Indoor cultivation protocols for Devaleraea mollis and Palmaria hecatensis from Alaska: effects of temperature, light, and nutrients

Species diversification is crucial for the long-term viability, competitiveness, and sustainability of the seaweed farming industry in the USA. This study investigated the independent effects of 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) on the specific growth rate (SGR) of the red algae Devaleraea mollis and Palmaria hecatensis from Alaska. Outputs were used to refine 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 medium. Results indicated that both enrichment approaches resulted in similar SGRs without compromising biomass quality or increasing production costs. Both species exhibited a difference in phenotypic expression in response to temperature, photoperiod and irradiance, providing evidence for species-specific physiological adaptation. 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.