importantly turn a stand into a complex habitat take about eight years to reestablish compared to undisturbed forest areas.
This difference is not a contradiction. It reflects two clocks that tick at different speeds.
Biomass can grow back quickly, which suits a reliable supply chain. Habitat complexity recovers more slowly, which matters for ecosystem health, biodiversity and fisheries that use kelp forests as nurseries, which are also crucial food sources for important and protected seabirds in the area. Nordland’s harvest rotation deliberately mixes five-year and ten-year cycles so it can trial and assess different recovery periods, and this report evidences why that is important for establishing best practices in the industry.
How The Monitoring Works
IMR’s approach uses three complementary lines of evidence to monitor recovery. Underwater video transects measure cover, height and density of kelp each June, ensuring comparability across years. Targeted sampling enables the biomass, ages and epiphyte cover of kelps to be determined and records the presence of juvenile sea urchins in the holdfasts. Vessel-mounted acoustics convert echo intensity into large-scale biomass estimates of the forests that can be repeated efficiently across many stations and seasons. Together, these methods turn snapshots into a more complete picture of recovery.
The acoustic element is particularly important because it scales the work beyond what divers or video alone can do, allowing wider areas of kelp forests to be assessed. IMR’s peer reviewed method shows how standard fisheries echosounders can be calibrated against ground truth video so that echograms become robust point estimates and, ultimately, spatial maps of kelp biomass. That makes annual, coastwide accounting feasible with gear that many vessels already carry.
How Norwegian Kelp Forests Recover After Harvesting
The transects run each June, show fresh trawl tracks in fields harvested in the previous summer, followed by recolonisation of kelps. One year after harvesting, kelp coverage is often high, although the canopy height is still low. In several fields harvested in 2023, the open patches also hosted another opportunistic and non-commercial kelp species, Saccorhiza polyschides, that colonises spaces after disturbance, highlighting the potential for harvesting to shift species assemblages. These pulses may be transient stages rather than regime shifts, as Laminaria hyperborea was observed to regain dominance in the second year, nevertheless, it is unclear whether this will happen after repeated harvesting over multiple years.
Sea urchin abundance remains critical to assess given their role in devastating kelp forest losses recorded in much of northern Norway, threatening both biodiversity and the kelp industry. Fortunately, moderate densities of red sea urchin , Echinus esculentus, were recorded in the Nordland surveys, and although juveniles of the green sea urchin Strongylocentrotus droebachiensis were found in holdfasts, there was no sign that grazing prevented recolonisation in harvested lanes during 2022 to 2024. IMR therefore calls for continued surveillance while noting that current levels did not impede recovery.
A five-year kelp biomass and eight-year biodiversity recovery pattern has been reported previously in Norway. The 2025 report reaffirms these timescales across many more sites in a new area of Norway, highlighting a clear trend with important sustainability implications across Norway. It also introduces higher resolution stock and extraction estimates which are needed for regulatory bodies, such as the Directorate of Fisheries.
Improvements In Stock Estimates With Acoustic Modelling
One of the most significant outcomes from IMR’s work has been to create a field scale biomass model. Built on a 50 meter grid, it accounts for depth, wave climate and bottom type and handles spatial autocorrelation explicitly, turning transect observations into maps of standing stock and uncertainty for the entire harvest area. The model estimates about 579000 tonnes of Laminaria hyperborea across all depths in southern Nordland, with approximately 516000 tonnes in the legally harvestable band between two and twenty metres. These numbers allow a direct comparison to reported landings in 2022 to 2024, which translates to an overall extraction rate of about twenty three percent for the fields that opened.
The biomass model improves spatiotemporal assessments of kelp forest size. This new method is accessible and fast enough to use operationally, which is why IMR can report field-level biomass estimates from Nordland with transparent uncertainty instead of only station level trends. Nevertheless, currently the biomass of dense but short canopies can be overestimated using the model, which is a limitation in measuring the recovery of kelp forests after harvest. Methods are being tested to help resolve this issue and improve model accuracy.
Laws And Practices To Implement The Scientific Evidence
To maintain a viable industry, it is critical that the scientific evidence and guidance is followed by law and policy makers. Previous assessments conducted further south in Vikna, have also followed a similar combination of monitoring, modelling and field rotation for adaptive management. The Nordland monitoring is crucial to expand this evidence base to determine whether the industry is acting sustainably and continued long-term monitoring is needed to observe how fields react to repeated harvesting.
Currently, kelp harvesting is prohibited at depths over 20 m to protect deeper and less dense stands along the coast. The regional regulations for southern Nordland also mean harvesting is limited to summer only windows, and harvesting is prohibited in protected UNESCO World Heritage areas without special permission. However, limited protections are in places for Norwegian kelp forests, which are one of its largest and most important marine habitats.
Importance For The PROTEUS Project And Northern Europe
The Institute of Marine Research that has driven the Nordland monitoring programme is a key scientific partner on the PROTEUS project. This Nordland programme is straightforward and cost-effective to replicate as diver-free video surveys and acoustic methods are widely available and can be standardised across sites. Spatial modelling allows field-level biomass and extraction maps to be created from in-situ data to scale up estimates of kelp forest biomass and health. These tools create a monitoring and assessment system that could also be used to guide restoration efforts in areas where kelp forests have been lost.
IMR as a long-term monitoring organisation, also provides clear guidance to policy makers bridging science and industry. That institutional continuity is a national asset and a resource for European collaborations that want to raise monitoring standards across regions.
For the PROTEUS project to deliver on its sustainability aims, it must consider the importance of these findings for kelp forest recovery times and continue to support biodiversity monitoring efforts.
The Bottom Line: Kelp Forests Can Recover After Harvesting, If Given Enough Time For Full Ecosystem Regeneration
The results from the Nordland monitoring provide indication that commercially harvested Laminaria hyperborea forests in northern Norway can recover their biomass within approximately five years, but the full ecological complexity and biodiversity value of the kelp forest takes closer to eight years to return. By combining underwater video, biological sampling, and acoustic surveys, IMR has developed one of the most operationally practical and scientifically robust kelp monitoring systems currently available in Europe, including improved estimates of standing stock and extraction rates. The findings support adaptive harvest rotations and show that present harvesting levels in southern Nordland have not prevented regrowth, although continued long-term monitoring is essential to assess repeated harvesting effects, species shifts, and grazing risks from sea urchins.
For Norway and the wider PROTEUS project partnership, the study demonstrates that sustainable kelp harvesting depends not only on restoring biomass, but also on allowing enough time for biodiversity and ecosystem functioning to recover.
Original author of reports: Henning Steen, Marine biologist researcher at the Institute of Marine Research, Norway
Translation and editing: Steinbeis Europa Zentrum and Sophie Corrigan, researcher at the Institute of Marine Research, Norway
Picture copyright: Institute of Marine Research, Norway
About the Circular Bio-Based Europe Joint Undertaking
The project is supported by the Circular Bio-based Europe Joint Undertaking and its members. The CBE JU is a €2 billion partnership between the European Union and the Bio-based Industries Consortium, funding projects to advance circular bio-based industries in Europe.
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Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the CBE JU. Neither the European Union nor the CBE JU can be held responsible for them.