Effects of hypercapnia on acid–base balance and osmo-/iono-regulation in prawns (Decapoda: Palaemonidae)

Anthropogenic carbon dioxide-induced 'ocean acidification' is predicted to have major implications for marine organisms.As the oceans becomes increasingly hypercapnic (elevated CO 2 ) and seawater pH decreases, the ability of organisms to maintain extracellular pH homeostasis (acidbase balance) may be compromised.Acid -base regulation occurs by ionic transport, where hydrogen and bicarbonate ions (HCO 3 -) are exchanged for sodium and chloride, respectively (H + /Na + ; HCO 3 -/Cl -), as exemplified by decapod crustaceans.Palaemonid prawns, in particular, are efficient hypo-ionic/osmotic regulators in seawater.We demonstrate that hypercapnic exposure (0.3 kPa) results in short-term (5 to 14 d) extracellular acidosis in 2 efficient ionic/osmo-regulators (thus, acid -base regulators), i.e.Palaemon elegans and P. serratus.Complete hypercapnic compensation was observed in both species after 30 d exposure with no effect on osmotic capacity, but at the expense of extracellular acid -base alteration (alkalosis).Furthermore, the predominantly subtidal species P. serratus was observed to be as tolerant as the intertidal species P. elegans, although 2 differing mechanisms of ionic regulation may be at work, with P. elegans and P. serratus displaying lower and elevated haemolymph ion concentrations (i.e.sodium, chloride and calcium), respectively.