Blue forest cultivation

What

The term “blue forest” is used to describe coastal or oceanic ecosystems formed by macro algae or marine plants. Examples include kelp forests, rockweed and salt marshes. Blue forests play an important role in marine ecosystems, as they provide food and refuge to many marine species. In addition, they often improve water quality, protect shorelines from erosion, and can capture and store large quantities of atmospheric CO2. Artificial blue forests refer to the cultivation of marine vegetation, or the introduction of vegetation on artificial reefs in coastal or oceanic ecosystems. 

 

Coastal graphic: Before

Coastal ecosystem before NbS have been implemented

Coastal graphic: After

Coastal ecosystem after NbS have been implemented

 

Where

In coastal areas, cultivation of blue forests can be used to mimic some of the ecological functions of a natural kelp forests and other macroalgae in areas where the blue forests have been reduced or lost, but temporarily before the biomass is harvested. Artificial reefs can also be used to create a suitable structure for blue forests on a more permanent basis, to enhance marine biodiversity.  

However, there is also great potential for blue forest cultivation in the open ocean, where macroalgae do not naturally occur. In this case, the primary purpose of artificial blue forests can be to increase the uptake and storage of atmospheric greenhouse gases, or to use the biomass for other purposes (food, biogas, environmentally friendly plastic, etc.).  

Why

Cultivating blue forests can have many societal and ecological benefits. The four main benefits are:  

  1. Biodiversity enhancement: As blue forests provide food and shelter to many species, introduction of blue forests may enhance biodiversity. Artificial reefs may provide shelter to key predators in the ecosystem, as e.g. predators on sea urchins, helping to regain ecological balance in disturbed ecosystems.

  1. Climate change mitigation by capturing and storing of greenhouse gases. Only a small portion of the world’s oceans can be described as blue forests (less than 0.5%). Yet it is estimated that natural blue forests account for 70% of carbon storage in the ocean. Therefore, the potential of artificial blue forests to capture and store carbon is extremely large, especially when placed in the open ocean.  

  1. Water management through regulation of water quality. Blue forests reduce the turbidity of the water by absorbing nutrients. This improves the potential for photosynthesis, which in turns increases the level of oxygen in the water. Therefore, blue forests regulate and help improve water quality. 

  1. Climate change adaptation by prevention of coastal erosion. Finally, artificial blue forests can be used to reduce coastal erosion and protects coasts from storm surges, by absorbing wave energy.   

How

Cultivation of blue forests can take many forms. Requirements and methods for implementation highly depend on the location, the type of species, the ecological status of the local ecosystem, the purpose of the cultivation, local disturbances etc. It is important to use local species to avoid affecting the genes of the native species. Seeds or cuttings can be sown on ropes or other substrates, or artificial reefs can be seeded naturally from local macroalgae.  

Offshore seaweed farming can also be developed in various ways, depending on the overarching goal, species, scale etc. For example, macroalgae require a square-shaped floating structure, to hold cultivation lines or nets in place. Seaweed is attached to these lines, which are submersed a few meters below the surface. In the case of North Sea Farm 1, cultivation lines are placed within, and attached to an offshore wind-farm.         

Potential outcomes 

The use of artificial blue forests yields different outcomes when applied to coastal areas compared to offshore. 
 
Cultivation of macroalgae and the use of artificial blue forests in coastal waters: 

  • Macroalgae are native species here and will provide shelter and food to many marine species, which in turn may attract marine predators. Thus, the cultivation of blue forests may enhance biodiversity temporarily before the biomass is harvested.  

  • Introduction and growth of blue forests on artificial reefs will improve water quality and produce oxygen. The reefs may protect coasts from erosion. 

  • The harvested biomass can be used to provide food, fertilizer and medicine products.  

Offshore cultivation of blue forests differs from coastal cultivation as it introduces a new species - and a high concentration of a monoculture of a species, as well as an artificial structure to the environment.  

  • One important purpose of offshore cultivation is sequestering of CO2. CO2 is captured by the plants and have the potential to be transported to the bottom of the ocean, where it can be buried and removed from exchange with the atmosphere. However, the effectiveness and extent of this use of kelp biomass is uncertain. 

  • There is also a high potential for using cultivated blue forest biomass as raw material for other products as food, biogas, environmentally friendly plastic, etc.  

ATTENTION  

Artificial reefs may promote the spread of invasive species. It is also important to use local strains of the species when seeding the ropes or the artificial structures.  

Offshore blue forest cultivation is likely to affect the local ecosystems in several ways, but it is difficult to evaluate whether these impacts can be considered positive or negative. This is a common problem with the introduction of artificial structures into ecosystems. For example: 

  • The artificial blue forest can attract large numbers of fish, seabirds and other organisms, which may seem positive at first. However, as these aggregations did not occur naturally in the local environment prior to the cultivation project, it is difficult to predict the long-term implications of these modifications for the natural local ecosystem.  

  • Artificially induced algae-blooms may be harmful to local ecosystems, as they can affect the chemical and physical properties of seawater. 

How much do we know?

A lot is known about the role of natural blue forests on ecosystem functioning and its positive effect on biodiversity. The potential of blue forests to capture and store greenhouse gases has become a topic of much interest in recent years. However, blue forest cultivation and introduction of artificial blue forests into the sea is relatively new, and potential ecological consequences are still mostly unknown.  

