title: Effects of ocean acidification increase embryonic sensitivity to thermal extremes in Atlantic cod, Gadus morhua.
abstract: Thermal tolerance windows serve as a powerful tool for estimating the vulnerability of marine species and their life stages to increasing temperature means and extremes. However, it remains uncertain to which extent additional drivers, such as ocean acidification, modify organismal responses to temperature. This study investigated the effects of CO2-driven ocean acidification on embryonic thermal sensitivity and performance in Atlantic cod, Gadus morhua, from the Kattegat. Fertilized eggs were exposed to factorial combinations of two PCO2conditions (400 μatm vs. 1100 μatm) and five temperature treatments (0, 3, 6, 9 and 12 °C), which allow identifying both lower and upper thermal tolerance thresholds. We quantified hatching success, oxygen consumption (MO2) and mitochondrial functioning of embryos as well as larval morphometrics at hatch and the abundance of acid-base-relevant ionocytes on the yolk sac epithelium of newly hatched larvae. Hatching success was high under ambient spawning conditions (3-6 °C), but decreased towards both cold and warm temperature extremes. Elevated PCO2caused a significant decrease in hatching success, particularly at cold (3 and 0 °C) and warm (12 °C) temperatures. Warming imposed limitations to MO2and mitochondrial capacities. Elevated PCO2stimulated MO2at cold and intermediate temperatures, but exacerbated warming-induced constraints on MO2, indicating a synergistic interaction with temperature. Mitochondrial functioning was not affected by PCO2. Increased MO2in response to elevated PCO2was paralleled by reduced larval size at hatch. Finally, ionocyte abundance decreased with increasing temperature, but did not differ between PCO2treatments. Our results demonstrate increased thermal sensitivity of cod embryos under future PCO2conditions and suggest that acclimation to elevated PCO2requires reallocation of limited resources at the expense of embryonic growth. We conclude that ocean acidification constrains the thermal performance window of embryos, which has important implication for the susceptibility of cod to projected climate change.
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany.|University of Bremen, NW 2 Loebener Str., 28359, Bremen, Germany.
authors.forename: Flemming T
authors.initials: FT
authors.lastname: Dahlke
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany.|University of Bremen, NW 2 Loebener Str., 28359, Bremen, Germany.
authors.forename: Elettra
authors.initials: E
authors.lastname: Leo
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany.
authors.forename: Felix C
authors.initials: FC
authors.lastname: Mark
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany.|University of Bremen, NW 2 Loebener Str., 28359, Bremen, Germany.
authors.forename: Hans-Otto
authors.initials: HO
authors.lastname: Pörtner
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Bickmeyer
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany.|Hochschule Bremerhaven, An der Karlstadt 8, 27568, Bremerhaven, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Frickenhaus
authors.affiliation: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570, Bremerhaven, Germany.
authors.forename: Daniela
authors.initials: D
authors.lastname: Storch
mesh_terms: D000064:Acclimatization; D000818:Animals; D057231:Climate Change; D048389:Gadus morhua; D006863:Hydrogen-Ion Concentration; D009792:Oceans and Seas; D013696:Temperature
keywords: Atlantic cod; aerobic metabolism; embryonic development; hatching success; mitochondrial respiration; ocean acidification; ocean warming; thermal tolerance window