Cultivation protocols for the rhodophytes, Devaleraea mollis and Palmaria hecatensis from Alaska

Species diversification is crucial for the long-term viability, competitiveness, and sustainability of the seaweed farming industry in the United States. This study investigated the effects that temperature (4, 8 and 12°C), photoperiod (8L:16D, 12L:12D and 16L:8D), and irradiance (20, 40, 100 ± 10 µmol photons m ⁻² s ⁻¹ ) had on the specific growth rate (SGR) of Devaleraea mollis and Palmaria hecatensis from Alaska. Outputs were used to adjust indoor cultivation protocols for D. mollis and develop the first protocols for P. hecatensis . This study also explored the use of two low-cost commercial nutrient products (F/2 and Jack’s Special 25-5-15) as alternatives to the recommended nutrient medium, von Stosch Enrichment. Assessments determined whether their use resulted in similar SGRs without compromising biomass quality or raising production costs. Results showed that both species responded differently to each factor, indicating distinct ecological and physiological adaptations. D. mollis exhibited higher growth rates in warmer temperatures and responded to higher irradiance levels with spore release but showed no clear preference between neutral and long-day photoperiods. In contrast, P. hecatensis demonstrated higher growth rates in cooler environments with a long-day photoperiod promoting the most growth without spore release. Nutrient supplementation revealed that growth in D. mollis was affected by nutrient formulation, while P. hecatensis showed no significant growth variation. These findings underscore the importance of species and geographic-specific protocols for seaweed farming. Further research is needed to optimize the potential cultivation protocols provided here. Cultivation protocols would also benefit from exploring the ecological and physiological nuances of both species.