Early hatchery protocols for tetrasporogenesis of the antimethanogenic seaweed Asparagopsis armata

Abstract

The red alga Asparagopsis armata is an emerging aquaculture-target species due to its application as an antimethanogenic feed ingredient in ruminants, yet information on A. armata reproduction and cultivation is currently lacking. We therefore quantified the effects of temperature, irradiance, nutrients, and photoperiod, and addition of plant growth regulators (PGRs; indole-3-acetic acid, abscisic acid, 1-aminocyclopropane-1-carboxylic acid) on tetrasporogenesis in domesticated A. armata that had been maintained under controlled conditions (18 °C, 12 h light:12 h dark photoperiod) for 18 months prior to experimentation. Tetrasporogenesis was only induced at 5 and 15 µmol photons m−2 s−1 under an 8 h light:16 h dark photoperiod with 3.5 mg nitrogen L−1 and tetraspore release was 28-fold greater at 18 °C compared to 15 °C after 28 days of exposure. After 29 days, tetraspore release and germination rate both declined. All PGR treatments prevented tetrasporogenesis. This study is the first to provide the detail and framework necessary to enable A. armata hatchery development. We conclude that tetrasporogenesis was most likely induced in response to a significant reduction in photoperiod rather than as a result of replicating seasonal environmental conditions, and that temperature played a key role in determining reproductive output. With overall higher tetraspore release and a consistent germination rate of > 90%, we recommend exposing tetrasporophyte biomass to 18 °C, 15 µmol photons m−2 s−1 and 3.5 mg nitrogen L−1 under an 8 h L:16 h D photoperiod for up to 29 days to obtain a reliable supply of tetraspores for seeding onto ropes for transfer to the hatchery phase.