Optimizing Seaweed Biomass Production - A Two Kelp Solution

Optimizing Seaweed Biomass Production - A Two Kelp Solution | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Optimizing Seaweed Biomass Production - A Two Kelp Solution Michael Stekoll, Alf Pryor, Meyer Alexandra, Scott Lindell, David Bailey, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4263270/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Interest in farming kelps has grown beyond using kelp for food, feed or biofuels. There is considerable interest in generating biomass from seaweed for use in bioplastics and other products that would substitute for petroleum-derived products. For these uses to be viable, large amounts of biomass are needed. Very large kelp farms can be expensive to build and maintain, leading to the need to optimize the biomass per unit area. Although close spacing of growlines can lead to poor growth, a viable approach may be to grow two species of kelps together: one that hangs down and one that is buoyant, growing up. This system would increase the spacing in three dimensions. In Alaska, Saccharina latissima is commonly grown hanging down from longlines. One of the buoyant Alaskan kelps is Nereocystis luetkeana. Because there are commercial uses for wild-harvested Nereocystis in Alaska, we undertook a preliminary trial in Kodiak, Alaska that grew both Saccharina and Nereocystis in the same longline array. Closely spaced lines were seeded the first week of February 2023 and set at 3m below the surface. The arrays were harvested in late June 2023. Total yields were greatest on the combined arrays, followed by the Nereocystis only and Saccharina only arrays. Despite having 45% fewer grow-lines, the total yield of the Nereocystis on the combined arrays was statistically similar to the Nereocystis only arrays. These results may have significance for large scale macroalgal production. Macroalgae aquaculture bull kelp sugar kelp Nereocystis Saccharina Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction The mariculture of seaweed in Alaska, like much of the US, is less than a decade old (Kim et al. 2019 ). A kelp farming demonstration project was initiated in 2019 funded by the US Department of Energy’s MARINER Program whose focus was maximizing yield per lease area by examining how practically and closely cultivation lines can be spaced on an interconnected array to grow Saccharina latissima (sugar kelp) (hereafter as Saccharina ). Results from three years of farm trials showed that spacing cultivation lines by as little as 0.76–0.85 m does not negatively affect the yield of Saccharina per meter of line. The yield varied each year between 6 and 9 kg m − 1 , which is similar to average yields of farmed Saccharina on independent lines as reported in the Northeastern US (Brayden and Coleman 2023 ) and Europe (Forbord et al. 2020 ). However, it is considerably lower than potential yields found in the farmed congeneric species, Asian kombu ( Saccharina japonica ), which, after more than 40 years of selective breeding, nears 30 kg m − 1 (Hwang et al. 2022 , Jung et al. 2024 ). One of the goals of the Department of Energy’s MARINER Program is to reduce the cost of production of seaweed to less than $ 100 per dry metric ton in order for it to be competitive with other land-based crops used as biofuel feedstocks. Our techno-economic analysis of kelp farming shows that yield per unit area is the major driving force for lowering the cost of production (Kite-Powell et al. 2022 ). A sugar kelp genetic selection and breeding program could eventually match the relative yield of Asian kombu by developing high-yield strains. Indeed, in the Northeast US a MARINER funded breeding program for sugar kelp has achieved marked improvements in yield (Li et al. 2022 ) with an average over 10 kg m − 1 , and a single cross yielding 28 kg m − 1 . However, current regulations in Alaska require that kelp seedlings come from random mating of meiospores from 50 wild individuals collected from within 50 km of the farm site. Because selective breeding is effectively outlawed in Alaska, we examined ways to markedly increase yield by more fully using the water column with the co-culture of negatively buoyant Saccharina and another floating kelp species. The premise for this co-culture project was that the floating kelps, growing near or on the same line, will not compete significantly with Saccharina. Each species will occupy its own vertical space so that there will not be competition for space, nutrients or light for the first few months of growth. The only issue might be competition for light when the kelps get larger in the last month of the growing season, and as they approach harvest size. We hypothesized that the overall yield of these co-culture systems will be significantly more than the yield of either crop grown alone. A further benefit is that the floatation provided by the floating kelps may offset the need to add buoyancy to the Saccharina longlines prevent sagging. In Alaska there are three species of floating kelps: Macrocystis integrifolia (giant kelp), Nereocystis luetkeana (bull kelp) (hereafter as Nereocystis ), and Eualaria fistulosa (dragon kelp). Currently, Nereocystis already has commercial value as a food source, but wild harvests cannot keep up with demand. Several organizations have grown Nereocystis with mixed success (Stephens et al. 2023 ). Recent work in California grew Nereocystis with wet weights greater than 16 kg m − 1 on a five-line array (K. Barbery, personal communication). Using information from that and other projects we designed a demonstration project to incorporate growing both Saccharina and Nereocystis side by side on 9-line arrays to determine if increased yields could result from using a two-crop system. To our knowledge, this is the first publication to report on floating and hanging kelps farmed in close proximity. Materials & Methods 2.1 Collecting parent material - Nereocystis and Saccharina seed for the project was produced in the Blue Evolution Hatchery housed at the Kodiak Fisheries Research Science Center in Kodiak, AK (permit 2017-104-HA-WE). Sorus tissue was collected from 50 wild Saccharina in late September 2022 from Trident Basin near Kodiak, AK, and Nereocystis in December 2022 from the coastline adjacent to the Alaska Ocean Farms Woody Island lease in Kodiak. Sori were collected via Alaska Department of Fish and Game protocol to create a meiospore solution with a concentration of 1,000 spores mL − 1 of sanitized seawater (Gruenthal et al. 2022). Seawater from Trident Basin was filtered via sand filtration, then sanitized by mechanical filtering down to 0.5 µ and then passed through an ultraviolet water sterilizer (Redmond et al. 2014 ). Sori were cleaned of surface contamination and other organisms by wiping with a clean paper towel. Sori were then soaked for one minute in a solution of 4% iodine and sanitized seawater, rinsed in sanitized seawater, and dried with paper towels (Augyte et al. 2017 ). Cleaned, dried sori were then placed in layers of dry paper towel and stored in sealed plastic bags at 4 ± 1°C and total darkness for 24 hours in a laboratory fridge (Flavin et al. 2013 ). 2.2 Hatchery procedure - After 24 hours the sori were removed from cold storage and placed in 1,000 mL beakers of sanitized seawater. The beakers were stored at 11 ± 1°C, exposed to 60 µmol m − 2 s − 1 irradiance, and checked for meiospore release every 30 minutes (Redmond et al. 2014 ). Meiospore release was verified by examining a 1 mL water sample from the release beakers via microscopy for motile meiospores. Meiospore density per mL seawater was counted using a hemocytometer. Stocking density was calculated using the following formula: VMS = DSC/(RWC/VSA), where VMS is the volume meiospore solution needed for stocking aquaria at 1,000 meiospores mL − 1 , DSC is the desired stocking concentration of meiospores (1,000 spores mL − 1 ), RWC is the release water concentration of meiospores (spores mL − 1 ), and VSA is the volume of seawater in the aquaria (Flavin et al. 2013 ). This process was repeated for three days until sufficient meiospore release was observed to produce 1,000 spores mL − 1 seawater in the hatchery aquaria. The calculated volume of release water was added to the hatchery aquaria containing the seed spools. Seed spools were composed of 7.62 cm diameter x 23 cm sections of PVC pipe with ~ 61 m of 1.5 mm nylon string (Holdfast® Tufting Twine, Ludlow® Series, A&E Industrial Textiles) wound round the exterior. Germanium dioxide (GeO 2 ) in a deionized water solution was added to the tanks to achieve a concentration of 0.002 mg L − 1 to deter diatom growth (Shea et al. 2007). F/2 seawater medium (parts A and B) (Guillard 1975 ) was added to the tanks to achieve a volume of 0.29 mL L − 1 to encourage spore settlement and gametophyte development (Ratcliff et al. 2017 ; Setthamongkol et al. 2015 ). The spools were left in total darkness at 11 ± 1°C for 24 hours (Kerrison et al. 2016 ). After 24 hours the spools were transferred to the main hatchery and illuminated with fluorescent lighting with an irradiance of 30 µmol m − 2 s − 1 for 12 h dark and 12 h light and a temp of 11 ± 1°C (Redmond et al. 2014 ). Irradiance was increased by 15 µmol m − 2 s − 1 per week for 2 weeks and then held at 60 µmol m − 2 s − 1 for the duration of hatchery cultivation (Augyte et al. 2017 ). The seawater in the aquaria was drained and replenished 2x per week during the hatchery period. During water changes both GeO 2 and F/2 were replenished in the aquaria at the same concentrations as during stocking to deter diatom recruitment and promote sporophyte growth. Saccharina seed spools were held in the hatchery from the last week of September 2022 until the first week of February 2023. After 8 weeks in the hatchery the temperature in the system housing the Saccharina seed spools was lowered to 4 ± 1°C and the irradiance lowered to 30 µmol m − 2 s − 1 for 12 h dark and 12 h light to deter further development of the sporophytes (Raymond and Stekoll 2021 ). Nereocystis seed spools were held in the hatchery from late December 2022 to the first week of February 2023 when they were outplanted at Alaska Ocean Farm’s Woody Island lease near Kodiak, AK. 2.3 Experimental farm system - The experimental farm was located on a commercial farm site permitted by the State of Alaska (Dead Humpy Creations, permit 2017-107-AF-WE). A farm design was developed that allowed experimentation with a variety of planting scenarios involving Nereocystis and Saccharina seeded lines. The compact arrangement is diagrammed in Fig. 1 , with 12 spreader-bar rigs each supporting ten 9.14 m, 1.0 cm diameter growlines spaced 0.38 m apart. The line color coding reveals our approach to the placement of pure and mixed cultures of the two species. 