Moderate temperature and water flow increase growth during the nursery phase of Asparagopsis armata

The red seaweed Asparagopsis armata is a target species for commercial cultivation. However, to facilitate nursery production, optimal cultivation methods for the early life stages of this species need to be developed. Therefore, this study examined the interactive effects of temperature (15 degrees C, 18 degrees C and 21 degrees C), irradiance (15 and 30 mu mol photons m- 2 s- 1) and photoperiod (12 h L:12 h D and 8 h L:16 h D), and nutrient concentration (F/8 and F/4) and water flow (0.6 L min -1) on the development and growth of juvenile gametophytes of A. armata across two controlled laboratory experiments. Temperature and water flow had the greatest effect on the length of gametophytes, which was highest at 18 degrees C and with water flow. Gametophytes developed rapidly and were consistently largest when exposed to a 12 h L:12 h D photoperiod and growth increased when individuals were maintained at 15 mu mol photons m- 2 s- 1 compared to 30 mu mol photons m- 2 s- 1 under a 12 h L:12 h D photoperiod. Nutrients did not limit growth at either concentration, although contamination increased with increasing nutrient concentration and irradiance. Water flow is highly recommended during nursery cultivation of A. armata as this resulted in almost double the overall biomass productivity compared to static treatments. This work identifies critical parameters for enhancing development and growth during the early life stages of A. armata and provides fundamental information to facilitate system-specific upscaling and enable larger scale nursery production.