Stephanie Maresseaa, Masayuki Tatsumia, b, David S Nicholsc, Rocky de Nysb,d, Jeffery T Wrighta
a Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Tasmania 7004, Australia.
b Sea Forest Ltd,488 Freestone Point Road, Triabunna, TAS 7190, Australia
c Central Sciences Laboratory, Division of Research, University of Tasmania, Hobart, TAS 7005, Australia
d James Cook University, College of Science and Engineering, Townsville, QLD, 4811, Austral
The red alga Asparagopsis armata produces secondary metabolites (bromoform) that, when fed in small amounts to cattle and sheep, reduce enteric methane emissions by up to 98%, and thus, present an opportunity for mass cultivation of natural bromoforms. This study aimed to determine the optimal abiotic conditions for cultivation through three experiments 1) the interactive effects of light and initial biomass, 2) the interactive effects of nutrients, light and temperature, and 3) the effect of different degrees of fragmentation on growth of A.armata and contaminant algae, and the concentration and net production of bromoforms. Light strongly increased biomass and bromoform production in A. armata averaging 1.9 g FW/l/week-1 and 44.9 mg/l/week-1 for biomass and bromoform production, respectively. Algae growth was further enhanced by the combined effects high light and high nutrient conditions, however growth of the small brown algae Hincksia sandriania was also very high under those conditions (up to 50-60%). Contamination was lowest in low light (30-50 µmol photons m-1 s-1) and low nutrients (F10) treatments, although growth and bromoform production was also lower in those conditions (0.7-1.8 g/l/week-1 and 9.9-39.1 mg DW/l/week-1, respectively). Fragmenting tetrasporophytes increased biomass and bromoform production. Notably, tetrasporophytes that were cut 8- or 16-times had ~ 1.6 times the biomass and 3-3.5 times the bromoform production compared to tetrasporophytes cut zero times. Overall, these results suggest light, and fragmentation can be manipulated to upscale growth and bromoform production, hereby providing a strong foundation to develop an industry protocol to cultivation of A.armata tetrasporophytes.