The use of cultivated seaweeds as a feedstock for multiple industrial applications has gained increasing interest in the Western World over the past decades. Norway has an extensive coastline and a well-established aquaculture sector offering suitable preconditions for developing large-scale cultivation of seaweed biomass both in monoculture and in Integrated Multi-Trophic Aquaculture (IMTA) systems. Recent efforts from research, industry and public authorities have been committed to develop a Norwegian bio-economy based on cultivated seaweed, focusing on cultivation and processing of the biomass. This review reports on the status of seaweed aquaculture in Norway, supported by production data collected since the delivery of the first commercial cultivation permits at sea in 2014. Although novel product developments are currently limited, future industrial perspectives based on cultivated biomass are being discussed. Upscaling from experimental cultivation schemes to commercial production requires a thorough assessment of the risks and benefits associated with seaweed aquaculture, as well as the development of a regulative framework adapted to this industry. Issues associated with upscaling the macroalgal production that needs to be addressed includes (i) genetic interactions between cultivated and wild crops, (ii) impacts of seaweed cultivation on surrounding ecosystems, (iii) epiphytes and diseases, (iv) area utilization and (v) threats from climate change. Addressing these issues and adapting production practices will ensure the environmental and economic sustainability of an emerging industry based on cultivated seaweed biomass in Norway.

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Seaweed aquaculture in Norway: recent industrial developments and future perspectives

Biofouling in marine aquaculture is one of the main barriers to efficient and sustainable production. Owing to the growth of aquaculture globally, it is pertinent to update previous reviews to inform management and guide future research. Here, the authors highlight recent research and developments on the impacts, prevention and control of biofouling in shellfish, finfish and seaweed aquaculture, and the significant gaps that still exist in aquaculturalists’ capacity to manage it. Antifouling methods are being explored and developed; these are centred on harnessing naturally occurring antifouling properties, culturing fouling-resistant genotypes, and improving farming strategies by adopting more sensitive and informative monitoring and modelling capabilities together with novel cleaning equipment. While no simple, quick-fix solutions to biofouling management in existing aquaculture industry situations have been developed, the expectation is that effective methods are likely to evolve as aquaculture develops into emerging culture scenarios, which will undoubtedly influence the path for future solutions.

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Biofouling in marine aquaculture: a review of recent research and developments

Sugar kelp (Saccharina latissima) is an abundantly available macroalgae species along the Norwegian coast, and there is currently emerging an industry based on seaweed cultivation. In this study, the biomass growth of cultivated S. latissima deployed in February was studied at cultivation depths of 3 and 8 meters (m) and monitored over the period of May, June, and August. The highest biomass production was observed in June at the depth of 3 m (38.3 kg wet weight m−2). Furthermore, all seaweed samples underwent a detailed chemical characterization including analysis of carbohydrates (glucose, mannitol, fucose, xylose, uronic acids), amino acids and minerals. The macroalgae deployed in February at 3 m depth and sampled in June had the highest proportion of total sugars (534.5 g kg−1 of DM) and the lowest content of ash (252.7 g kg−1 of DM). Thus, cultivation at 3 m and harvesting in June are suitable when the feedstock is used for biochemical production of fuels and chemicals. Macroalgae deployed at 8 m depth and harvested in August had the highest proportion of total amino acids (242.4 g kg−1 DM) and ash content (411.5 g kg−1 DM). This biomass may be suitable as a nitrogen and mineral source in microbial growth media. Overall, the choice of cultivation depth and harvesting time depends on the intended use of the seaweed biomass.

Seasonal and depth variations in the chemical composition of cultivated Saccharina latissima