2.4 Seeding the lines - Seed was outplanted from a 7.6 m open skiff over a 2-day window when the air temperature was above 0°C to prevent damage from freezing. Nine seed spools were loaded onto a launching system that held the seed spools in the correct order by species on the experimental array as seen in Fig. 2 . The experimental array lines were then inserted through the seed spools on the launching system and attached at one end to the perpendicular array support lines via c-links. The seed line was tied securely to this end of the growline. The seed line was spooled off the seed spool and onto the growline by pulling the vessel down the lines manually in a perpendicular orientation to the array. Seed lines were wound around the growlines; the seed lines were cut and tied securely to the growline. The order and species of the nine seed spools was changed for each section of the array to match the map in Fig. 1 . 2.5 Monitoring, water quality, and management - Water sampling was done periodically throughout the study period. Temperature, salinity, and Secchi depth were recorded. Water samples were collected with a Niskin bottle, filtered and stored frozen until analyzed for nitrogen (NO 2 + NO 3 ). Nitrogen was quantified using a nitrate test kit (NECi Superior Enzymes). Light measurements with a LI-193 Spherical Quantum Sensor (LI-COR Environmental, Lincoln, Nebraska) were taken prior to harvest to assess light penetration below the Nereocystis canopy. A Spotter buoy (Sofar) was used to monitor waves, wave period, wind, and sea surface temperature at the farm site. The Spotter recorded waves and wind every 30 min and water temperature every hour from April to June 2023. 2.6 Harvest Harvest took place between 26–30 June 2023. Arrays were harvested line by line. Individual lines within each array were detached from the system and pulled into the harvest boat using a capstan. Kelp was cut from the growline and placed into a tote lined with a brailer bag. Holdfasts, stipes, and blades for each species were removed from the growlines. Once an entire line was harvested the brailer bag was weighed using a crane scale. Once weighed the brailer bag was emptied and the process started over again until all lines were weighed and removed from the system. 2.7 TEA analysis A techno-economic analysis (TEA) model previously developed in the context of MARINER research (Kite-Powell et al. 2022 ) was used to estimate the effect of the increase in yield per unit area and the change in input costs resulting from co-culture of two kelp species on the same longline array. The TEA model incorporates information about the unit cost of longline array components, deployment of the array, seeding, array management during grow out, and harvesting, to estimate the farmgate production cost of biomass at commercial scale (1,000 ha farmed footprint). 2.8 Statistical methods Statistical analysis was performed using R (version 4.3.3). The results were expressed as the mean ± standard error of the mean (SEM). A one-way analysis of variance (ANOVA, R function aov) was used to detect significant differences between treatments (systems, species, and lines). Tukey’s honest significant differences (HSD) were then computed for the pairwise comparisons. Normality of the data was assessed using a Shapiro-Wilk test. The level of significance used was p < 0.05 for all statistical tests. Results 3.1 Harvest weights 3.1.1 Relative yield per linear growline (kg m -1 ) The wet weights of the harvested thalli expressed as kg m -1 are shown in Fig. 3. The Saccharina yield from the combined array (5.7 ± 1.8 kg m -1 ) was almost the same as the yield of Saccharina from the Saccharina only array (6.2 ± 2.9 kg m -1 ). The values were not statistically different. However, the yield per meter for Nereocystis in the Combined arrays was almost twice that of the Nereocystis only arrays, 14.0 ± 3.2 vs 7.7 ± 3.6 kg m -1 . The difference was significant at the p<0.01 level. 3.1.2 Relative yield per growing area (kg m -2 ) The main thrust of this experiment was to determine if the yield per area would be different among the treatments. We compared the total weights of each of the arrays to each other (Fig. 4). The total yield per array for Nereocystis in the combined array was nearly the same as the total yield for the Nereocystis only (648 kg vs . 644 kg, n =4, 4, SE = 9.99,16.42, p= 0.46) even though the Nereocystis in the combined had 45% fewer growlines than the Nereocystis only (4 vs . 9 lines). Overall, the combined arrays yielded about 33% more biomass (30.51 kg m -2 , n=4, SE = 0.76) per array than the Nereocystis only (22.97 kg m -2 , n =4, SE = 0.59) and 67% more biomass per array than the Saccharina only (18.28 kg m -2 , N = 4, SE =2.22) arrays. 3.1.3 Differential Growth on the lines Each array consisted of 9 parallel lines, numbered 1-9. Lines #1 and 9 were on the outside at least 3 m away from the nearest array. The growth on these outside lines was generally more than the growth on the inner lines for all treatments (Fig. 5, Table 1). This indicates that the growth on the inner lines was reduced due to shading and/or poor nutrient availability. However, even though the lateral spacing was the same for all of the treatments, the combined treatment had better growth on all of the lines, both interior and exterior. Table 1 Yield (kg m -1 ) of the kelp species by line number. Lines 1 and 9 were on the outside of the arrays. Values are compared among the lines for each species in each column. Different letters denote significant differences (ANOVA: Tukey’s HSD test, p < 0.05). System Combined Nereocystis Only Saccharina Only Line # Nereocystis Saccharina Nereocystis Saccharina 1 16.01 ab 12.32 a 8.78 a 2 5.35 a 8.55 a 4.51 a 3 11.47 c 6.1 a 5.22 a 4 4.58 a 7.79 a 5.3 a 5 12.4 bc 5.84 a 5.63 a 6 5.05 a 6.38 a 4.8 a 7 12.32 bc 5.85 a 6.00 a 8 7.74 a 6.08 a 5.61 a 9 17.93 a 11.06 a 9.82 a 3.2 Temp/salinity/NOx/waves The salinity of the water around the farm from February to July was above 30 psu (Fig. 6). The water temperature at 3m depth stayed around 4 ℃ through the first part of April and then rose to about 9 ℃ by the first of July (Fig 6). The nitrogen concentration as nitrate + nitrite (NO x ) was over 20 µM in February and dropped to below 5 µM by the beginning of May (Fig 7), likely due to the onset of the spring bloom as indicated by the Secchi depth readings. However, the NO x concentration rebounded to over 7.5 µM by the first of July. This rebound is unusual for water in SE Alaska where the NO x concentration drops to less than 2 µM in the summer (Stekoll et al. 2021). Without more data it remains unknown what the NO x concentration trajectory is over the entire year at Kodiak. Light penetration below the Nereocystis canopy in the combined array dropped to less than 2% at one meter depth compared to the light just under the surface but increased to 14% at 4 m before dropping again. Average significant wave height, peak period, and wind (Fig. 8) were fairly constant throughout the study period, but more variability and higher maximum values were observed in April. Surface water temperatures steadily increased, but maximum temperatures were routinely higher than temperatures recorded at 3 m depth (10 ⁰C vs. 7.5 ⁰C in June, respectively). 3.3 TEA results The TEA model suggests that culture of a single kelp species at a 1,000 ha farmed footprint scale and with a wet harvest yield of 15 kg m -1 is possible at a production cost of $255 per dry tonne of Saccharina . Accounting for the 31% to 75% increase in yield reported here from co-culture of Nereocystis and Saccharina , and adjusting for reduced floatation on the growlines, the production cost decreases to $195 (-23%) and $147 (-43%) per dry tonne of biomass at the farmgate. Discussion 4.1 Ramifications 4.1.1 The results from this experiment that show an increase in kelp weight per unit area are encouraging for the future commercial production of biomass. Combining seaweeds that are buoyant with those that are not, makes use of more growing space in a farm. There are many ways to configure such a farm. In this research, we used close spacing of alternate species. This configuration allowed the buoyant kelps ( Nereocystis ) to move toward the surface while the negatively buoyant species ( Saccharina ) pulled the growlines down (Fig. 9 ). 4.1.2 Nereocystis and Saccharina line spacing Other ways to configure a two-kelp farm include seeding both species on each line, experimenting with the line spacing and line depth, and trying different species. One issue with seeding both species on each line is that the buoyant species may inhibit the growth of the other species by shading. We found that 92 to 97% of the light just below the surface was blocked at 2 m below a Nereocystis line. Another issue is maintaining an optimal line depth for both species. In our experience the negative buoyancy of the Saccharina was not nearly enough to compensate for the buoyancy of the Nereocystis growing at the same density, because as the Nereocystis grows it becomes even more buoyant. Adding 45 kg weights to one of the arrays provided only a temporary solution. We chose a line spacing of 38 cm arbitrarily based on the spacing used on our demonstration farm in Kodiak. There is likely a tradeoff between increasing spacing to enhance growth and minimizing spacing to increase density. Increasing the spacing could lead to better growth of both species, which may or may not increase the biomass per unit area. There may be a “sweet spot” in the line spacing where the biomass m − 2 would be at a maximum. Line depth is always a consideration in a kelp farm design. The optimum depth for Saccharina latissima has been found to be 2–4 m below the surface (Stekoll et al. 2021 ). But the best line depth for growing Nereocystis is unknown. In this research the Nereocystis pulled the lines up with the hollow bulbs reaching the surface while they were still relatively small and remained at the surface for the entire season. This resulted in damage to many, if not most, of the individuals due to bleaching from exposure at the surface (Fig. S1). Not only is it unknown how deep lines should be for the best growth of Nereocystis , but it may be that a different configuration would work better, such as fixing the lines at a certain depth above the bottom, simulating their natural habitat. The yields per square meter listed here should only be compared to each other. Due to the late outplanting date and the arbitrary line spacing, it is not practical to compare these results to other farms. The co-project with this study, funded by ARPA-E was designed to optimize biomass using Saccharina as the kelp of choice. The single species system was optimized over the course of 4 growing seasons (2019-23), with the highest yields of 4.95 kg m − 2 occurring during the 2020-21 season. 