Water bicarbonate modulates the response of the shore crab Carcinus maenas to ocean acidification


Ocean acidification causes an accumulation of CO2 in marine organisms and leads to shifts in acid–base parameters. Acid–base regulation in gill breathers involves a net increase of internal bicarbonate levels through transmembrane ion exchange with the surrounding water. Successful maintenance of body fluid pH depends on the functional capacity of ion-exchange mechanisms and associated energy budget. For a detailed understanding of the dependence of acid–base regulation on water parameters, we investigated the physiological responses of the shore crab Carcinus maenas to 4 weeks of ocean acidification [OA, P(CO2)w = 1800 µatm], at variable water bicarbonate levels, paralleled by changes in water pH. Cardiovascular performance was determined together with extra-(pHe) and intracellular pH (pHi), oxygen consumption, haemolymph CO2 parameters, and ion composition. High water P(CO2) caused haemolymph P(CO2) to rise, but pHe and pHi remained constant due to increased haemolymph and cellular [HCO3]. This process was effective even under reduced seawater pH and bicarbonate concentrations. While extracellular cation concentrations increased throughout, anion levels remained constant or decreased. Despite similar levels of haemolymph pH and ion concentrations under OA, metabolic rates, and haemolymph flow were significantly depressed by 40 and 30%, respectively, when OA was combined with reduced seawater [HCO3] and pH. Our findings suggest an influence of water bicarbonate levels on metabolic rates as well as on correlations between blood flow and pHe. This previously unknown phenomenon should direct attention to pathways of acid–base regulation and their potential feedback on whole-animal energy demand, in relation with changing seawater carbonate parameters.

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α :

Solubility coefficient; level of significance






Analysis of variance



[B]T :

Total boron concentration


Beats per minute


Degree celsius

c :


Ca2+ :

Calcium ion

Cl :

Chloride ion

CO2 :

Carbon dioxide


Chemical shift


Fast low angle shot




Gamma-aminobutyric acid

H+ :

Hydrogen ion/proton



HCO3 :

Hydrogen carbonate/bicarbonate ion


Hydrochloric acid

K+ :

Potassium ion




Molar (mol/L)



m :


Mg2+ :

Magnesium ion





\(\dot {M}{{\text{O}}_2}\) :

Metabolic-/respiration rate


Magnetic resonance imaging

n :

Amount of substance; group size

Na+ :

Sodium ion

NH4 + :

Ammonium ion


Nuclear magnetic resonance

O2 :




P :

(Partial-)pressure; probability

P(CO2)e :

Partial pressure of CO2 in haemolymph

P(CO2)w :

Partial pressure of CO2 in seawater

Pi :

Inorganic phosphate


− log10[H+]

pHe :

Extracellular pH

pHi :

Intracellular pH

pHw :

Sea water pH (free scale)

pK a :

− log10 of dissociation constant in an acid–base equilibrium

\({\text{p}}{K_{\text{a}}}^{{\prime \prime \prime }}\) :

pKa under defined conditions




Practical salinity unit


Parts per million


Rapid acquisition with relaxation enhancement


Routine metabolic rate

S :

Seawater salinity


Strong ion difference


Standard metabolic rate

SO4 2− :

Sulfate ion



T :


t :


V :


w f :

Wet weight/fresh weight


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The authors thank Fredy Veliz Moraleda and Silvia Hardenberg for assistance in animal maintenance. We thank Dr. Franz-Josef Sartoris for expertise on ion chromatography, Timo Hirse for assistance with the GC and Rolf Wittig for post-processing the MR data. We would like to thank three anonymous reviewers for their helpful comments, improving the manuscript.


The study is a contribution to the PACES II research program (WP 1.6) of the Alfred Wegener Institute, funded by the Helmholtz Association.

Author information

BM, CB and HP conceived and designed the experiments, and wrote and drafted the manuscript. BM carried out the experiments, with help from CB on MR experiments. BM performed the statistical analyses. All authors approved the final version of the manuscript.

Correspondence to Christian Bock.

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Communicated by G. Heldmaier.

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Maus, B., Bock, C. & Pörtner, H. Water bicarbonate modulates the response of the shore crab Carcinus maenas to ocean acidification. J Comp Physiol B 188, 749–764 (2018) doi:10.1007/s00360-018-1162-5

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  • Crustacean
  • Bicarbonate
  • Cardiac MRI
  • In vivo 31P NMR spectroscopy
  • Extracellular pH marker
  • Cardiovascular system