Fine-scale variation in light climate can strongly regulate the reproductive, feeding, and bioenergetic performance of planktonic copepods, yet the combined and cross-generational effects of spectral composition, photoperiod, and irradiance remain poorly resolved. Here, we used an L₁₆(4³) orthogonal design to evaluate how contrasting light regimes regulate reproductive performance, feeding activity, bioenergetic balance, and fatty-acid composition in the marine copepod Dioithona rigida. Responses were compared between the acute-exposure F₁ generation and the multigenerationally acclimated F₄ generation to assess whether persistent light conditions reshape population-level stability and nutritional traits across generations. The F₄ generation showed higher reproductive output, increased female proportions, and lower trait variability than F₁, indicating enhanced population stability after sustained exposure to structured light regimes. Among the three factors, spectral composition exerted the strongest regulatory effect: blue light generally promoted reproduction, population increase, ingestion, net energy gain, and eicosapentaenoic acid (EPA) accumulation. Photoperiod produced trait-specific responses, suggesting a decoupling between foraging performance and lipid retention. A 12L:12D cycle favored reproductive stability and feeding, whereas longer photoperiods enhanced total fatty acids and essential fatty acids. Light intensity had weaker overall effects, although 1000-1400 lux generally supported better maternal performance. These results demonstrate that temporally and spectrally structured light regimes can generate distinct cross-generational responses in a planktonic copepod, linking environmental light variability with population maintenance, energy allocation, and nutritional quality formation. Blue light combined with 12L:12D to 18L:6D and 1000-1400 lux is recommended for stable population maintenance, while extended photoperiods under high irradiance may be used for targeted nutritional fortification.
 

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