4.1.3 Techno-Economic Analysis Substantial reduction in per dry tonne farmgate production cost is possible with co-culture of two species such as Saccharina and Nereocystis . As noted above, results from the initial co-culture experiment found up to 75% increase in yield, which the TEA model suggests can drive production cost down to $ 147 per dry tonne. With further optimization of array configuration (line spacing) and higher yield from selective breeding, this may represent the most promising path to the goal of production cost below $ 100 per dry tonne. In particular, the TEA model suggests that the $ 100 production cost point can be reached with a further 50–60% increase in aggregate yield beyond the 75% improvement reported here. 4.2 Future needs 4.2.1 At this time, even though a number of researchers and farmers have been growing Nereocystis , we do not know how to grow it well. Current accumulated knowledge with respect to growing this species is summarized in Stephens et al. ( 2023 ). The lessons learned by this team related to the commercial farming of Saccharina may not apply to Nereocystis due in large part to the different morphologies and underwater weights of the two species. Being buoyant, when Nereocystis is grown on growlines, weight is needed to keep the plants from floating to the surface. With Saccharina , there is a need to keep the growlines at the intended depth, often requiring addition of flotation to the lines. Furthermore, unlike Saccharina that does well with a farm system that moves up and down with the tide, Nereocystis may respond better to a system that is a constant height off the bottom. This approach complicates matters of seeding, monitoring, maintaining growline tension, and harvest. The proposed rig shown in Fig. 10 supports an array of growlines strung between two catenary lines and tensioned by multiple opposing anchors. In this system, the four corner buoys are of variable displacement and can be used to bring the system to the surface for seeding, inspection, and harvest. Air is introduced into the buoys via an air hose such that the weights normally keeping the system at depth are lifted off the bottom. The approach is intended to mimic the normal tide-induced depth variations seen by natural Nereocystis beds. Such a Nereocystis farm system would also be suitable for Saccharina or for farming a combination of both species by alternating them from one growline to the next. By interconnecting those growlines across the farm at one or more places along the length, the buoyancy on one could help offset the weight of the other, offering operational advantages. 4.2.2 Density issues The seeding density of the kelps is another consideration for obtaining the optimal biomass. We seeded both species at 1,000 spores mL − 1 . This density has worked well for Saccharina (248 thalli m − 1 ) but appeared to be too dense (126 thalli m − 1 ) for Nereocystis when measured in June. This density of Nereocystis seeding resulted in many small, spindly thalli growing and entwining each other. The biomass of these individual plants was about 122 g compared to 1.6 kg from plants harvested in the wild (Stekoll et al. 2006 ). Some ways to adjust the density is by lowering the spore/seed density, spacing the location of the seed on the lines or by thinning the plants as they grow. 4.2.3 Surface exposure As mentioned above the Nereocystis plants become bleached if they remain at the surface. In natural Nereocystis beds the high tide will cover the bulbs, especially in places of high currents. The plants may be seen at the surface normally but will be submerged during the high tides. This periodic submergence likely protects the bulb from damage caused by exposure to the air and or the sun. Growing Nereocystis on suspended lines makes submerging the bulbs difficult. One way is to keep lowering the lines as the plants grow (Merrill and Gillingham 1991 ) or place the array a set distance above the bottom. Conclusion There is high potential to increase cultured kelp biomass per unit area by the co-culture of a floating and a negatively buoyant species. In Alaska there are several possible combinations of seaweeds that would be amenable to such an arrangement. Species that tend to be negatively buoyant and that have been successfully grown in Alaska are Alaria marginata , Saccharina latissima and Hedophyllum nigripes . Other potential species are Costaria costata , Cymathere triplicata and Agarum spp. Floating kelps in Alaska are Nereocystis luetkeana , Macrocystis spp and Eualaria fistulosa . In other regions of the world there are other candidates for floating seaweeds such as Ecklonia spp, Macrocystis spp, Pelagophycus porra , Durvillaea spp., Sargassum spp. and Fucus vesiculosus . These might be paired with regionally appropriate non-floating species, e.g. Lessonia spp, Undaria spp, Laminaria spp and Saccharina spp. There are also many types of configurations that could be used. In this research we used closely spaced lines, alternating species of each test species. Alternatively, in future work it may be possible to seed both species on the same line. Another major issue with the co-cultivation of two kelp species is finding the optimal method to grow the two species on one structure. Nereocystis is an ideal candidate from a biomass perspective, but it has proven problematic due to bleaching as it reaches the surface. Since other kelps such as Macrocystis and Eualaria do not have that issue in Alaska, they might be better in a co-cultivation system. Declarations Funding This work was supported by the United States Department of Energy Advanced Research Projects Agency-Energy (ARPA-E) Macroalgae Research Inspiring Novel Energy Resources (MARINER) award #DE-AR0000911 to the University of Alaska Fairbanks. Competing interests Financial interests: The authors declare they have no financial interests. Non-financial interests: none. Availability of data and material On publication data files will be available through ScholarWorks@UA (https://scholarworks.alaska.edu/), an open data repository. The datasets generated during and/or analyzed during the current study are also available from the corresponding author on reasonable request. Code availability Not applicable. Authors' contributions MS, SL, CY, LR, KB - Conceptualization MS, DB, AP, LM, CG, HK, SL, LR, KB - Methodology MS, DB - Formal analysis and investigation MS, DB, AP, LM, CG, HK, SL, LR, KB, CY - Writing - original draft preparation and review and editing MS, SL - Funding acquisition LR, KB - Resources MS - Supervision of Research, PI UAF Acknowledgments We are grateful for the in-kind contributions by GreenWave and C.A. Goudey & Associates. Logistic support was provided by the UAF Kodiak Seafood and Marine Science Center. References Augyte S, Yarish C, Redmond S, Kim JK (2017) Cultivation of a morphologically distinct strain of the sugar kelp, Saccharina latissima forma angustissima, from coastal Maine, USA, with implications for ecosystem services. J Appl Phycol 29:1967–1976. https://doi.org/10.1007/S10811-017-1102-X Brayden C, Coleman S (2023) Maine Seaweed Benchmarking Report. Maine Aquaculture Association. https://maineaqua.org/wp-content/uploads/2023/08/Maine-Seaweed-Benchmarking-Report.pdf Flavin N, Flavin K, Flahive B (2013) Kelp Farming Manual a Guide to the Processes, Techniques, and Equipment for Farming Kelp in New England Waters. Ocean Approved. https://www.researchgate.net/publication/311946411 Forbord S, Matsson S, Brodahl GE, Bluhm BA, Broch OJ, Handå A, Metaxas A, Skjermo J, Steinhovden KB, Olsen Y (2020) Latitudinal, seasonal and depth-dependent variation in growth, chemical composition and biofouling of cultivated Saccharina latissima (Phaeophyceae) along the Norwegian coast. J Appl Phycol 32:2215–2232. https://doi.org/10.1007/s10811-020-02038-y Gruenthal K, Habicht C (2022) Literature review for implementation of the 50-50 rule for cultivation of seaweeds and other aquatic plants in Alaska. Report number: RIR.2A.2022.01, Alaska Department of Fish and Game.https://www.researchgate.net/publication/371534772; accessed 12April 2024. Guillard RRL (1975) Culture of phytoplankton for feeding marine invertebrates. In: Smith WL, Chanley MH (Eds.) Culture of Marine Invertebrate Animals. Plenum Press, New York, USA. pp 26- 60. Hwang EK, Boo GH, Graf L, Yarish C, Yoon HS and Kim JK (2022) Kelps in Korea: from population structure to aquaculture to potential carbon sequestration. Algae 37:85-103. http://doi.org/10.4490/algae.2022.37.3.3. Jung JW, Pereira R, Yarish C, Kim JK (2024) Seaweed aquaculture: from cultivars to cultivation technologies to applications. In: Pereira R (ed) Aquaculture and living resource management, Volume 2. CRC Press (Taylor & Francis Group) Boca Raton. ISBN 978-1-032-34632-8. Kerrison PD, Stanley MS, Kelly M, MacLeod A, Black KD, Hughes AD (2016) Optimizing the settlement and hatchery culture of Saccharina latissima (Phaeophyta) by manipulation of growth medium and substrate surface condition. J Appl Phycol 28:1181–1191. https://doi.org/10.1007/S10811-015-0621-6 Kim JK, Stekoll M, Yarish C (2019) Opportunities, challenges and future directions of open-water seaweed aquaculture in the United States. Phycologia, 58: 446-461. DOI: 10.1080/00318884.2019.1625611 Kite-Powell HL, Ask E, Augyte S, Bailey D, Decker J, Goudey CA, Grebe G, Lic Y, Lindell S, Manganelli D, Marty-Rivera M, Ng C, Roberson L, Stekoll M, Umanzor S, Yarish C (2022) Estimating production cost for large-scale seaweed farms. Appl Phycol 3:435–445. https://doi.org/10.1080/26388081.2022.2111271 Li Y, Umanzor S, Ng C, Huang M, Marty-Rivera M, Bailey D, Aydlett M, Jannink J-L, Lindell S, Yarish C(2022) Skinny kelp ( Saccharina angustissima ) provides valuable genetics for the biomass improvement of farmed sugar kelp ( Saccharina latissima ). J Appl Phycol 34:2551–2563. https://doi.org/10.1007/s10811-022-02811-1 Merrill JE, Gillingham DM (1991) Bull Kelp Cultivation Handbook. National Coastal Resources Research and Development Institute, Portland. Ratcliff JJ, Soler-Vila A, Hanniffy D, Johnson MP, Edwards MD (2017). Optimisation of kelp ( Laminaria digitata ) gametophyte growth and gametogenesis: effects of photoperiod and culture media. J Appl Phycol 29:1957–1966. https://doi.org/10.1007/S10811-017-1070-1 Raymond AET, Stekoll MS (2021). Conditions for staggering and delaying outplantings of the kelps Saccharina latissima and Alaria marginata for mariculture. J World Aquacult Soc 52:1135–1157. https://doi.org/10.1111/jwas.12846 Redmond S, Green L, Yarish C, Kim J, Neefus C (2014) New England seaweed culture handbook. seaweed cultivation . Connecticut Sea Grant. https://opencommons.uconn.edu/seagrant_weedcult/1 Setthamongkol P, Tunkijjanukij S, Satapornvanit K, Salaenoi J (2015) Growth and nutrients analysis in marine macroalgae. Agriculture and Natural Resources 49:11–218. https://li01.tci-thaijo.org/index.php/anres/article/view/243563 Shea R, Chopin T (2007) Effects of germanium dioxide, an inhibitor of diatom growth, on the microscopic laboratory cultivation stage of the kelp, Laminaria saccharina . J Appl Phycol 19:27–32. https://doi.org/10.1007/s10811-006-9107-x Stekoll MS, Deysher LE, Hess M (2006) A remote sensing approach to estimating harvestable kelp biomass. J Appl Phycol 18:323-334. Stekoll MS, Peeples TN, Raymond AET (2021) Mariculture research of Macrocystis pyrifera and Saccharina latissima in southeast Alaska. J World Aquacult Soc 52:1031-1046. https://doi.org/10.1111/jwas.12765 Stephens T, Heifetz L, Stanley M (2023) Farming bull kelp: lessons learned and future considerations. Barnacle Foods, Juneau. https://docs.google.com/document/d/1vR4tTuYMizg9QVRuMXcIja7LYE0IX1_cy-un8O2jCZo/edit#heading=h.yaxs6rms40hi); accessed 12 April 2024. Additional Declarations No competing interests reported. Supplementary Files SupplementaryMaterial.