Biological and Biochemical Responses of Daphnia magna to Boron, Calcium, and Magnesium Deficiencies

Despite the critical role of essential nutrients in maintaining overall health in freshwater organisms, the effects of nutritional deficiency remain largely unknown. This study investigated the biological and biochemical effects of single and combined deficiencies of boron (B), magnesium (Mg), and calcium (Ca), essential nutrients for physiological functions, in Daphnia magna. Biological responses included life-history parameters (survival, growth, and reproduction), while biochemical effects comprised catalase (CAT) and glutathione S-transferase (GST) activity, as markers of oxidative stress and detoxification, respectively. B deficiency conditions significantly affected survival, growth, reproduction, and CAT activity, while Mg-deficient conditions were associated with significantly reduced survival, long-term growth, reproduction, and CAT activity. Under Ca-deficient conditions, the most severe responses were observed, including reduced survival, growth, reproduction and increased GST activity. Combined B omission with Ca or Mg also produced pronounced adverse responses compared with the corresponding single-nutrient deficiency conditions. Fluorescence imaging revealed treatment-dependent differences in B-associated fluorescence, consistent with differences in B availability. Impaired life-history traits and elevated GST activity suggest cellular stress or activation of detoxification processes associated with reduced organismal performance. The findings demonstrate that nutrient deficiencies act as chronic stressors, highlighting the ecological importance of essential nutrient scarcity in freshwater ecosystems.