Identifying the thermal optima for physiological performance and bromoform production of the red alga Asparagopsis taxiformis

Abstract The red alga Asparagopsis taxiformis has potential for methane mitigation in ruminant animals due to its high concentration of halogenated methane analogs. However, large scale production of A. taxiformis is constrained by intensive cultivation requirements. Additionally, the broad geographic distribution and several genetically distinct lineages of this seaweed require that cultivation strategies be tailored to a particular region. To address these limitations, we conducted two sequential experiments to investigate the thermal optima of a Lineage 2 strain of A. taxiformis . In the first experiment, cultures from Santa Catalina Island (Channel Islands, CA, USA) and La Jolla (San Diego, CA, USA) were exposed to temperatures from 13-30 °C to compare physiological responses (growth rates, maximum quantum yield of photosystem II (PSII), and bromoform production) across geographic locations. No significant differences between locations were observed, leading us to conduct a second experiment to test whether pre-acclimation to environmental variability improved thermal tolerance, comparing indoors versus outdoor cultivated cultures across an expanded temperature range of 8-33 °C. The outdoor strain of A. taxiformis was able to survive across a wide thermal range, with the highest growth rates, PSII photosynthetic yields, and bromoform concentrations observed at 23 °C. Previous exposure to environmental variability showed potential for acclimatation to elevated temperatures, with biomass increasing by 11% per day, accompanied by bromoform concentrations reaching roughly 3% of total dry weight (30 mg g −1 ). These findings provide critical insight into optimizing culture conditions and advancing the commercialization of A. taxiformis as a methane mitigation strategy in ruminants.