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 09 May, 2024 Reviews received at journal 09 May, 2024 Reviews received at journal 08 May, 2024 Reviewers agreed at journal 20 Apr, 2024 Reviewers agreed at journal 18 Apr, 2024 Reviewers invited by journal 16 Apr, 2024 Editor assigned by journal 16 Apr, 2024 Submission checks completed at journal 16 Apr, 2024 First submitted to journal 13 Apr, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4263270","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":291693935,"identity":"f137e332-b5a0-4f95-9c19-ed176c950a2b","order_by":0,"name":"Michael Stekoll","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYNCCAwwyfOwNjAcYGBIYIBg/YGwAauFh4znAQKoWiQQitej2H3/+4MMZGx42yccPDvz4k8bAz55jgFeL2Y0cw8YZN9J42KTTDA72tuUwSPa8IaSFh7GZ58NhoJYEgwO8DRUMBjcI2XL++MPmPyAtksc/HPzzp4LBnqCWAwmGzQw3gFokeAyAZA6DgQQRfpnZcwboF56cgsOybWk8EmeeFRBy2IMPP47ZyPGzH9/48M2fZDn+9uQNeLVgAB7SlI+CUTAKRsEowAoA3cVNRupubo0AAAAASUVORK5CYII=","orcid":"","institution":"University of Alaska Fairbanks","correspondingAuthor":true,"prefix":"","firstName":"Michael","middleName":"","lastName":"Stekoll","suffix":""},{"id":291693937,"identity":"9439cb32-882d-4886-a99a-3abf2e332afb","order_by":1,"name":"Alf Pryor","email":"","orcid":"","institution":"Alaska Ocean Farms","correspondingAuthor":false,"prefix":"","firstName":"Alf","middleName":"","lastName":"Pryor","suffix":""},{"id":291693939,"identity":"5367b6ef-2a2a-47a4-a7ab-2f9cb6cd2494","order_by":2,"name":"Meyer Alexandra","email":"","orcid":"","institution":"Alaska Ocean Farms","correspondingAuthor":false,"prefix":"","firstName":"Meyer","middleName":"","lastName":"Alexandra","suffix":""},{"id":291693940,"identity":"52832aa6-d4d0-405c-b6b1-322fdcb399fc","order_by":3,"name":"Scott Lindell","email":"","orcid":"","institution":"Woods Hole Oceanographic Institution","correspondingAuthor":false,"prefix":"","firstName":"Scott","middleName":"","lastName":"Lindell","suffix":""},{"id":291693941,"identity":"6a2f54e2-6b27-4d1d-a3f1-416937e9c675","order_by":4,"name":"David Bailey","email":"","orcid":"","institution":"GreenWave","correspondingAuthor":false,"prefix":"","firstName":"David","middleName":"","lastName":"Bailey","suffix":""},{"id":291693942,"identity":"7824a731-6143-4a65-b1dc-233d4de74371","order_by":5,"name":"Hauke Kite-Powell","email":"","orcid":"","institution":"Woods Hole Oceanographic Institution","correspondingAuthor":false,"prefix":"","firstName":"Hauke","middleName":"","lastName":"Kite-Powell","suffix":""},{"id":291693943,"identity":"1c374195-ae7e-4fa0-bd70-a1ca9a895992","order_by":6,"name":"Cliff Goudey","email":"","orcid":"","institution":"CA Goudey \u0026 Associates","correspondingAuthor":false,"prefix":"","firstName":"Cliff","middleName":"","lastName":"Goudey","suffix":""},{"id":291693944,"identity":"50a0229e-b174-493b-a6ee-33d6c499b4fe","order_by":7,"name":"Loretta Roberson","email":"","orcid":"","institution":"Marine Biological Laboratory","correspondingAuthor":false,"prefix":"","firstName":"Loretta","middleName":"","lastName":"Roberson","suffix":""},{"id":291693945,"identity":"7346de9c-455b-44d4-b1c7-94585caefd32","order_by":8,"name":"Kendall Barbery","email":"","orcid":"","institution":"GreenWave","correspondingAuthor":false,"prefix":"","firstName":"Kendall","middleName":"","lastName":"Barbery","suffix":""},{"id":291693946,"identity":"f2a1d408-06c9-4674-a2a7-aed96f5ed89c","order_by":9,"name":"Charles Yarish","email":"","orcid":"","institution":"Woods Hole Oceanographic Institution","correspondingAuthor":false,"prefix":"","firstName":"Charles","middleName":"","lastName":"Yarish","suffix":""}],"badges":[],"createdAt":"2024-04-14 01:14:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4263270/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4263270/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54906298,"identity":"b794f757-dec2-48ac-8714-fcc3a1ceee79","added_by":"auto","created_at":"2024-04-18 11:43:35","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":174291,"visible":true,"origin":"","legend":"\u003cp\u003eA plan and side view of the experimental farm showing arrangement of the seeded lines\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/82c51caf99803bc72c01b3a5.png"},{"id":54905895,"identity":"ca23bd2c-f343-4482-9a3c-4c33b787cb73","added_by":"auto","created_at":"2024-04-18 11:35:35","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":582437,"visible":true,"origin":"","legend":"\u003cp\u003eLoading seed spools onto the launching system. Photo by Alf Pryor\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/1c2f9f3e3c2d0c7456bff378.png"},{"id":54905891,"identity":"fc0bdf8c-9f52-4232-a1a0-26416c3505a6","added_by":"auto","created_at":"2024-04-18 11:35:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":61596,"visible":true,"origin":"","legend":"\u003cp\u003eYield of kelps on the experimental farm at Woody Island shown as a boxplot. The yield is expressed as kg m\u003csup\u003e-1\u003c/sup\u003e for the three treatments separated by species.\u0026nbsp; Different letters denote significant differences (Tukey’s HSD; p \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/f97b295c34aac69c776f21ba.png"},{"id":54905892,"identity":"a967867c-dd3a-4066-bbd8-9e4a8e72751a","added_by":"auto","created_at":"2024-04-18 11:35:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":45719,"visible":true,"origin":"","legend":"\u003cp\u003eYield of kelps on the experimental farm at Woody Island shown as a boxplot. The yield is expressed as kg m\u003csup\u003e-2\u003c/sup\u003e per array type. Different letters denote significant differences (Tukey’s HSD; p \u0026lt; 0.05)\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/677e5e856f8c75f24971593e.png"},{"id":54906881,"identity":"9ba88117-c952-4723-9923-919049a86973","added_by":"auto","created_at":"2024-04-18 11:51:35","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":59953,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/1f92712154127bdf350c6234.png"},{"id":54906882,"identity":"e909deb2-c2ba-42ac-9e29-152f1b09dbcd","added_by":"auto","created_at":"2024-04-18 11:51:35","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":29849,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature and salinity trends at 3m deep near Woody Island, Kodiak, Alaska\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/d8be6d241eefd7806fc503a0.png"},{"id":54905896,"identity":"8e13d41e-59f8-4645-ae2d-fd07119e4da4","added_by":"auto","created_at":"2024-04-18 11:35:35","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":36701,"visible":true,"origin":"","legend":"\u003cp\u003eNOx concentration at 2 m depth and Secchi depth near Woody Island, Kodiak, Alaska\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/b4ce324cab49a4647a50c1da.png"},{"id":54905901,"identity":"90bf001e-4388-4b2e-a678-ac4a3702e33a","added_by":"auto","created_at":"2024-04-18 11:35:35","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":237743,"visible":true,"origin":"","legend":"\u003cp\u003eSignificant wave height, peak wave period, wind speed, and sea surface temperature recorded by the Spotter buoy at Woody Island, Kodiak, Alaska\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/0b3a7ed90cd01278efda6245.png"},{"id":54905902,"identity":"4d35d8e5-a87f-4f01-b6f8-cd8cdc213037","added_by":"auto","created_at":"2024-04-18 11:35:36","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":543878,"visible":true,"origin":"","legend":"\u003cp\u003ePhoto of the array in June 2023 showing that \u003cem\u003eSaccharina \u003c/em\u003e(S) and \u003cem\u003eNereocystis \u003c/em\u003e(N) have increased their vertical spacing from the original horizontal line spacing of 38 cm. This allows more use of the water column, increasing light availability and nutrient access. The \u003cem\u003eSaccharina \u003c/em\u003ehas sunk to about 3.7 m below the surface, which remains in the optimal depth range for growth of this species in Alaska (Stekoll et al. 2021). Photo by David Bailey\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/25e78086cdf1aab4da3e1c84.png"},{"id":54905900,"identity":"a2128785-d538-447e-8fbd-a22d00daec1e","added_by":"auto","created_at":"2024-04-18 11:35:35","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":181454,"visible":true,"origin":"","legend":"\u003cp\u003eA commercial-scale farm system designed for \u003cem\u003eNereocystis.\u003c/em\u003e Diagram by Goudey \u0026amp; Associates, Newburyport, MA\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/f91b3a452fce43fef83b8f3e.png"},{"id":54907276,"identity":"bd617b48-1265-4ebb-9b13-6d3690dcc44b","added_by":"auto","created_at":"2024-04-18 11:59:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2743035,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/b4c20b51-a17b-4ea8-9b69-a0c0213153e5.pdf"},{"id":54906300,"identity":"c7c87eee-b341-4d37-9e2d-f3c9123ee0f1","added_by":"auto","created_at":"2024-04-18 11:43:35","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":433318,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-4263270/v1/9fcc54660268f58c11fe49b4.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimizing Seaweed Biomass Production - A Two Kelp Solution","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe mariculture of seaweed in Alaska, like much of the US, is less than a decade old (Kim et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). A kelp farming demonstration project was initiated in 2019 funded by the US Department of Energy\u0026rsquo;s MARINER Program whose focus was maximizing yield per lease area by examining how practically and closely cultivation lines can be spaced on an interconnected array to grow \u003cem\u003eSaccharina latissima\u003c/em\u003e (sugar kelp) (hereafter as \u003cem\u003eSaccharina\u003c/em\u003e). Results from three years of farm trials showed that spacing cultivation lines by as little as 0.76\u0026ndash;0.85 m does not negatively affect the yield of \u003cem\u003eSaccharina\u003c/em\u003e per meter of line. The yield varied each year between 6 and 9 kg m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is similar to average yields of farmed \u003cem\u003eSaccharina\u003c/em\u003e on independent lines as reported in the Northeastern US (Brayden and Coleman \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) and Europe (Forbord et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, it is considerably lower than potential yields found in the farmed congeneric species, Asian kombu (\u003cem\u003eSaccharina japonica\u003c/em\u003e), which, after more than 40 years of selective breeding, nears 30 kg m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Hwang et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2022\u003c/span\u003e, Jung et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOne of the goals of the Department of Energy\u0026rsquo;s MARINER Program is to reduce the cost of production of seaweed to less than \u003cspan\u003e$\u003c/span\u003e100 per dry metric ton in order for it to be competitive with other land-based crops used as biofuel feedstocks. Our techno-economic analysis of kelp farming shows that yield per unit area is the major driving force for lowering the cost of production (Kite-Powell et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). A sugar kelp genetic selection and breeding program could eventually match the relative yield of Asian kombu by developing high-yield strains. Indeed, in the Northeast US a MARINER funded breeding program for sugar kelp has achieved marked improvements in yield (Li et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) with an average over 10 kg m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and a single cross yielding 28 kg m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. However, current regulations in Alaska require that kelp seedlings come from random mating of meiospores from 50 wild individuals collected from within 50 km of the farm site. Because selective breeding is effectively outlawed in Alaska, we examined ways to markedly increase yield by more fully using the water column with the co-culture of negatively buoyant \u003cem\u003eSaccharina\u003c/em\u003e and another floating kelp species.