Seaweed cultivation in the Faroe Islands: An investigation of the biochemical composition of selected macroalgal species, optimised seeding technics, and open-ocean cultivation methods from a commercial perspective

A global need for sustainable produced biomass has kick-started the development of commercial macroalgal cultivation in Europe. In contrast to the well-established nearshore cultivation in Asia, a Faroese company, Ocean Rainforest, has developed a MacroAlgal Cultivation Rig (MACR) that is suitable for oceanic conditions (>50 m water depth).

The design has proven itself scalable since 10 MACR’s have been in operation since 2010. Still, the challenge is to reduce the cost of production to be competitive within the global market. The purpose of this PhD project was to optimize the cultivation method at sea for an applicable and economically profitable industry.

The kelps Saccharina latissima and Alaria esculenta were cultivated on a commercial scale with 40 km of growth lines deployed in the Faroe Islands. The aquaculture output (AO; yield/ha/year) was optimised and multiple partial harvesting method was tested. Growth and yield were monitored through a three-year period at two cultivation sites, and the biochemical composition was determined from S. latissima, A. esculenta and Laminaria digitata samples collected monthly (2015-2016).

Also, the purpose was to obtain indepth knowledge about the target biochemical composition of cultivated brown macroalgal species to plan harvest, decide on product applications, and plan for future biorefinery processes. Analyses of dry matter, minerals (ash), protein, carbohydrate, lipid, amino acid profile, fatty acid profile, antioxidant activity, α-carotene, β-carotene and D-vitamin, iodine, lead, mercury, cadmium and arsenic including inorganic arsenic were performed, and evaluated in relation to their interannual, seasonal, site and depth variations.

Finally, the purpose was to obtain new optimised seeding techniques of two kelp species and to find a way to the more challenging seeding and obtaining biomass of the red macroalga Palmaria palmata. Saccharina latissima sporophytes were seeded directly on ribbons using a binder and the method showed same length and density as when using the more traditional “twine around rope” method.

Also, the cost was reduced by 13% or 23% by using this direct seeding method on ribbons or nylon ropes, respectively. Palmaria palmata was successfully direct seeded for the first time, though having a low density. A very high density was obtained by using natural seeding over winter from nets placed on wild populations.

The results of the biochemical composition showed a significant variation of several compounds between species and seasons, but not between years, cultivation depths and sites. There was a seasonal trend that dry matter and carbohydrates concentrations went up in winter where ash and protein were lowest, and the opposite during summer.

Saccharina latissima had high carbohydrate (42-57% of dw) and ash concentration (36-42% of dw), lower content of protein (11-14% of dw), and small amounts of lipids (2.4% of dw). Vitamin D and α-carotene were not detected in any of the species and a low antioxidant activity was revealed. β-Carotene was found at 10-22 ppm of dw.

Iodine concentration was high for S. latissima and L. digitata (3998-5361 ppm of dw) and lower for A. esculenta (234 ppm of dw) with lowest concentration during harvest season. The levels of heavy metals found within this work were in similar range as other food sources and below threshold values. The results can be used directly as product documentation and the results revealed that depth and site variation were not significant for the biochemical composition.

The results made a great contribution to the better understanding of the biochemical composition of the cultivated macroalgae and that important variables are species and season. For the first time, multiple partial harvesting was proven successful for S. latissima and A. esculenta with up to five harvests of the same biomass without reseeding.

Saccharina latissima was suitable for two harvests per year and A. esculenta could be harvested once a year. In the second-year of cultivation fouling of other macroalgal species occurred on the lines and selfseeded L. digitata could also be harvested. The multiple partial harvesting alone reduced the operational cost of the MACR from € 36.73 to less than € 9.27 per kg dry weight (dw) of cultivated S. latissima.

The 10 m vertical growth lines seeded with S. latissima had a mean yield of 0.29 kg dw per meter per harvest when four partial harvests were made over a two-year period. The AO was found to be 1.4-4 tonnes dw per hectare per year (including handling space). The mean yield and AO are one of the first of its kind under open-ocean cultivation with commercial-scale testing and without extrapolating data from research trials.

This work has thus optimised commercial kelp cultivation methods in the Faroe Islands.