The effects of elevated temperature and ocean acidification on the metabolic pathways of notothenioid fish

Abstract

Organisms inhabiting the sub-zero waters surrounding Antarctica display remarkably narrow tolerances for environmental change. This study assessed three closely related fish exposed to simultaneous changes in oceanic conditions to ascertain the impact additive stress has on their capacity to acclimate and whether or not these fish employ similar metabolic responses.

Antarctic emerald rockcod have the capacity to compensate for warming when uncoupled from CO2‐acidification

“…As predicted, several aspects of cardiorespiratory physiology including heart rate ( f H ), ventilation rate ( f V ), and metabolic rate () significantly increased with warming. Most noteworthy, juvenile Trematomus bernacchii demonstrated a degree of thermal compensation and temperature acclimation that was much quicker than observed in the adults under Ambient P CO 2 (Enzor et al., , ; Jayasundara et al., ; Sandersfeld et al., ). The addition of elevated P CO 2 , however, appeared to create an interacting additive effect on hyperventilation, and a potential synergistic effect on (i.e., lower capacity for temperature acclimation when exposed to elevated P CO 2 ).…”

“…Simulated models project that the duration of low pH events in winter may increase in McMurdo Sound, thus exposing marine organisms to deleterious levels of pH for longer periods (Kapsenberg, Kelley, Shaw, Martz, & Hofmann, ). There are numerous studies investigating the effects of high temperature on the physiology of adult Antarctic fishes (Beers & Jayasundara, ; Bilyk & DeVries, ; Egginton & Campbell, ; Peck, Morley, Richard, & Clark, ; Sandersfeld, Davison, Lamare, Knust, & Richter, ; Sandersfeld, Mark, & Knust, ; Seebacher, Davison, Lowe, & Franklin, ; Somero & Hochachka, ; Weinstein & Somero, ); however, there are considerably fewer studies focused on how Antarctic fishes may respond to elevated P CO 2 , and the effects of elevated P CO 2 and temperature concurrently, with the focus on adult fishes (Enzor, Hunter, & Place, ; Enzor & Place, ; Enzor, Zippay, & Place, ; Strobel, Graeve, Pörtner, & Mark, ; Strobel, Leo, Pörtner, & Mark, ; Strobel et al., ) and only one study on an early life stage (i.e., embryos, Flynn, Bjelde, Miller, & Todgham, ). Since sensitivity to environmental stressors can vary across ontogeny (Hamdoun & Epel, ; Pörtner & Peck, ), we cannot predict species vulnerability to ocean changes of elevated P CO 2 and temperature by only evaluating sensitivity to change in adults.…”

“…Studies assessing the physiological impacts of warming on Antarctic fishes in the Nototheniidae family have shown changes to cardiorespiratory and metabolic performance (Egginton & Campbell, ; Enzor et al., , ; Franklin, Davison, & Seebacher, ; Jayasundara, Healy, & Somero, ; Seebacher et al., ); however, the degree of vulnerability and acclimation capacity may be species‐specific (Egginton & Campbell, ; Franklin et al., ; Jayasundara et al., ; Robinson & Davison, ,b; Seebacher et al., ). For example, studies of the emerald rockcod, Trematomus bernacchii , a dominant benthic species by biomass in the Ross Sea (Vacchi, La Mesa, & Greco, ), have demonstrated impacts of warming across several levels of organization, including limitations in cardiac performance (Jayasundara et al., ), sustained elevated metabolic costs (Enzor et al., , ), aerobic to anaerobic fuel switching (Enzor et al., ; Jayasundara et al., ), mitochondria break temperatures (Weinstein & Somero, ), a twofold increase in brain oxygen (O 2 ) consumption (Somero & DeVries, ), and up to an 85% reduction in growth (Sandersfeld et al., ). In comparison, the bald notothen Pagothenia borchgrevinki has exhibited less sensitivity to warming, demonstrating partial compensation for increased metabolic rates (Enzor et al., , ) and a greater capacity to cope marked by modifications in cardiorespiratory and metabolic adjustments (Franklin et al., ; Robinson & Davison, ,b; Seebacher et al., ).…”

“…For example, studies of the emerald rockcod, Trematomus bernacchii , a dominant benthic species by biomass in the Ross Sea (Vacchi, La Mesa, & Greco, ), have demonstrated impacts of warming across several levels of organization, including limitations in cardiac performance (Jayasundara et al., ), sustained elevated metabolic costs (Enzor et al., , ), aerobic to anaerobic fuel switching (Enzor et al., ; Jayasundara et al., ), mitochondria break temperatures (Weinstein & Somero, ), a twofold increase in brain oxygen (O 2 ) consumption (Somero & DeVries, ), and up to an 85% reduction in growth (Sandersfeld et al., ). In comparison, the bald notothen Pagothenia borchgrevinki has exhibited less sensitivity to warming, demonstrating partial compensation for increased metabolic rates (Enzor et al., , ) and a greater capacity to cope marked by modifications in cardiorespiratory and metabolic adjustments (Franklin et al., ; Robinson & Davison, ,b; Seebacher et al., ). Differential responses to warming may be explained by varied ecological niches of these species.…”

“…Trematomus bernacchii are more benthic, ranging from shallow to deeper waters (50–400 m), compared to P. borchgrevinki that live just under the annual sea‐ice potentially exposing them to more environmental variability and influencing a greater capacity to acclimate (Eastman, ). Although notothen species have showed varying responses to warming alone, the simultaneous addition of elevated CO 2 (i.e., multiple stressor) elicited more similar physiological responses (Enzor et al., , ; Strobel et al., ; Strobel, Graeve, et al., ; Strobel, Leo, et al., ). When exposed to elevated P CO 2 concurrently with warming, both species ( T. bernacchii and P. borchgrevinki ) exhibited significant increases in metabolic rates (Enzor et al., ) and mRNA expression of genes involved in the cellular stress response (Huth & Place, ,b).…”