\u003c/p\u003e \u003cp\u003eThe premise for this co-culture project was that the floating kelps, growing near or on the same line, will not compete significantly with \u003cem\u003eSaccharina.\u003c/em\u003e Each species will occupy its own vertical space so that there will not be competition for space, nutrients or light for the first few months of growth. The only issue might be competition for light when the kelps get larger in the last month of the growing season, and as they approach harvest size. We hypothesized that the overall yield of these co-culture systems will be significantly more than the yield of either crop grown alone. A further benefit is that the floatation provided by the floating kelps may offset the need to add buoyancy to the \u003cem\u003eSaccharina\u003c/em\u003e longlines prevent sagging.\u003c/p\u003e \u003cp\u003eIn Alaska there are three species of floating kelps: \u003cem\u003eMacrocystis integrifolia\u003c/em\u003e (giant kelp), \u003cem\u003eNereocystis luetkeana\u003c/em\u003e (bull kelp) (hereafter as \u003cem\u003eNereocystis\u003c/em\u003e), and \u003cem\u003eEualaria fistulosa\u003c/em\u003e (dragon kelp). Currently, \u003cem\u003eNereocystis\u003c/em\u003e already has commercial value as a food source, but wild harvests cannot keep up with demand. Several organizations have grown \u003cem\u003eNereocystis\u003c/em\u003e with mixed success (Stephens et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Recent work in California grew \u003cem\u003eNereocystis\u003c/em\u003e with wet weights greater than 16 kg m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e on a five-line array (K. Barbery, personal communication). Using information from that and other projects we designed a demonstration project to incorporate growing both \u003cem\u003eSaccharina\u003c/em\u003e and \u003cem\u003eNereocystis\u003c/em\u003e side by side on 9-line arrays to determine if increased yields could result from using a two-crop system. To our knowledge, this is the first publication to report on floating and hanging kelps farmed in close proximity.\u003c/p\u003e"},{"header":"Materials \u0026 Methods","content":"\u003cp\u003e \u003cb\u003e2.1 Collecting parent material\u003c/b\u003e - \u003cem\u003eNereocystis\u003c/em\u003e and \u003cem\u003eSaccharina\u003c/em\u003e seed for the project was produced in the Blue Evolution Hatchery housed at the Kodiak Fisheries Research Science Center in Kodiak, AK (permit 2017-104-HA-WE). Sorus tissue was collected from 50 wild \u003cem\u003eSaccharina\u003c/em\u003e in late September 2022 from Trident Basin near Kodiak, AK, and \u003cem\u003eNereocystis\u003c/em\u003e in December 2022 from the coastline adjacent to the Alaska Ocean Farms Woody Island lease in Kodiak. Sori were collected via Alaska Department of Fish and Game protocol to create a meiospore solution with a concentration of 1,000 spores mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of sanitized seawater (Gruenthal et al. 2022). Seawater from Trident Basin was filtered via sand filtration, then sanitized by mechanical filtering down to 0.5 \u0026micro; and then passed through an ultraviolet water sterilizer (Redmond et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Sori were cleaned of surface contamination and other organisms by wiping with a clean paper towel. Sori were then soaked for one minute in a solution of 4% iodine and sanitized seawater, rinsed in sanitized seawater, and dried with paper towels (Augyte et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Cleaned, dried sori were then placed in layers of dry paper towel and stored in sealed plastic bags at 4\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C and total darkness for 24 hours in a laboratory fridge (Flavin et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e \u003cb\u003e2.2 Hatchery procedure\u003c/b\u003e - After 24 hours the sori were removed from cold storage and placed in 1,000 mL beakers of sanitized seawater. The beakers were stored at 11\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C, exposed to 60 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e irradiance, and checked for meiospore release every 30 minutes (Redmond et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Meiospore release was verified by examining a 1 mL water sample from the release beakers via microscopy for motile meiospores. Meiospore density per mL seawater was counted using a hemocytometer. Stocking density was calculated using the following formula: VMS\u0026thinsp;=\u0026thinsp;DSC/(RWC/VSA), where VMS is the volume meiospore solution needed for stocking aquaria at 1,000 meiospores mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, DSC is the desired stocking concentration of meiospores (1,000 spores mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), RWC is the release water concentration of meiospores (spores mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and VSA is the volume of seawater in the aquaria (Flavin et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). This process was repeated for three days until sufficient meiospore release was observed to produce 1,000 spores mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e seawater in the hatchery aquaria.\u003c/p\u003e \u003cp\u003eThe calculated volume of release water was added to the hatchery aquaria containing the seed spools. Seed spools were composed of 7.62 cm diameter x 23 cm sections of PVC pipe with ~\u0026thinsp;61 m of 1.5 mm nylon string (Holdfast\u0026reg; Tufting Twine, Ludlow\u0026reg; Series, A\u0026amp;E Industrial Textiles) wound round the exterior. Germanium dioxide (GeO\u003csub\u003e2\u003c/sub\u003e) in a deionized water solution was added to the tanks to achieve a concentration of 0.002 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to deter diatom growth (Shea et al. 2007). F/2 seawater medium (parts A and B) (Guillard \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1975\u003c/span\u003e) was added to the tanks to achieve a volume of 0.29 mL L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to encourage spore settlement and gametophyte development (Ratcliff et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Setthamongkol et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The spools were left in total darkness at 11\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C for 24 hours (Kerrison et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). After 24 hours the spools were transferred to the main hatchery and illuminated with fluorescent lighting with an irradiance of 30 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 12 h dark and 12 h light and a temp of 11\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C (Redmond et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Irradiance was increased by 15 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e per week for 2 weeks and then held at 60 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for the duration of hatchery cultivation (Augyte et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The seawater in the aquaria was drained and replenished 2x per week during the hatchery period. During water changes both GeO\u003csub\u003e2\u003c/sub\u003e and F/2 were replenished in the aquaria at the same concentrations as during stocking to deter diatom recruitment and promote sporophyte growth.\u003c/p\u003e \u003cp\u003e \u003cem\u003eSaccharina\u003c/em\u003e seed spools were held in the hatchery from the last week of September 2022 until the first week of February 2023. After 8 weeks in the hatchery the temperature in the system housing the \u003cem\u003eSaccharina\u003c/em\u003e seed spools was lowered to 4\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C and the irradiance lowered to 30 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 12 h dark and 12 h light to deter further development of the sporophytes (Raymond and Stekoll \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). \u003cem\u003eNereocystis\u003c/em\u003e seed spools were held in the hatchery from late December 2022 to the first week of February 2023 when they were outplanted at Alaska Ocean Farm\u0026rsquo;s Woody Island lease near Kodiak, AK.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.3 Experimental farm system\u003c/b\u003e - The experimental farm was located on a commercial farm site permitted by the State of Alaska (Dead Humpy Creations, permit 2017-107-AF-WE). A farm design was developed that allowed experimentation with a variety of planting scenarios involving \u003cem\u003eNereocystis\u003c/em\u003e and \u003cem\u003eSaccharina\u003c/em\u003e seeded lines. The compact arrangement is diagrammed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, with 12 spreader-bar rigs each supporting ten 9.14 m, 1.0 cm diameter growlines spaced 0.38 m apart. The line color coding reveals our approach to the placement of pure and mixed cultures of the two species.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.4 Seeding the lines\u003c/b\u003e - Seed was outplanted from a 7.6 m open skiff over a 2-day window when the air temperature was above 0\u0026deg;C to prevent damage from freezing. Nine seed spools were loaded onto a launching system that held the seed spools in the correct order by species on the experimental array as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The experimental array lines were then inserted through the seed spools on the launching system and attached at one end to the perpendicular array support lines via c-links. The seed line was tied securely to this end of the growline. The seed line was spooled off the seed spool and onto the growline by pulling the vessel down the lines manually in a perpendicular orientation to the array. Seed lines were wound around the growlines; the seed lines were cut and tied securely to the growline. The order and species of the nine seed spools was changed for each section of the array to match the map in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e \u003cb\u003e2.5 Monitoring, water quality, and management\u003c/b\u003e -\u003c/p\u003e \u003cp\u003eWater sampling was done periodically throughout the study period. Temperature, salinity, and Secchi depth were recorded. Water samples were collected with a Niskin bottle, filtered and stored frozen until analyzed for nitrogen (NO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;NO\u003csub\u003e3\u003c/sub\u003e). Nitrogen was quantified using a nitrate test kit (NECi Superior Enzymes). Light measurements with a LI-193 Spherical Quantum Sensor (LI-COR Environmental, Lincoln, Nebraska) were taken prior to harvest to assess light penetration below the \u003cem\u003eNereocystis\u003c/em\u003e canopy. A Spotter buoy (Sofar) was used to monitor waves, wave period, wind, and sea surface temperature at the farm site. The Spotter recorded waves and wind every 30 min and water temperature every hour from April to June 2023.