We have evaluated the cultivation potential of sugar kelp (Saccharina latissima) as a function of latitude and position (near- and offshore) along the Norwegian coast using a coupled 3D hydrodynamic-biogeochemical-kelp model system (SINMOD) run for four growth seasons (2012-2016). The results are spatially explicit and may be used to compare the suitability of different regions for kelp cultivation, both inshore and offshore. The simulation results were compared with growth data from kelp cultivation experiments and in situ observations on coverage of naturally growing kelp. The model demonstrated a higher production potential offshore than in inshore regions, which is mainly due to the limitations in nutrient availability caused by the stratification found along the coast. However, suitable locationsareas for kelp cultivation were also identified in areas with high vertical mixing close to the shore. The results indicate a latitudinal effect on the timing of the optimal period of growth, with the prime growth period being up to 2 months earlier in the south (58 °N) than in the north (71 °N). Although the maximum cultivation potential was similar in the six marine ecoregions in Norway (150-200 tons per unit area per year) in the six marine ecoregions in Norway, the deployment time of the cultures seems to matter significantly in the south, but less so in the north. The relevance of the results is discussed with a view towards use in decision support tools and a management context. The results are discussed, focusing on their potential significance for optimized cultivation and to support decision making towards sustainable management.

The Kelp Cultivation Potential in Coastal and Offshore Regions of Norway

Overview of 3 year precommercial seafarming of Macrocystis pyrifera along the Chilean coast

Integrated multi-trophic aquaculture (IMTA) has the potential of reducing open-cage fish farming impacts on the environment while also introducing new value chains. The aim of this study was to investigate the growth and composition of the kelp Saccharina latissima in salmon-driven IMTA, and to assess the spatial extent of the influence of salmon derived nitrogen in order to evaluate the upscaling potential for IMTA. S. latissima was cultivated 100, 200 and 1,000 m east and 1,000 m west of a 5,000 tonnes salmon farm in Western Norway from February to September 2013. The proportion of salmon derived nitrogen available for the kelp showed a clear decline with distance from the farm. Accordingly, the kelp cultivated near the salmon cages grew faster during the spring season, and growth rate decreased with increasing distance from the farm. A spatially explicit numerical model system (SINMOD), including compartments for dissolved nutrients and kelp growth, was tuned to the field data and used to investigate the potential for upscaling IMTA production. The model was used to introduce a new metric – the impacted area IA - for the areal effects of IMTA in terms of the increase in production by IMTA. The model showed that a 25 hectare kelp farm in the vicinity of the studied salmon farm could take up 1.6 of the 13.5 tonnes of dissolved inorganic nitrogen released during kelp cultivation, amounting to almost 12 % of the ammonia released during the cultivation period from February to June. The 25 hectare kelp farm would have a production yield of 1,125 tonnes fresh weight (FW), being 60 % more than that of a non-IMTA kelp farm, while a 20 % increase of kelp FW could be obtained over a 110 hectar area in salmon-driven IMTA. To achieve an even mass balance, an area of approximately 220 ha-1 would be needed to cultivate enough kelp to fix an equivalent of the nitrogen released by the fish.

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The Potential for Upscaling Kelp(Saccharina latissima) Cultivation in Salmon-Driven Integrated Multi-Trophic Aquaculture (IMTA)

Biofouling on cultivated kelp in open sea conditions is a challenge when fouling species such as the encrusting bryozoans Membranipora membranacea and Electra pilosa develop colonies that cover the surface of the kelp lamina. The bryozoan colonies make the flexible lamina brittle and susceptible to breakage and reduce the commercial value of the biomass for both human consumption and industrial applications. The development of the bryozoan fouling on cultivated Saccharina latissima in temperate coastal waters was studied at two locations in Norway from April to September. The time of settling and development of colonies of M. membranacea and E. pilosa were characterized. Sampling of bryozoan larvae abundance at the cultivation locations showed that the bryozoan colonies settled on the cultivated kelp in mid-June at both locations, followed by a rapid colony growth during late June and July. In August and September, the kelp was highly degraded by the bryozoan coverage and highly subjected to breakage of the lamina. Membranipora membranacea was the most prevailing of the two species. Although abundant at all cultivation depths, the results showed a decrease in bryozoan coverage with increasing depth. From a commercial point of view, S. latissima deployed in temperate Norwegian coastal waters in winter should be harvested in early June to avoid the negative impact from bryozoan fouling.

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Julia Fossberg

Papers

The Potential for Upscaling Kelp(Saccharina latissima) Cultivation in Salmon-Driven Integrated Multi-Trophic Aquaculture (IMTA)

Development of bryozoan fouling on cultivated kelp ( Saccharina latissima ) in Norway