Marine fish intestine responds to ocean acidification producing more carbonate aggregates

Marine fish contribute to the carbon cycle by producing mineralized intestinal aggregates generated as by-products of their osmoregulation. Here we aimed at characterizing the control of intestinal aggregate production in the gilthead sea bream in response to near future increases of environmental CO2. Our results demonstrate that hypercapnia (800 and 1200 μatm CO2) elicits higher intestine epithelial HCO3−secretion and the subsequent parallel increase of intestinal aggregate production when compared to present values (400 μatm CO2). Intestinal gene expression analysis revealed the up-regulation of crucial transport mechanisms involved not only in the intestinal secretion cascade (Slc4a4, Slc26a3 and Slc26a6) of sea bream, but also in other mechanisms involved in intestinal ion uptake linked to water absorption such asNKCC2and theAquaporin 1b.These results highlight the important role of fish in the marine carbon cycle, and their potential growing impact of intestinal biomineralization processes in the scenario of ocean acidification.