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Fewer studies have assessed the outdoor cultivation of Spirulina maxima compared with S. platensis, although the protein content of S. maxima is higher than S. platensis. Spirulina growth medium requires an increased amount of NaHCO3, Na2CO3, and NaNO3, which increases the production cost. Therefore, the current study used a low-cost but high-efficiency biomass production medium (Medium M-19) after testing 33 different media. The medium depth of 25 cm (group A) was sub-divided into A1 (50% cover with a black curtain (PolyMax, 12 oz ultra-blackout), A2 (25% cover), and A3 (no cover). Similarly the medium depths of 30 and 35 cm were categorized as groups B (B1, B2, and B3) and C (C1, C2, and C3), respectively, and the effects of depth and surface light availability on growth and biomass production were assessed. The highest biomass production was 2.05 g L-1 in group A2, which was significantly higher (p < 0.05) than that in all other groups and sub-groups. Spirulina maxima died in B1 and C1 on the fifth day of culture. The biochemical composition of the biomass obtained from A2 cultures, including protein, carbohydrate, lipid, moisture, and ash, was 56.59%, 14.42%, 0.94%, 5.03%, and 23.02%, respectively. Therefore, S. maxima could be grown outdoors with the highest efficiency in urea-enriched medium at a 25-cm medium depth with 25% surface cover or uncovered.

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Ocean warming and acidification can induce oxidative stress in marine species, resulting in cellular damage and apoptosis. However, the effects of pH and water temperature conditions on oxidative stress and apoptosis in disk abalone are poorly understood. This study investigated, for the first time, the effects of different water temperatures (15, 20, and 25 °C) and pH levels (7.5 and 8.1) on oxidative stress and apoptosis in disk abalone by estimating levels of H2O2, malondialdehyde (MDA), dismutase (SOD), catalase (CAT), and the apoptosis-related gene caspase-3. We also visually confirmed apoptotic effects of different water temperatures and pH levels via in situ hybridization and terminal deoxynucleotidyl transferase dUTP nick end labeling assays. The levels of H2O2, MDA, SOD, CAT, and caspase-3 increased under low/high water temperature and/or low pH conditions. Expression of the genes was high under high temperature and low pH conditions. Additionally, the apoptotic rate was high under high temperatures and low pH conditions. These results indicate that changes in water temperature and pH conditions individually and in combination trigger oxidative stress in abalone, which can induce cell death. Specifically, high temperatures induce apoptosis by increasing the expression of the apoptosis-related gene caspase-3.

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