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Harvest\u003c/h2\u003e \u003cp\u003eHarvest took place between 26\u0026ndash;30 June 2023. Arrays were harvested line by line. Individual lines within each array were detached from the system and pulled into the harvest boat using a capstan. Kelp was cut from the growline and placed into a tote lined with a brailer bag. Holdfasts, stipes, and blades for each species were removed from the growlines. Once an entire line was harvested the brailer bag was weighed using a crane scale. Once weighed the brailer bag was emptied and the process started over again until all lines were weighed and removed from the system.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.7 TEA analysis\u003c/h2\u003e \u003cp\u003eA techno-economic analysis (TEA) model previously developed in the context of MARINER research (Kite-Powell et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) was used to estimate the effect of the increase in yield per unit area and the change in input costs resulting from co-culture of two kelp species on the same longline array. The TEA model incorporates information about the unit cost of longline array components, deployment of the array, seeding, array management during grow out, and harvesting, to estimate the farmgate production cost of biomass at commercial scale (1,000 ha farmed footprint).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.8 Statistical methods\u003c/h2\u003e \u003cp\u003eStatistical analysis was performed using R (version 4.3.3). The results were expressed as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard error of the mean (SEM). A one-way analysis of variance (ANOVA, R function aov) was used to detect significant differences between treatments (systems, species, and lines). Tukey\u0026rsquo;s honest significant differences (HSD) were then computed for the pairwise comparisons. Normality of the data was assessed using a Shapiro-Wilk test. The level of significance used was p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for all statistical tests.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003e3.1 Harvest weights\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e3.1.1 Relative yield per linear growline (kg m\u003csup\u003e-1\u003c/sup\u003e)\u003c/p\u003e\n\u003cp\u003eThe wet weights of the harvested thalli expressed as kg m\u003csup\u003e-1\u003c/sup\u003e are shown in Fig. 3. \u0026nbsp;The \u003cem\u003eSaccharina\u003c/em\u003e yield from the combined array (5.7 \u0026plusmn; 1.8 kg m\u003csup\u003e-1\u003c/sup\u003e) was almost the same as the yield of \u003cem\u003eSaccharina\u003c/em\u003e from the \u003cem\u003eSaccharina\u003c/em\u003e only array (6.2 \u0026plusmn; 2.9 kg m\u003csup\u003e-1\u003c/sup\u003e). \u0026nbsp;The values were not statistically different. \u0026nbsp;However, the yield per meter for \u003cem\u003eNereocystis\u003c/em\u003e in the Combined arrays was almost twice that of the \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003eonly arrays, 14.0 \u0026plusmn; 3.2 \u003cem\u003evs\u0026nbsp;\u003c/em\u003e7.7 \u0026plusmn; 3.6 kg m\u003csup\u003e-1\u003c/sup\u003e. \u0026nbsp;The difference was significant at the p\u0026lt;0.01 level.\u003c/p\u003e\n\u003cp\u003e3.1.2 Relative yield per growing area (kg m\u003csup\u003e-2\u003c/sup\u003e)\u003c/p\u003e\n\u003cp\u003eThe main thrust of this experiment was to determine if the yield per area would be different among the treatments. \u0026nbsp;We compared the total weights of each of the arrays to each other (Fig. 4). \u0026nbsp;The total yield per array for \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003ein the combined array was nearly the same as the total yield for the \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003eonly (648 kg \u003cem\u003evs\u003c/em\u003e. 644 kg, n =4, 4, SE = 9.99,16.42, p= 0.46) even though the \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003ein the combined had 45% fewer growlines than the \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003eonly (4 \u003cem\u003evs\u003c/em\u003e. 9 lines). \u0026nbsp;Overall, the\u003cem\u003e\u0026nbsp;\u003c/em\u003ecombined arrays yielded about 33% more biomass (30.51 kg m\u003csup\u003e-2\u003c/sup\u003e, n=4, SE = 0.76) per array than the \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003eonly (22.97 kg m\u003csup\u003e-2\u003c/sup\u003e, n =4, SE = 0.59) and 67% more biomass per array than the \u003cem\u003eSaccharina\u0026nbsp;\u003c/em\u003eonly (18.28 kg m\u003csup\u003e-2\u003c/sup\u003e, N = 4, SE =2.22) arrays.\u003c/p\u003e\n\u003cp\u003e3.1.3 Differential Growth on the lines\u003c/p\u003e\n\u003cp\u003eEach array consisted of 9 parallel lines, numbered 1-9. \u0026nbsp;Lines #1 and 9 were on the outside at least 3 m away from the nearest array. \u0026nbsp;The growth on these outside lines was generally more than the growth on the inner lines for all treatments (Fig. 5, Table 1). This indicates that the growth on the inner lines was reduced due to shading and/or poor nutrient availability. However, even though the lateral spacing was the same for all of the treatments, the combined treatment had better growth on all of the lines, both interior and exterior.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Yield (kg m\u003csup\u003e-1\u003c/sup\u003e) of the kelp species by line number. \u0026nbsp;Lines 1 and 9 were on the outside of the arrays. \u0026nbsp;Values are compared among the lines for each species in each column.\u0026nbsp;Different letters denote significant differences\u0026nbsp;(ANOVA: Tukey\u0026rsquo;s HSD test, p \u0026lt; 0.05).\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"17.045454545454547%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"37.5%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp;System Combined\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e\u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003eOnly\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e\u003cem\u003eSaccharina\u0026nbsp;\u003c/em\u003eOnly\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003eLine #\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003eNereocystis\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e\u003cem\u003eSaccharina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e\u003cem\u003eNereocystis\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e\u003cem\u003eSaccharina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\n \u003cp\u003e16.01\u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e12.32\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e8.78\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.35\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e8.55\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e4.51\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\n \u003cp\u003e11.47\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e6.1\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.22\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e4.58\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e7.79\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.3\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\n \u003cp\u003e12.4\u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.84\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.63\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.05\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e6.38\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e4.8\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\n \u003cp\u003e12.32\u003csup\u003ebc\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.85\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e6.00\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e7.74\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e6.08\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e5.61\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.454545454545453%\" colspan=\"2\"\u003e\n \u003cp\u003e17.93\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e11.06\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"22.727272727272727%\"\u003e\n \u003cp\u003e9.82\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Temp/salinity/NOx/waves\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe salinity of the water around the farm from February to July was above 30 psu (Fig. 6). \u0026nbsp;The water temperature at 3m depth stayed around 4 ℃ through the first part of April and then rose to about 9 ℃ by the first of July (Fig 6). \u0026nbsp;The nitrogen concentration as nitrate + nitrite (NO\u003csub\u003ex\u003c/sub\u003e) was over 20 \u0026micro;M in February and dropped to below 5 \u0026micro;M by the beginning of May (Fig 7), likely due to the onset of the spring bloom as indicated by the Secchi depth readings. \u0026nbsp;However, the NO\u003csub\u003ex\u003c/sub\u003e concentration rebounded to over 7.5 \u0026micro;M by the first of July. This rebound is unusual for water in SE Alaska where the NO\u003csub\u003ex\u003c/sub\u003e concentration drops to less than 2 \u0026micro;M in the summer (Stekoll et al. 2021). \u0026nbsp;Without more data it remains unknown what the NO\u003csub\u003ex\u003c/sub\u003e concentration trajectory is over the entire year at Kodiak.\u003c/p\u003e\n\u003cp\u003eLight penetration below the \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003ecanopy in the combined array dropped to less than 2% at one meter depth compared to the light just under the surface but increased to 14% at 4 m before dropping again.\u003c/p\u003e\n\u003cp\u003eAverage significant wave height, peak period, and wind (Fig. 8) were fairly constant throughout the study period, but more variability and higher maximum values were observed in April. Surface water temperatures steadily increased, but maximum temperatures were routinely higher than temperatures recorded at 3 m depth (10 ⁰C vs. 7.5 ⁰C in June, respectively).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 TEA results\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe TEA model suggests that culture of a single kelp species at a 1,000 ha farmed footprint scale and with a wet harvest yield of 15 kg m\u003csup\u003e-1\u003c/sup\u003e is possible at a production cost of $255 per dry tonne of \u003cem\u003eSaccharina\u003c/em\u003e. \u0026nbsp;Accounting for the 31% to 75% increase in yield reported here from co-culture of \u003cem\u003eNereocystis\u0026nbsp;\u003c/em\u003eand \u003cem\u003eSaccharina\u003c/em\u003e, and adjusting for reduced floatation on the growlines, the production cost decreases to $195 (-23%) and $147 (-43%) per dry tonne of biomass at the farmgate.