Publication Date:
2019-07-16
Description:
Introduction: Ongoing ocean warming and acidification increasingly affect marine ecosystems, in particular around
the Antarctic Peninsula. Yet little is known about the capability of Antarctic notothenioid fish to cope with rising
temperature in acidifying seawater. While the whole animal level is expected to be more sensitive towards
hypercapnia and temperature, the basis of thermal tolerance is set at the cellular level, with a putative key role for
mitochondria. This study therefore investigates the physiological responses of the Antarctic Notothenia rossii after
long-term acclimation to increased temperatures (7°C) and elevated PCO2 (0.2 kPa CO2) at different levels of
physiological organisation.
Results: For an integrated picture, we analysed the acclimation capacities of N. rossii by measuring routine
metabolic rate (RMR), mitochondrial capacities (state III respiration) as well as intra- and extracellular acid–base
status during acute thermal challenges and after long-term acclimation to changing temperature and hypercapnia.
RMR was partially compensated during warm- acclimation (decreased below the rate observed after acute
warming), while elevated PCO2 had no effect on cold or warm acclimated RMR. Mitochondrial state III respiration
was unaffected by temperature acclimation but depressed in cold and warm hypercapnia-acclimated fish. In both
cold- and warm-exposed N. rossii, hypercapnia acclimation resulted in a shift of extracellular pH (pHe) towards more
alkaline values. A similar overcompensation was visible in muscle intracellular pH (pHi). pHi in liver displayed a slight
acidosis after warm normo- or hypercapnia acclimation, nevertheless, long-term exposure to higher PCO2 was
compensated for by intracellular bicarbonate accumulation.
Conclusion: The partial warm compensation in whole animal metabolic rate indicates beginning limitations in
tissue oxygen supply after warm-acclimation of N. rossii. Compensatory mechanisms of the reduced mitochondrial
capacities under chronic hypercapnia may include a new metabolic equilibrium to meet the elevated energy
demand for acid–base regulation. New set points of acid–base regulation under hypercapnia, visible at the systemic
and intracellular level, indicate that N. rossii can at least in part acclimate to ocean warming and acidification. It
remains open whether the reduced capacities of mitochondrial energy metabolism are adaptive or would impair
population fitness over longer timescales under chronically elevated temperature and PCO2.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
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