Oxygen Consumption and Carbon Budget in Groundwater-Obligate and Surface-Dwelling Diacyclops Species (Crustacea Copepoda Cyclopoida) Under Temperature Variability

This study explores the metabolic response and carbon budget of two cyclopoid copepod species, Diacyclops belgicus Kiefer, 1936 (a stygobitic, groundwater-adapted species) and Diacyclops crassicaudis crassicaudis (Sars G.O., 1863) (a stygophilic, predominantly surface-associated species). We measured oxygen consumption rates (OCRs), carbon requirements (CRs), ingestion (I) rates, and egestion (E) rates at 14 °C and 17 °C, representing current and predicted future conditions in the collection habitats of the two species. Diacyclops belgicus displayed OCRs (28.15 and 18.32 µL O2/mg DW × h at 14 and 17 °C, respectively) and carbon budget (CR: 0.14 and 0.10 µg C/mg × d at 14 and 17 °C) lower than those of D. crassicaudis crassicaudis (OCR: 55.67 and 47.93 µL O2/mg DW × h at 14 and 17 °C; CR: 0.3 and 0.27 µg C/mg × d at 14 and 17 °C). However, D. belgicus exhibited metabolic rates and carbon requirements comparable to those of other epigean species, challenging the assumption that low metabolic rates are universal among stygobitic species. Temperature variations did not significantly affect the metabolic responses and carbon requirements of the two species, suggesting that they may cope with moderate temperature increases.