\u0026nbsp;\u003c/p\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Ramifications\u003c/h2\u003e \u003cp\u003e4.1.1 The results from this experiment that show an increase in kelp weight per unit area are encouraging for the future commercial production of biomass. Combining seaweeds that are buoyant with those that are not, makes use of more growing space in a farm. There are many ways to configure such a farm. In this research, we used close spacing of alternate species. This configuration allowed the buoyant kelps (\u003cem\u003eNereocystis\u003c/em\u003e) to move toward the surface while the negatively buoyant species (\u003cem\u003eSaccharina\u003c/em\u003e) pulled the growlines down (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e4.1.2 \u003cem\u003eNereocystis\u003c/em\u003e and \u003cem\u003eSaccharina\u003c/em\u003e line spacing\u003c/p\u003e \u003cp\u003eOther ways to configure a two-kelp farm include seeding both species on each line, experimenting with the line spacing and line depth, and trying different species. One issue with seeding both species on each line is that the buoyant species may inhibit the growth of the other species by shading. We found that 92 to 97% of the light just below the surface was blocked at 2 m below a \u003cem\u003eNereocystis\u003c/em\u003e line. Another issue is maintaining an optimal line depth for both species. In our experience the negative buoyancy of the \u003cem\u003eSaccharina\u003c/em\u003e was not nearly enough to compensate for the buoyancy of the \u003cem\u003eNereocystis\u003c/em\u003e growing at the same density, because as the \u003cem\u003eNereocystis\u003c/em\u003e grows it becomes even more buoyant. Adding 45 kg weights to one of the arrays provided only a temporary solution.\u003c/p\u003e \u003cp\u003eWe chose a line spacing of 38 cm arbitrarily based on the spacing used on our demonstration farm in Kodiak. There is likely a tradeoff between increasing spacing to enhance growth and minimizing spacing to increase density. Increasing the spacing could lead to better growth of both species, which may or may not increase the biomass per unit area. There may be a \u0026ldquo;sweet spot\u0026rdquo; in the line spacing where the biomass m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e would be at a maximum.\u003c/p\u003e \u003cp\u003eLine depth is always a consideration in a kelp farm design. The optimum depth for \u003cem\u003eSaccharina latissima\u003c/em\u003e has been found to be 2\u0026ndash;4 m below the surface (Stekoll et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). But the best line depth for growing \u003cem\u003eNereocystis\u003c/em\u003e is unknown. In this research the \u003cem\u003eNereocystis\u003c/em\u003e pulled the lines up with the hollow bulbs reaching the surface while they were still relatively small and remained at the surface for the entire season. This resulted in damage to many, if not most, of the individuals due to bleaching from exposure at the surface (Fig. S1). Not only is it unknown how deep lines should be for the best growth of \u003cem\u003eNereocystis\u003c/em\u003e, but it may be that a different configuration would work better, such as fixing the lines at a certain depth above the bottom, simulating their natural habitat.\u003c/p\u003e\u003cp\u003eThe yields per square meter listed here should only be compared to each other. Due to the late outplanting date and the arbitrary line spacing, it is not practical to compare these results to other farms. The co-project with this study, funded by ARPA-E was designed to optimize biomass using \u003cem\u003eSaccharina\u003c/em\u003e as the kelp of choice. The single species system was optimized over the course of 4 growing seasons (2019-23), with the highest yields of 4.95 kg m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e occurring during the 2020-21 season.\u003c/p\u003e \u003cp\u003e4.1.3 Techno-Economic Analysis\u003c/p\u003e \u003cp\u003eSubstantial reduction in per dry tonne farmgate production cost is possible with co-culture of two species such as \u003cem\u003eSaccharina\u003c/em\u003e and \u003cem\u003eNereocystis\u003c/em\u003e. As noted above, results from the initial co-culture experiment found up to 75% increase in yield, which the TEA model suggests can drive production cost down to \u003cspan\u003e$\u003c/span\u003e147 per dry tonne. With further optimization of array configuration (line spacing) and higher yield from selective breeding, this may represent the most promising path to the goal of production cost below \u003cspan\u003e$\u003c/span\u003e100 per dry tonne. In particular, the TEA model suggests that the \u003cspan\u003e$\u003c/span\u003e100 production cost point can be reached with a further 50\u0026ndash;60% increase in aggregate yield beyond the 75% improvement reported here.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Future needs\u003c/h2\u003e \u003cp\u003e4.2.1 At this time, even though a number of researchers and farmers have been growing \u003cem\u003eNereocystis\u003c/em\u003e, we do not know how to grow it well. Current accumulated knowledge with respect to growing this species is summarized in Stephens et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The lessons learned by this team related to the commercial farming of \u003cem\u003eSaccharina\u003c/em\u003e may not apply to \u003cem\u003eNereocystis\u003c/em\u003e due in large part to the different morphologies and underwater weights of the two species. Being buoyant, when \u003cem\u003eNereocystis\u003c/em\u003e is grown on growlines, weight is needed to keep the plants from floating to the surface. With \u003cem\u003eSaccharina\u003c/em\u003e, there is a need to keep the growlines at the intended depth, often requiring addition of flotation to the lines. Furthermore, unlike \u003cem\u003eSaccharina\u003c/em\u003e that does well with a farm system that moves up and down with the tide, \u003cem\u003eNereocystis\u003c/em\u003e may respond better to a system that is a constant height off the bottom. This approach complicates matters of seeding, monitoring, maintaining growline tension, and harvest.\u003c/p\u003e \u003cp\u003eThe proposed rig shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003e supports an array of growlines strung between two catenary lines and tensioned by multiple opposing anchors. In this system, the four corner buoys are of variable displacement and can be used to bring the system to the surface for seeding, inspection, and harvest. Air is introduced into the buoys via an air hose such that the weights normally keeping the system at depth are lifted off the bottom. The approach is intended to mimic the normal tide-induced depth variations seen by natural \u003cem\u003eNereocystis\u003c/em\u003e beds.\u003c/p\u003e\u003cp\u003eSuch a \u003cem\u003eNereocystis\u003c/em\u003e farm system would also be suitable for \u003cem\u003eSaccharina\u003c/em\u003e or for farming a combination of both species by alternating them from one growline to the next. By interconnecting those growlines across the farm at one or more places along the length, the buoyancy on one could help offset the weight of the other, offering operational advantages.\u003c/p\u003e \u003cp\u003e4.2.2 Density issues\u003c/p\u003e \u003cp\u003eThe seeding density of the kelps is another consideration for obtaining the optimal biomass. We seeded both species at 1,000 spores mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This density has worked well for \u003cem\u003eSaccharina\u003c/em\u003e (248 thalli m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) but appeared to be too dense (126 thalli m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) for \u003cem\u003eNereocystis\u003c/em\u003e when measured in June. This density of \u003cem\u003eNereocystis\u003c/em\u003e seeding resulted in many small, spindly thalli growing and entwining each other. The biomass of these individual plants was about 122 g compared to 1.6 kg from plants harvested in the wild (Stekoll et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Some ways to adjust the density is by lowering the spore/seed density, spacing the location of the seed on the lines or by thinning the plants as they grow.\u003c/p\u003e \u003cp\u003e4.2.3 Surface exposure\u003c/p\u003e \u003cp\u003eAs mentioned above the \u003cem\u003eNereocystis\u003c/em\u003e plants become bleached if they remain at the surface. In natural \u003cem\u003eNereocystis\u003c/em\u003e beds the high tide will cover the bulbs, especially in places of high currents. The plants may be seen at the surface normally but will be submerged during the high tides. This periodic submergence likely protects the bulb from damage caused by exposure to the air and or the sun. Growing \u003cem\u003eNereocystis\u003c/em\u003e on suspended lines makes submerging the bulbs difficult. One way is to keep lowering the lines as the plants grow (Merrill and Gillingham \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1991\u003c/span\u003e) or place the array a set distance above the bottom.\u003c/p\u003e \u003c/div\u003e "},{"header":"Conclusion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003cp\u003eThere is high potential to increase cultured kelp biomass per unit area by the co-culture of a floating and a negatively buoyant species. In Alaska there are several possible combinations of seaweeds that would be amenable to such an arrangement. Species that tend to be negatively buoyant and that have been successfully grown in Alaska are \u003cem\u003eAlaria marginata\u003c/em\u003e, \u003cem\u003eSaccharina latissima\u003c/em\u003e and \u003cem\u003eHedophyllum nigripes\u003c/em\u003e. Other potential species are \u003cem\u003eCostaria costata\u003c/em\u003e, \u003cem\u003eCymathere triplicata\u003c/em\u003e and \u003cem\u003eAgarum\u003c/em\u003e spp. Floating kelps in Alaska are \u003cem\u003eNereocystis luetkeana\u003c/em\u003e, \u003cem\u003eMacrocystis\u003c/em\u003e spp and \u003cem\u003eEualaria fistulosa\u003c/em\u003e. In other regions of the world there are other candidates for floating seaweeds such as \u003cem\u003eEcklonia\u003c/em\u003e spp, \u003cem\u003eMacrocystis\u003c/em\u003e spp, \u003cem\u003ePelagophycus porra\u003c/em\u003e, \u003cem\u003eDurvillaea\u003c/em\u003e spp., \u003cem\u003eSargassum\u003c/em\u003e spp. and \u003cem\u003eFucus vesiculosus\u003c/em\u003e. These might be paired with regionally appropriate non-floating species, e.g. \u003cem\u003eLessonia\u003c/em\u003e spp, \u003cem\u003eUndaria\u003c/em\u003e spp, \u003cem\u003eLaminaria\u003c/em\u003e spp and \u003cem\u003eSaccharina\u003c/em\u003e spp. There are also many types of configurations that could be used. In this research we used closely spaced lines, alternating species of each test species. Alternatively, in future work it may be possible to seed both species on the same line. Another major issue with the co-cultivation of two kelp species is finding the optimal method to grow the two species on one structure. \u003cem\u003eNereocystis\u003c/em\u003e is an ideal candidate from a biomass perspective, but it has proven problematic due to bleaching as it reaches the surface. Since other kelps such as \u003cem\u003eMacrocystis\u003c/em\u003e and \u003cem\u003eEualaria\u003c/em\u003e do not have that issue in Alaska, they might be better in a co-cultivation system.