In Northern Norway, there is a need to restore 5000 km2 of grazed kelp forest. These areas have suitable substrate for kelp forest and there is no need to introduce artificial blue forests here. All experience indicates that the kelp plants will return by themselves if the sea urchins are removed.  

The use of “green gravel” and seeding or transplanting kelp plants is only relevant if small-scale trials show recruitment failure of the native kelp species. In southern Norway, the loss of e.g. sugar kelp is linked to multiple pressures, such as ocean warming, eutrophication, sedimentation, and ocean darkening. Here it is probably unlikely to restore the natural kelp forests by using artificial reefs until the drivers of the kelp loss have been mitigated. However, in all areas, artificial blue forests have the potential to enhance marine biodiversity locally, on small-spatial scale.  

Costs 

Costs are highly dependent on site-specific conditions, goals and scale. Kelp farming is a new self-sustaining industry. The use of artificial blue forests in restoration projects are also new and not well tested and applied.  Hence, we have little knowledge of their costs. Furthermore, there is a large need to develop marine life-friendly materials in kelp farms as well as in the artificial structures, hence R&D costs should be included in pilot studies. 

Location: coast of Trøndelag, central Norway 

Which ecosystem type: Coastal 

Title/ name of the NbS: JIP Seaweed Carbon Solutions 

Summary: A small scale offshore seaweed farm of the coast of Trondelag. 

Relevant links: New seaweed farm off the Norwegian coast seeks to remove CO₂ from the atmosphere 

Location: Within the offshore wind farm ‘Hollandse Kust Zuid’ (HKZ), ca. 18 kilometres off the coast of Scheveningen 

Which ecosystem type: Offshore/ marine 

Title/ name of the NbS: North Sea farm 1 

Summary: A pilot project to cultivate seaweed within an offshore wind farm 

Relevant links: NSF1 - North Sea Farmers 

Location: The method was developed in Norway and is currently tested by 20+ research groups on four continents. 

Which ecosystem type: Coastal 

Title/ name of the NbS: Green gravel 

Summary: Small rocks are seeded with kelp and reared in laboratory until 2–3 cm long, before out-planting to the field. The out-planted kelp had high survival and growth in a 9-month survey, even when dropped from the surface. The technique is cheap, simple, and does not require scuba diving or highly trained field workers. The method can be used to introduce genes from more resilient kelp populations onto vulnerable reefs if needed. So far, the method has had low success over a longer period of time.  

Relevant links: Green gravel: a novel restoration tool to combat kelp forest decline. For restoration of kelp in sea urchin barrens, see Christie et al. 2024. Based on current knowledge, seeding is not necessary as kelp comes back by themselves when sea urchin density is sufficiently reduced. 

Christie H, Moy F, Fagerli CW, Rinde E, Mette S, Tveiten L, Strand HK (2024) Successful large-scale and long-term kelp forest restoration by culling sea urchins with quicklime; and supported by crab predation. Marine Biology. 

Duarte, C. M., Wu, J., Xiao, X., Bruhn, A., & Krause-Jensen, D. (2017). Can seaweed farming play a role in climate change mitigation and adaptation?. Frontiers in Marine Science, 4, 100. https://doi.org/10.3389/fmars.2017.00100 

Eger, A. M., Marzinelli, E. M., Christie, H., Fagerli, C. W., Fujita, D., Gonzalez, A. P., ... & Vergés, A. (2022). Global kelp forest restoration: past lessons, present status, and future directions. Biological Reviews, 97(4), 1449-1475. https://doi.org/10.1111/brv.12850 

Fredriksen S, Filbee-Dexter K, Norderhaug KM, Steen H, Bodvin T, Coleman MA, Moy F, Wernberg T (2020) Green gravel: a novel restoration tool to combat kelp forest decline. Scientific Reports 10:3983  

Frigstad, H., Gundersen, H., Andersen, G.S., Borgersen, G., Kvile, K.Ø., Krause-Jensen, D., Boström, C. et al. (2021) Blue Carbon–climate adaptation, CO2 uptake and sequestration of carbon in Nordic blue forests: Results from the Nordic Blue Carbon Project. Nordic Council of Ministers. 

GRID-Arendal, Institute for Marine Research, Norwegian Institute for Water Research, 2022. Norwegian Blue Forest Network Annual Report 2021.  

Krause-Jensen, D., Gundersen, H., Björk, M., Gullström, M., Dahl, M., Asplund, M. E., ... & Hancke, K. (2022). Nordic blue carbon ecosystems: Status and outlook. Frontiers in Marine Science, 9, 847544. https://doi.org/10.3389/fmars.2022.847544 

Ocean Visions and Monterey Bay Aquarium Research Institute (2022). Answering Critical Questions About Sinking Macroalgae for Carbon Dioxide Removal: A Research Framework to Investigate Sequestration Efficacy and Environmental Impacts. Available online at: New Funding Tool Available for Seaweed Researchers 

Verbeek, J., Louro, I., Christie, H., Carlsson, P. M., Matsson, S., Renaud, P. E. (2021). Restoring Norway’s underwater forests. A strategy to recover kelp ecosystems from urchin barrens. SeaForester, NIVA & Akvaplan-niva, Report, 2021 

WHOI – Fueling the future (4 Oktober 2017) Fueling the Future – Woods Hole Oceanographic Institution (whoi.edu) 

Seaweed Solutions industrial-scale offshore seaweed cultivation (businessnorway.com) 

Ocean-Visions-Sinking-Seaweed-Report_FINAL.pdf (oceanvisions.org)