Intraspecific differences in the metabolic response of amphipods to elevated CO2 and hypoxia

Abstract

Periodic episodes of low oxygen (hypoxia) and elevated CO2 (hypercapnia) accompanied by low pH occur naturally in Norwegian fjord systems. Under the influence of climate change, the geographic range and intensity of hypoxia and hypercapnia are predicted to increase, especially considering the phenomenon of Arctic amplification. To examine the metabolic variability and physiological capabilities of amphipods to these stressors, a series of physiological measurements were performed on latitudinal subpopulations (60° and 69°) of the amphipod Echinogammarus marinus, acclimated to different natural thermal regimes. The effects of elevated pCO2 and hypoxia, separate and together, on thermal sensitivity (Q10), metabolic rate, activation energy (Ea), aerobic threshold and aerobic scope were evaluated by determining whole-animal rates of oxygen uptake (MO2). Our results showed no metabolic cold adaptation in the colder-water, high-latitude population (69°). While MO2, aerobic threshold and scope were reduced compared to the more temperate population (60°), there was no difference in resting metabolic rate. After acclimatisation to a common temperature, the populations at 60° showed significantly greater metabolic flexibility by upregulating nearly all measured parameters. The effect of hypoxia, hypercapnia, and their combined effect significantly reduced the MO2, Q10, Ea, aerobic threshold and aerobic scope of the 60° population. At the same time, no changes were observed in the high-latitude population. However, mortality within this population when exposed to the stressors, separately and combined, increased. Amphipods near the northern limit of their distribution show different metabolic responses, with increased sensitivity to elevated pCO2 and hypoxia, than those in the south. Living on the edge of their thermal tolerance range, the scope of these populations to adapt their metabolic activities to compensate for the influence of environmental stressors is severely limited. Considering the phenomenon of Arctic amplification of climate change impacts, these populations are under considerable threat.