OPEN OCEAN CULTIVATION OF SEAWEED – SCALING UP PROVEN CONCEPTS

Introduction

We are facing a global crisis. Climate change and loss of biodiversity are a fact (Dasgupta, 2021). At the same time, the global human population is increasing, hence, sustainable, healthy, and tasty food is needed (WFS Webinar, 2021). Sustainably cultivated seaweeds in the open ocean are being mentioned as a blue biomass resource that could amend the negative impact of climate change and loss of biodiversity and add new healthy food and feed products to the market (Lange et al., 2021).

The large brown seaweeds (kelp) are among the fastest-growing crops on the planet. To grow, they only need sunlight, CO2, and nutrients that are naturally available in the ocean. When this productivity becomes commercially exploited and transferred to the large surface of the open ocean, in sites with sufficient nutrients, large quantities of biomass can be produced. The CO2 and nutrient mitigation provided by the kelp production improve ocean health and add new kelp-forest-habitats that provide a shelter, feeding chamber, and nursery for various low and high trophic animals.  

The open ocean environment has previously been a major challenge for seaweed production due to the high wave exposure and deep waters (Bak et al. 2020). Nevertheless, the SME Ocean Rainforest has developed a MacroAlgal Cultivation Rig (MACR) that is suitable for these harsh ocean environments (Bak et al. 2018). The challenge is immediately to take this proven concept and bring it to a level of 1 Mio tons wet weight of annual production with a high economic, social, and environmental impact in 2030.

This work is part of the ongoing EU H2020-project AquaVitae www.aquavitaeproject.eu and the project SELBREED which is a project collaboration between Ocean Rainforest and Hortimare.

Methods

The main challenge is to reduce operational expenditures (OPEX) and capital expenditures (CAPEX) of production to make the business profitable. The methods investigated to reduce cost are:

• Upscaling operation through further rig development
• Testing re-use of aquaculture equipment
• Developing mechanized seeding, harvesting, and landing technics
• Increase yield through selective breeding
• Make use of multiple partial harvesting and optimize this method 

Results

Upscaled macroalgal cultivation in the Faroe Islands was tested by improving the MACR further allowing the rig to hold a production of 40 km seeded grow line in an 8-ha area which has now been tested during winter storms and proven the survivability of the second MACR-version with a total of 100 km grow lines deployed and a productivity of 30 tonnes ww/ha/year.

Discarded anchors and buoys were re-used in the deployment of two new rigs, and the implementation of second-hand equipment was analyzed and found to reduce the CAPEX by 41% and lowered the CO2-footprint by 46% in an optimal situation. However, the more the seaweed industry will scale up, the more limited the re-use opportunities will be.

Besides upscaling, the project has identified new harvesting methods that enable maximum yield and reduced OPEX. Yet there is a need to reduce OPEX even further and additional technological development to upscale the operation is needed.

The upscaling in seeding material for the 80 km of new grow lines was made without further investments in hatchery equipment, thus keeping a low cost of production. The seeding of ropes still needs to be automated and yield quantities should be improved by selective breeding. This is a challenging part of future upscaling.

The yield is the main income driver. Today a vertical line of 10-meters yields 25 kg ww per harvest, being harvested twice a year, it yields 50 kg ww/grow line which occupies a sea surface area of one square meter. The aim is to make a crossbreed that can produce 30% more within the coming 2-3 years. 

The company has discovered that sugar kelp (Saccharina latissima) can regrow after being harvested. The use of multiple partial harvesting of S. latissima (up to 6 harvests without re-seeding) has allowed making the highest known harvesting yield per seeded meter growth line and has reduced the production cost by 75% (Bak et al. 2018). A better understanding of the growth pattern and effect of partial harvesting will enable maximum yield and reduced OPEX.

The next step in the AquaVitae project will be to establish criteria for site selection and find suitable sites for large-scale production (>500 ha) in open-ocean environments in the Atlantic Ocean. Thus, the Faroese seaweed production adds crucial results for the future expansion of this underexploited aquaculture industry.

References

Dasgupta, P. (2021), The Economics of Biodiversity: The Dasgupta Review. London: HM Treasury.

World Food Summit Side-Event (2021), Short-cut to a healthy & sustainable diet and reduced use of antibiotics by microbial solutions and upcycling of food processing side-streams. Webinar.

Lange, L. et al. (2021), the 3F Marikat folder on Blue BioEconomy: Den blå bioøkonomi – værdiskabelse fra den blå biomasse.