Differential acid–base regulation in various gills of the green crab Carcinus maenas: Effects of elevated environmental pCO2

Abstract

Euryhaline decapod crustaceans possess an efficient regulation apparatus located in the gill epithelia, providing a high adaptation potential to varying environmental abiotic conditions. Even though many studies focussed on the osmoregulatory capacity of the gills, acid–base regulatory mechanisms have obtained much less attention. In the present study, underlying principles and effects of elevated pCO2 on acid–base regulatory patterns were investigated in the green crab Carcinus maenas acclimated to diluted seawater. In gill perfusion experiments, all investigated gills 4–9 were observed to up-regulate the pH of the hemolymph by 0.1–0.2 units. Anterior gills, especially gill 4, were identified to be most efficient in the equivalent proton excretion rate. Ammonia excretion rates mirrored this pattern among gills, indicating a linkage between both processes. In specimen exposed to elevated pCO2 levels for at least 7days, mimicking a future ocean scenario as predicted until the year 2300, hemolymph K+ and ammonia concentrations were significantly elevated, and an increased ammonia excretion rate was observed. A detailed quantitative gene expression analysis revealed that upon elevated pCO2 exposure, mRNA levels of transcripts hypothesized to be involved in ammonia and acid–base regulation (Rhesus-like protein, membrane-bound carbonic anhydrase, Na+/K+-ATPase) were affected predominantly in the non-osmoregulating anterior gills.