## 4 Discussion
### Setup of Electrical Stimulation Methods and Conditions  
This study is the first to apply electrical stimulation technology to marine microalgae and _Bacillariophyta_, making it crucial to evaluate whether the stimulation method and conditions are appropriately designed.  
In terms of the stimulation method, direct current (DC) stimulation is easier to implement than pulse stimulation. The results show that continuous stimulation leads to prolonged contact between electrodes and algal solution, causing the microalgae to attach to the electrodes and form biofilms, which can negatively affect microalgal growth. This may partly account for the observed initial increase and subsequent decrease in cell  
Figure 11: Radar analysis of the effect of short-term direct current (DC) stimulation (**a**), continuous DC stimulation (**b**) on the growth and nutrients of _N. clostarium f. minutissima_ and overlaying radar charts for the control group (CK), D-3 V, and C-0.5 V (**c**).  
density within the continuous stimulation group, as well as the significant differences noted between the C-0 V and D-0 V groups. To address this, shortening the duration of continuous stimulation and reducing electrode-algal solution contact time is recommended. In contrast, short-term DC stimulation offers energy-saving advantages, and this study has demonstrated that it significantly promotes microalgal growth. Under suitable short-term stimulation conditions, _Nitzschia closerium f. minutissima_ exhibited a more than 13% increase in cell density, nearly 40% increase in chlorophyll a content, and over 67.66% increase in lipid content. These findings are consistent with [PERSON] et al.'s study on _Haematococcus pluvialis_, where a 1 min DC stimulation increased cell density by 1.2 times and improved both astaxanthin and chlorophyll content [15]. This indicates that short-term DC stimulation can effectively promote growth and nutrient accumulation in both freshwater and marine microalgae, and adjusting the stimulation duration may further enhance the cost-effectiveness. Therefore, short-term DC stimulation shows significant potential for future applications and research. Additionally, [PERSON] et al. noted that periodic short-term stimulation yields better effects compared to single applications [15]. Thus, future research and industrial practices should explore the optimization of microalgal cultivation through periodic short-term stimulation.  
Regarding stimulation conditions, preliminary experiments in this study found that applying voltages above 10 V caused rapid aggregation and lysis of marine microalgae. Due to the higher salinity of seawater compared to freshwater, electrolysis reactions are more likely to occur under the influence of an electric field, negatively affecting microalgal growth. Therefore, this study applied mild voltages and short electrical durations to minimize electrolysis reactions, aiming to reduce any impact on the medium's chemical properties while maintaining currents below 20 mA. Under these conditions, the electrochemical changes caused by electrolysis in the microalgal culture medium were theoretically negligible [21]. Based on electrical experiments, observations of algal aggregation behavior, and CV-curve measurements, this study confirmed that the stimulation conditions did not significantly alter the medium's properties nor cause severe stress to the cells, proving that the settings were appropriate.  
However, [PERSON] et al. reported that cathodic currents led to cell lysis, while anodic currents promoted astaxanthin biosynthesis in _Haematococcus pluvialis_[29]. This suggests that future research should consider the different effects of cathodic and anodic currents, and further investigate their roles in microalgal growth and metabolite production.