## 3 Results and Discussion
### Physiological Effects on Cyclotella meneghiniana  
The generation of fucoxanthin in macroalgae ranges from 0.001 to 0.356% DW, with microalgae yielding more advantageous amounts of fucoxanthin than macroalgae [56; 57]. The output of fucoxanthin depends on the type of microalgae, its growth, the content of fucoxanthin, and the efficiency of extraction [6]. The autotrophic growth of microalgae is facilitated by photosynthesis, enriched with light, inorganic nutrients, and carbon dioxide inorganic nutrients present in the water [58]. The proliferation of algae is shaped by a mix of physical, chemical, and biological elements, predominantly light and nutrients [59]. Our research focused on examining microalgae biomass at three different light levels, revealing that _Cyclotella meneghiniana_ in low-light conditions exhibited the greatest cell density after a 12-day incubation period (Figure 4a). The outcome mirrors that of _Cyclotella cryptic_ CCMP333, where a minimal light intensity of 30 umol photons m\({}^{-2}\) s\({}^{-1}\) was employed to achieve the peak biomass concentration (roughly 1.25 g L\({}^{-1}\)) [47]. One plausible reason for this occurrence could be the prolonged acclimatization of experimental microalgae to certain culture environments prior to conducting experiments with varying light intensities. Nutrients such as nitrogen and phosphorus play a fundamental role in the growth of phytoplankton [60]. Typically, the proliferation of microalgae is constrained by the levels and respective ratios of nitrate (N) and phosphorus (P) present in the aquatic environment [58]. We adjusted different nutrient condition variables under low-light conditions to compare with the control group (F/2 group) and found that the HN (Figure 4b) and MP (Figure 4c) groups had significantly higher biomass than the other groups. In general, diatoms are the dominant species in phytoplankton cultures with high nitrogen to phosphorus ratios [61]. This is similar to the findings that nitrate enrichment alone promoted algal growth [62]. Another study was similar to the conclusion of this paper that the biomass of diatoms increased with the increase in the nitrogen concentration when cultured under nitrogen-rich conditions [63]. Interestingly, medium concentrations of phosphorus (MP) in this experiment would promote diatom biomass production more than low (C) or high (HP) phosphorus concentrations (Figure 4c). Our single change  
Figure 3: Phylogram constructed using ITS1 sequences of _Cyclotella meneghiniana_ (_Stephanocyclulus meneghinianus_). Phylogram was constructed by the neighbor-joining method using the K2P distance protocol in MEGA ver.5.0. Numerical values at the nodes of the branches indicate bootstrap values and asterisks indicate species studied in this study. in the phosphorus concentration affected the nitrogen-phosphorus ratio in the medium, which may have been the key reason for affecting the algal cell growth. It is shown that a moderate phosphorus concentration favors algal growth, while too much phosphorus may alter the effect on the algal cell biomass due to changes in the nitrogen-phosphorus ratio. Similar studies have shown that the highest concentration of nitrogen and phosphorus (40 mg L\({}^{-1}\) NO\({}_{3}\) + 20 mg L\({}^{-1}\) PO\({}_{4}\)) did not have the greatest growth-promoting effect on _Ulva rigida_, while the appropriate concentration of nitrogen and phosphorus (30 mg L\({}^{-1}\) NO\({}_{3}\) + 15 mg L\({}^{-1}\) PO\({}_{4}\)) was more suitable for the growth of _Ulva rigida_[64]. The biomass of the HM group (Figure 4e) exhibited a notable increase compared to the control group, reaching (6.94 \(\pm\) 0.21) \(\times\) 10\({}^{6}\) cells mL\({}^{-1}\) following a period of growth lasting 12 days. Conversely, the cells within the LC group (Figure 4f) experienced a notable reduction in growth, recording a biomass of (3.70 \(\pm\) 0.23) \(\times\) 10\({}^{6}\) cells mL\({}^{-1}\) on the 12 th day.