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the United States Department of Energy Advanced Research Projects Agency-Energy (ARPA-E) Macroalgae Research Inspiring Novel Energy Resources (MARINER) award #DE-AR0000911 to the University of Alaska Fairbanks.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFinancial interests: The authors declare they have no financial interests.\u003c/p\u003e\n\u003cp\u003eNon-financial interests: none.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and material\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOn publication data files will be available through ScholarWorks@UA (https://scholarworks.alaska.edu/), an open data repository. The datasets generated during and/or analyzed during the current study are also available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMS, SL, CY, LR, KB - Conceptualization\u003c/p\u003e\n\u003cp\u003eMS, DB, AP, LM, CG, HK, SL, LR, KB - Methodology\u003c/p\u003e\n\u003cp\u003eMS, DB - Formal analysis and investigation\u003c/p\u003e\n\u003cp\u003eMS, DB, AP, LM, CG, HK, SL, LR, KB, CY - Writing - original draft preparation and review and editing\u003c/p\u003e\n\u003cp\u003eMS, SL - Funding acquisition\u003c/p\u003e\n\u003cp\u003eLR, KB - Resources\u003c/p\u003e\n\u003cp\u003eMS - Supervision of Research, PI UAF\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe are grateful for the in-kind contributions by GreenWave and C.A. Goudey \u0026amp; Associates. \u0026nbsp;Logistic support was provided by the UAF Kodiak Seafood and Marine Science Center.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAugyte S, Yarish C, Redmond S, Kim JK (2017) Cultivation of a morphologically distinct strain of the sugar kelp, \u003cem\u003eSaccharina latissima\u003c/em\u003e forma angustissima, from coastal Maine, USA, with implications for ecosystem services. J Appl Phycol 29:1967\u0026ndash;1976. https://doi.org/10.1007/S10811-017-1102-X\u003c/li\u003e\n \u003cli\u003eBrayden C, Coleman S (2023) Maine Seaweed Benchmarking Report. Maine Aquaculture Association. https://maineaqua.org/wp-content/uploads/2023/08/Maine-Seaweed-Benchmarking-Report.pdf\u003c/li\u003e\n \u003cli\u003eFlavin N, Flavin K, Flahive B (2013) Kelp Farming Manual a Guide to the Processes, Techniques, and Equipment for Farming Kelp in New England Waters. Ocean Approved. https://www.researchgate.net/publication/311946411\u003c/li\u003e\n \u003cli\u003eForbord S, Matsson S, Brodahl GE, Bluhm BA, Broch OJ, Hand\u0026aring; A, Metaxas A, Skjermo J, Steinhovden KB, Olsen Y (2020) Latitudinal, seasonal and depth-dependent variation in growth, chemical composition and biofouling of cultivated \u003cem\u003eSaccharina latissima\u0026nbsp;\u003c/em\u003e(Phaeophyceae) along the Norwegian coast. J Appl Phycol 32:2215\u0026ndash;2232. https://doi.org/10.1007/s10811-020-02038-y\u003c/li\u003e\n \u003cli\u003eGruenthal K, Habicht C (2022) Literature review for implementation of the 50-50 rule for cultivation of seaweeds and other aquatic plants in Alaska. Report number: RIR.2A.2022.01, Alaska Department of Fish and Game.https://www.researchgate.net/publication/371534772; accessed 12April 2024.\u003c/li\u003e\n \u003cli\u003eGuillard RRL (1975) Culture of phytoplankton for feeding marine invertebrates. In: Smith WL, Chanley MH (Eds.) Culture of Marine Invertebrate Animals. Plenum Press, New York, USA. pp 26- 60.\u003c/li\u003e\n \u003cli\u003eHwang EK, Boo GH, Graf L, Yarish C, Yoon HS and Kim JK (2022) Kelps in Korea: from population structure to aquaculture to potential carbon sequestration. Algae 37:85-103. http://doi.org/10.4490/algae.2022.37.3.3.\u003c/li\u003e\n \u003cli\u003eJung JW, Pereira R, Yarish C, Kim JK (2024) Seaweed aquaculture: from cultivars to cultivation technologies to applications. In: Pereira R (ed) Aquaculture and living resource management, Volume 2. CRC Press (Taylor \u0026amp; Francis Group) Boca Raton. ISBN 978-1-032-34632-8.\u003c/li\u003e\n \u003cli\u003eKerrison PD, Stanley MS, Kelly M, MacLeod A, Black KD, Hughes AD (2016) Optimizing the settlement and hatchery culture of \u003cem\u003eSaccharina latissima\u003c/em\u003e (Phaeophyta) by manipulation of growth medium and substrate surface condition. J Appl Phycol 28:1181\u0026ndash;1191. https://doi.org/10.1007/S10811-015-0621-6\u003c/li\u003e\n \u003cli\u003eKim JK, Stekoll M, Yarish C (2019) Opportunities, challenges and future directions of open-water seaweed aquaculture in the United States. Phycologia, 58: 446-461. DOI: 10.1080/00318884.2019.1625611\u003c/li\u003e\n \u003cli\u003eKite-Powell HL, Ask E, Augyte S, Bailey D, Decker J, Goudey CA, Grebe G, Lic Y, Lindell S, Manganelli D, Marty-Rivera M, Ng C, Roberson L, Stekoll M, Umanzor S, Yarish C (2022) Estimating production cost for large-scale seaweed farms. Appl Phycol 3:435\u0026ndash;445. https://doi.org/10.1080/26388081.2022.2111271\u003c/li\u003e\n \u003cli\u003eLi Y, Umanzor S, Ng C, Huang M, Marty-Rivera M, Bailey D, Aydlett M, Jannink J-L, Lindell S, Yarish C(2022) Skinny kelp (\u003cem\u003eSaccharina angustissima\u003c/em\u003e) provides valuable genetics for the biomass improvement of farmed sugar kelp (\u003cem\u003eSaccharina latissima\u003c/em\u003e). J Appl Phycol 34:2551\u0026ndash;2563. https://doi.org/10.1007/s10811-022-02811-1\u003c/li\u003e\n \u003cli\u003eMerrill JE, Gillingham DM (1991) Bull Kelp Cultivation Handbook. National Coastal Resources Research and Development Institute, Portland.\u003c/li\u003e\n \u003cli\u003eRatcliff JJ, Soler-Vila A, Hanniffy D, Johnson MP, Edwards MD (2017). Optimisation of kelp (\u003cem\u003eLaminaria digitata\u003c/em\u003e) gametophyte growth and gametogenesis: effects of photoperiod and culture media. J Appl Phycol 29:1957\u0026ndash;1966. https://doi.org/10.1007/S10811-017-1070-1\u003c/li\u003e\n \u003cli\u003eRaymond AET, Stekoll MS (2021). Conditions for staggering and delaying outplantings of the kelps \u003cem\u003eSaccharina latissima\u003c/em\u003e and \u003cem\u003eAlaria marginata\u003c/em\u003e for mariculture. J World Aquacult Soc 52:1135\u0026ndash;1157. https://doi.org/10.1111/jwas.12846\u003c/li\u003e\n \u003cli\u003eRedmond S, Green L, Yarish C, Kim J, Neefus C (2014) New England seaweed culture handbook. \u003cem\u003eseaweed cultivation\u003c/em\u003e. Connecticut Sea Grant. https://opencommons.uconn.edu/seagrant_weedcult/1\u003c/li\u003e\n \u003cli\u003eSetthamongkol P, Tunkijjanukij S, Satapornvanit K, Salaenoi J (2015) Growth and nutrients analysis in marine macroalgae. Agriculture and Natural Resources 49:11\u0026ndash;218. https://li01.tci-thaijo.org/index.php/anres/article/view/243563\u003c/li\u003e\n \u003cli\u003eShea R, Chopin T (2007) Effects of germanium dioxide, an inhibitor of diatom growth, on the microscopic laboratory cultivation stage of the kelp,\u003cem\u003e\u0026nbsp;Laminaria saccharina\u003c/em\u003e. J Appl Phycol 19:27\u0026ndash;32. https://doi.org/10.1007/s10811-006-9107-x\u003c/li\u003e\n \u003cli\u003eStekoll MS, Deysher LE, Hess M (2006) A remote sensing approach to estimating harvestable kelp biomass. J Appl Phycol 18:323-334.\u003c/li\u003e\n \u003cli\u003eStekoll MS, Peeples TN, Raymond AET (2021) Mariculture research of \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e and \u003cem\u003eSaccharina latissima\u003c/em\u003e in southeast Alaska. J World Aquacult Soc 52:1031-1046. https://doi.org/10.1111/jwas.12765\u003c/li\u003e\n \u003cli\u003eStephens T, Heifetz L, Stanley M (2023) Farming bull kelp: lessons learned and future considerations. Barnacle Foods, Juneau. https://docs.google.com/document/d/1vR4tTuYMizg9QVRuMXcIja7LYE0IX1_cy-un8O2jCZo/edit#heading=h.yaxs6rms40hi); accessed 12 April 2024.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Macroalgae, aquaculture, bull kelp, sugar kelp, Nereocystis, Saccharina","lastPublishedDoi":"10.21203/rs.3.rs-4263270/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4263270/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eInterest in farming kelps has grown beyond using kelp for food, feed or biofuels. There is considerable interest in generating biomass from seaweed for use in bioplastics and other products that would substitute for petroleum-derived products. For these uses to be viable, large amounts of biomass are needed. Very large kelp farms can be expensive to build and maintain, leading to the need to optimize the biomass per unit area. Although close spacing of growlines can lead to poor growth, a viable approach may be to grow two species of kelps together: one that hangs down and one that is buoyant, growing up. This system would increase the spacing in three dimensions. In Alaska, \u003cem\u003eSaccharina latissima\u003c/em\u003e is commonly grown hanging down from longlines. One of the buoyant Alaskan kelps is \u003cem\u003eNereocystis luetkeana.\u003c/em\u003e Because there are commercial uses for wild-harvested \u003cem\u003eNereocystis\u003c/em\u003ein Alaska, we undertook a preliminary trial in Kodiak, Alaska that grew both \u003cem\u003eSaccharina\u003c/em\u003e and \u003cem\u003eNereocystis\u003c/em\u003e in the same longline array. Closely spaced lines were seeded the first week of February 2023 and set at 3m below the surface. The arrays were harvested in late June 2023. Total yields were greatest on the combined arrays, followed by the \u003cem\u003eNereocystis\u003c/em\u003eonly and \u003cem\u003eSaccharina\u003c/em\u003e only arrays. Despite having 45% fewer grow-lines, the total yield of the \u003cem\u003eNereocystis \u003c/em\u003eon the combined arrays was statistically similar to the \u003cem\u003eNereocystis\u003c/em\u003e only arrays. These results may have significance for large scale macroalgal production.\u003c/p\u003e","manuscriptTitle":"Optimizing Seaweed Biomass Production - A Two Kelp Solution","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-18 11:35:30","doi":"10.21203/rs.3.rs-4263270/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-05-10T02:00:45+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-10T01:11:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-09T03:37:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"19925a9d-8724-4745-8342-3ba197dec7e9","date":"2024-04-20T09:54:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"d6f212a4-3b6e-4edd-bfe3-d36b6141363d","date":"2024-04-18T06:10:27+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-16T05:51:22+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-16T05:48:02+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-16T04:36:34+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Applied Phycology","date":"2024-04-14T01:07:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f5e690cb-2dbc-46db-a73f-d40b416521fe","owner":[],"postedDate":"April 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-06-06T12:26:10+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-18 11:35:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4263270","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4263270","identity":"rs-4263270","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}