Metabolic adaptations and reduced respiration of the copepod Calanoides carinatus during diapause at depth in the Angola-Benguela Front and northern Benguela upwelling regions

Abstract

Stage C5 copepodids and adult females of the herbivorous copepod Calanoides carinatus were sampled in the Angola-Benguela frontal region and northern Benguela upwelling area off Namibia in February–March 2002, using a multiple opening/closing net system. Respiration rates of C5s collected between 400m and 700m were measured onboard at the simulated in situ temperature of 8°C and at sea surface temperature (SST ≥20°C). These data were compared to the oxygen demand of epipelagic individuals of C. carinatus caught in the upper 30m and incubated at ambient SST. Deep-living C5s consumed 0.21 ± 0.08ml O₂ h⁻¹ (g dry mass)⁻¹ at 8°C and 0.96ml O₂ h⁻¹ (g dry mass)⁻¹ (range 0.84–1.09) at 25.9°C. These results were substantially lower than respiration rates of 5.23 ± 0.55ml O₂ h⁻¹ (g dry mass)⁻¹ in epipelagic individuals incubated at SST. The results reveal a reduction by 96% of metabolic rate in deep-living, diapausing C5s relative to surface-dwelling, active individuals. Only 14.4% of this metabolic reduction is explained by the lower ambient temperature at depth and a Q₁₀ value of 2.34. Therefore, the major fraction (81.6%) of the metabolic reduction is attributable to active physiological changes or processes during diapause at depth. The study emphasises the importance for herbivorous copepods, in areas with a highly variable food supply, to adopt a dormant phase in their life cycle in order to survive long periods of starvation.

Keywords:

• CALANOIDES CARINATUS
• COASTAL UPWELLING REGION
• COPEPOD
• DIAPAUSE
• LIFE CYCLE
• METABOLISM
• OXYGEN
• RESPIRATION
• SOUTH ATLANTIC