Description: Mytilus edulis were cultured for 3 months under six different seawater pCO(2) levels ranging from 380 to 4000 mu atm. Specimen were taken from Kiel Fjord (Western Baltic Sea, Germany) which is a habitat with high and variable seawater pCO(2) and related shifts in carbonate system speciation (e. g., low pH and low CaCO3 saturation state). Hemolymph (HL) and extrapallial fluid (EPF) samples were analyzed for pH and total dissolved inorganic carbon (C-T) to calculate pCO(2) and [HCO3-]. A second experiment was conducted for 2 months with three different pCO(2) levels (380, 1400 and 4000 mu atm). Boron isotopes (delta B-11) were investigated by LA-MC-ICP-MS (Laser Ablation-Multicollector-Inductively Coupled Plasma-Mass Spectrometry) in shell portions precipitated during experimental treatment time. Additionally, elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF of specimen from the second experiment were measured via ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry). Extracellular pH was not significantly different in HL and EPF but systematically lower than ambient water pH. This is due to high extracellular pCO(2) values, a prerequisite for metabolic CO2 excretion. No accumulation of extracellular [HCO3-] was measured. Elemental ratios (B/Ca, Mg/Ca and Sr/Ca) in the EPF increased slightly with pH which is in accordance with increasing growth and calcification rates at higher seawater pH values. Boron isotope ratios were highly variable between different individuals but also within single shells. This corresponds to a high individual variability in fluid B/Ca ratios and may be due to high boron concentrations in the organic parts of the shell. The mean delta B-11 value shows no trend with pH but appears to represent internal pH (EPF) rather than ambient water pH.

Description: The present study provides a first finding of the acid-base regulating machinery (ion-transporters relevant for acid-base regulation) in cephalopod, and series of studies showed that they exhibit specialized ion regulatory cells (ionocytes) on their skin and yolk epithelium. A feature that was so far only reported for fish. In addition, several ion regulatory genes were identified in cephalopod to be involved in the compensation of CO2 induced acid-base disturbances, including Na+/H+-exchanger (NHE3), ammonium transporters (Rhcg) and vacuolar H+-ATPase (VHA) by being significantly up regulated in response to elevated sea water pCO2. Here we show for the first time that cephalopod embryos exhibit epidermal ionocytes and that the skin is a mayor site for proton excretion. Similar to fish, ionocytes located on the skin and yolk of cephalopod embryos are characterized by high concentrations of mitochondria. These similar responses towards elevated water pCO2 and sensitivity thresholds during life history may be explained by convergent acid-base regulatory features of cephalopods and fish.