Table 4.

Impacts of high pCO₂ on gene expression and acid-base homeostasis in marine invertebrate taxa. ‘Acid-base homeostasis genes’ is a broad term that encompasses any gene involved in proton (H⁺) and bicarbonate (HCO₃⁻) transport as defined independently in each study. Arrows denote the direction of the response. In instances with both arrows, this reflects either overall differential expression (genes being both up and down regulated), or conflicting results across studies. Dashes indicate a non-significant response. It should be noted that physiological and gene expression measurements for a particular species may be confined to separate independent studies

Acid-Base Homeostasis
Phylum	Species	Acid-base homeostasis genes in response to high pCO2	External pCO2 / response in high pCO2	HCO3− levels / response in high pCO2	Range of pCO2 tested (μatm)	Refs
Arthropoda	Hyas araneus	↑ or ↓	Y / ↑	Y / ↑	420–3300	[71]
	Carcinus maenas	–	Y / -	Y / -	40–440 Pa	[68, 69]
Chordata	Acanthochromis polyacanthus	–	Y / ↑	Y / ↑	414–1900	[88, 89, 132]
	Gadus morhua	↑ or ↓	N	Y / ↑	550–2200	[91, 92, 133]
	Oryzias latipes	↑	N	N	393–7081	[93]
	Pagothenia borchgrevinki	–	N	N	427–1053	[94]
	Trematomus bernacchii	↑	N	N	430–1000	[97]
Echinodermata	Strongylocentrotus purpuratus	↓ or -	Y / ↓ or -	N	380–9556	[81, 85, 110, 134]
	Amphiura filiformis	↓	Y / ↓ (pH)	Y / ↑	492–6399	[72]