Kelp industrial production: Potential impacts on coastal ecosystems (KELPPRO)

Background: Norway has a long coastline with clean and nutrient rich seawater, which provides ideal conditions for the cultivation of kelp. To ensure a long-term and profitable industry, kelp cultivation must be developed in a sustainable way with an understanding of possible impacts on the marine environment. The research project KELPPRO (2017-2020) investigated how cultivation of kelp impact the environmental condition and marine life and estimated the extent to which large-scale kelp cultivation will affect natural ecosystems positively or negatively. Field- and laboratory experiments, and numerical modeling were used to quantify the effect of kelp cultivation on the seafloor and in the open water masses, as well as to assess whether kelp farms play a role in spreading alien or endangered species. Numerical modelling showed that there is a great potential for cultivating kelp along the Norwegian coast, with a harvesting potential of 70 to 200 tonnes per hectare. Cultivation conditions along large parts of the Norwegian coast are good but also variable. Areas with stable and good nutrient supply, often at a good distance to the coast, stand out as particularly suitable and productive. Effects on seafloor habitats: Field measurement have shown that under normal operational conditions, 8 to 13% of harvested biomass is released to the environment per year. If the harvest is delayed until late summer, the loss can be >50% of the harvested amount. The released kelp is transported with the water currents, and a case study showed that >90% of the biomass ended up at the seafloor within 4 km of the kelp farm (at 0 to 100 m depth). The effects on the seafloor of released kelp were minimal, and no effects on biodiversity or ecological function were documented during normal operations. In contrast, field experiments with deposition of a large amount of kelp (>8 kg fresh kelp per square meter), corresponding to worst-case scenarios, showed a significant worsening of bottom oxygen conditions, reduction in animal diversity, and increased production of toxic sulphide. Degradation of deposited kelp was fast, and about 50% of the biomass had disappeared after 3 weeks, and more than 90% after 3 months, indicating reversible impacts on seafloor ecosystems. Laboratory studies showed that the decomposition time was longer for winged kelp (Alaria esculenta) than for sugar kelp (Saccharina latissima) and was depending on temperature and oxygen availability. The experiments demonstrated a high capacity for kelp turnover on the seafloor. However, the amount of kelp that constitutes the 'tipping point' from a bioresource for the foodweb to an ecosystem threat was not possible to quantify in this project. Effects on open water habitats: Effects of kelp cultivation on life in the water column are closely linked to the competition for nutrients. Field measurements showed that nutrient concentrations in the water around kelp farms, as well as the nutrient status of the phytoplankton, were unaffected by the cultivated kelp. Calculations showed that this applies regardless of the size of the kelp farm, as naturally occurring microalgae have a more efficient uptake of nutrients than kelp. A short-term reduction in the access to light in kelp farms (as when phytoplankton is drifting through) will not influence phytoplankton growth. The potential for water purification, i.e. reducing the negative effects of eutrophication through nutrient uptake, is related to when and how much nutrient kelp absorbs during growth and must be calculated specifically for relevant locations. Biodiversity and alien species: Kelp farms proved to function as artificial habitats, with similarities to natural kelp forests, only with fewer species and individuals. Results indicate that the location of the farm plays a role in the kind of communities that will settle in the farms and how farms will contribute to the spread of species. A mass occurrence of the alien species Japanese skeleton shrimp (Caprella mutica) was registered after harvest in 2019, indicating that empty farms may provide a substrate and accelerate the spread of alien species. The fact that different population genetic groupings of sugar kelp are found in different ecoregions gave basis for maintaining the advice not to move kelp plants between ecoregions. Dissemination: The KELPPRO output includes peer-reviewed papers (6 published, 4 submitted, and >8 in preparation), ISBN-reports (5), Master theses (4), popular science contribution (24) and a wealth of talks and posters (52) on the subject. Included are guidelines towards a management strategy for future monitoring of kelp cultivation, targeting Norwegian management agencies. When upscaling the kelp industry, effects on the seafloor, the spread of species and spread of genetic material is recommended to be included in future research to ensure the growth of a sustainable industry.

KELPPRO has produced novel insight and its scientific results are published in peer review journals, as ISBN reports, as popular science reports, and MSc theses. All of which have contributed to build a scientific competence on ecological impacts of kelp farming in Norway and internationally. The project has established a baseline for the assessment of positive and negative ecosystem impacts of kelp cultivation, and the results have received profound attention and is already applied by other scientific projects and by the kelp cultivation industry. KELPPRO results are expected to form a basis for environmental guidelines and improve the current policy and management practice towards a long-term resilience and sustainable kelp cultivation industry. In addition, KELPPRO has contributed empirical data and knowledge to new research proposals and for formulation of a scientific fundament for kelp cultivation as a climate mitigation solution through atmosphere carbon dioxide removal.

Norway has the potential for being world leading in the fast expanding industry with production of lower-trophic-level marine species, i.e. for instance the large seaweeds (kelp). This is an attractive industry supplying the global marked with resources for food, medicine, bio-fuel and cosmetics. To lead this emerging industry in a sustainable manner, Norway needs knowledge on how large-scale industrial kelp production will impact marine areas in both positive and negative ways. Positive impacts are kelp uptake of nutrients and CO2, reducing marine eutrophication and CO2 concentration (i.e. reducing ocean acidification). Negative impacts are depletion of limited nutrients or the depositing of large quantities of detached kelp on the seafloor, leading to poor environmental conditions, oxygen deficiency, and change in natural biodiversity. KELPPRO will provide an integrated assessment of the positive and negative impacts of large-scale industrial kelp production on the Norwegian coastal environment. It will deliver basic knowledge and predictions on future ecological consequences, and provide guidance for decision makers, managing agencies, and end users. KELPPRO is a multidisciplinary project integrating kelp ecology, biodiversity, seafloor biogeochemistry, water columns physics and chemistry, spatial modelling and mathematical projections. The project will carry out mesocosms experiments, field investigations, and numerical modelling by bringing together national and international experts on relevant fields, in close collaboration with the emerging kelp cultivation industry in Norway. KELPPRO results will provide robust scientific knowledge to support decision making and management of coastal environments prone to large-scale industrial production of kelp.