Microalgae are essential in aquaculture hatcheries during the early life stages of many marine species due to their high nutritional content. Conventionally, microalgae are cultured indoors under controlled conditions, but these systems are expensive and energy intensive. In tropical countries such as Seychelles, where high solar irradiance and stable temperatures prevail, outdoor cultivation could be a sustainable alternative. This study assessed the feasibility of outdoor cultivation of two species, Tetraselmis spp. and Chaetoceros muelleri, by comparing growth under different light and temperature conditions.
A total of fifteen 10L carboys were used in a factorial design outdoors: shaded-cooled, shaded-uncooled, unshaded-cooled, and unshaded-uncooled. An indoor control was maintained under continuous illumination at 25°C. Temperature and light were monitored twice daily, and cell densities were recorded every other day for five days. Trials were conducted separately for each species.
In the Tetraselmis spp. trial, cooled treatments maintained stable conditions compared to uncooled setups, which fluctuated more widely and reached higher light levels. The indoor control consistently produced the highest algal density (159,000 cells/ml), while outdoor treatments showed no significant differences, with unshaded-cooled reaching a peak of 101,000 cells/ml. For C. muelleri, uncooled treatments reached extreme temperatures, up to 43.8°C, while unshaded conditions, especially unshaded-cooled, promoted the highest algal growth (1.39 million cells/ml), significantly outperforming shaded treatments.
In conclusion, outdoor cultivation in Seychelles is viable, especially for C. muelleri under unshaded and moderately cooled conditions. This approach offers a promising, cost-effective solution for small-scale hatcheries in tropical regions. Further research should examine seasonal variation and long-term sustainability.