Investigations were performed on variations of photosynthetic pigment in conchocelis of Alaskan Porphyra species, P. abbottae (Pa), P. pseudolanceolata (Pe), P. pseudolinearis (Pi) and P. torta (Pt), in response to environmental variables. Conchocelis were cultured under varying conditions of irradiance (0, 10, 40 and 160 µmol photons m-2s-1), nutrient concentration (0, f/4, f/2 and f) for up to 60 days (with temperature 11°C and salinity 30ppt). Chlorophyll a (Chl a ) content was measured by spectrophotometry. Results indicated that Chl content varied with different culture conditions and species. Photosynthetic pigment was significantly affected by irradiance, nutrient concentration and culture duration, including some interactions of major factors for different species. Light had the most obvious influence on pigment content. For all four species and culture conditions tested, the higher Chl a content (3.6-8.6 mg/g.dw) generally occurred at 0-10 µmol photons m 2 s 1than at higher irradiances (≥40 µmol photons m-2s-1 ) culture. For all culture conditions, Chl a content in conchocelis culture with no nutrients added was the lowest. Although there was some difference in Chl a content for cultures with f/2-f nutrient concentration, it was not statistically significant. ANOVA results showed that culture duration had influence on Chl a content of Pa, Pe and Pi species. However, pooled data analysis indicated there was no obvious difference in Chl content for four species of 10-60day culture. There were significant differences in photosynthetic pigment content for different species. Pa and Pi produced much higher pigment content than the other two species responding to different environmental conditions. Maximal Chl. a content (8.6 mg/g.dw) for Pa occurred at 0 µmol photons m-2s-1, f/2 nutrient concentration and 10 day culture duration. Pt contained the lowest pigment content for all culture conditions. Photosynthetic pigment remained relatively higher content under the complete darkness or the low irradiance continuously as long as 60 days for all tested species, which demonstrated the unique survival feature of Porphyra conchocelis. Variation patterns of pigment content, ecological significance and adaptation strategy to low or dark light conditions for microscopic conchocelis stage of Porphyra were discussed.

Does density affect recruitment and growth in the annual, blade phase of Pyropia sp., does self-thinning occur, and does substrate affect recruitment? These questions were investigated in laboratory-cultured Pyropia torta, a naturally occurring species in Alaska with mariculture potential. Three density levels were produced from conchospores. Measurements were made, initially at settlement and germination and, subsequently, at approximately 3-week intervals, in 12 randomly selected cultures from each density level. Settled spores, germlings, or growing blades were counted microscopically and standardized to unit area. Blade surface area was measured microscopically using image analysis software. Three density levels were still distinct at germination, but the high and medium levels were not significantly different. The germination rate of conchospores was highest at the medium density level, suggesting facilitation at moderate densities but inhibition at higher densities. Significant self-thinning occurred at each density level but differed among levels, while overall blade growth was about 10-fold greater at low density than at the other two levels. In a separate experiment, counts of attached spores per unit area on artificial substrate materials were greatest on materials with interstitial spaces large enough to trap spores until they become firmly attached.

On publication, data files will be available through ScholarWorks@UA (https://scholarworks.alaska.edu/handle/11122/15071), an open data repository. The datasets generated during the current study are also available from the corresponding author on reasonable request.

Seaweed farming has the potential to produce feedstocks for many applications, including food, feeds, fertilizers, biostimulants, and biofuels. Seaweeds have advantages over land-based biomass in that they require no freshwater inputs and no allocation of arable land. To date, seaweed farming has not been practiced at scales relevant to meaningful biofuel production. Here we describe a techno-economic model of large-scale seaweed farms and its application to the cultivation of the cool temperate species Saccharina latissima (sugar kelp) and the tropical seaweed Eucheumatopsis isiformis. At farm scales of 1000 ha or more, our model suggests that farm gate production costs in waters up to 200 km from the onshore support base are likely to range between $200 and $300 per dry tonne. The model also suggests that production costs below $100 per dry tonne may be achievable in some settings, which would make these seaweeds economically competitive with land-based biofuel feedstocks. While encouraging, these model results and some assumptions on which they are based require further field validation.

We describe a method for production of kelp using meiospore seeding creating flexibility for extended storage time prior to outplanting. One bottleneck to expansion of the kelp farming industry is the lack of flexibility in timing of seeded twine production, which is dependent on the fertility of wild sporophytes. We tested methods to slow gametophyte growth and reproduction of early life stages by manipulating temperature of the kelp Saccharina latissima. Reducing temperature from 12 C to 4 C reduced gametophyte size, sporophyte size, egg production, and sporophyte production and subsequently was the best candidate condition for storage experiments of seeded twine. Next, we examined how storage of Alaria marginata and S. latissima seeded twine at 4 C under differing nutrient concentrations affected the viability of sporelings after being moved into optimal growth conditions. Seeded twine storage at 4 C with no alteration to culturing media showed no negative effects in sporophyte density and sporophyte length for both species. This method for seeded twine storage, “cold banking,” allowed seeded twine storage for at least an additional 36 days compared to standard methods, with a total of 56 days spent in the hatchery providing opportunity for outplanting timing and staggering to enhance aquaculture efficiency.