Abstract
Abstract. This article describes a potentiometric ocean acidification simulation system which automatically regulates pH through the injection of 100% CO2 gas into temperature-controlled seawater. The system is ideally suited to long-term experimental studies of the effect of acidification on biological processes involving small-bodied (10–20 mm) calcifying or non-calcifying organisms. Using hobbyist-grade equipment, the system was constructed for approximately USD 1200 per treatment unit (tank, pH regulation apparatus, chiller, pump/filter unit). An overall tolerance of ±0.05 pHT units (SD) was achieved over 90 days in two acidified treatments (7.60 and 7.40) at 12 °C using glass electrodes calibrated with synthetic seawater buffers, thereby preventing liquid junction error. The performance of the system was validated through the independent calculation of pHT (12 °C) using dissolved inorganic carbon and total alkalinity data taken from discrete acidified seawater samples. The system was used to compare the shell growth of the marine gastropod Zeacumantus subcarinatus infected with the trematode parasite Maritrema novaezealandensis with that of uninfected snails at pH levels of 7.4, 7.6, and 8.1.
Highlights
The carbon dioxide (CO2) produced by human activity since 1850 has reduced average surface oceanic pH from approximately 8.2 to 8.1, while current CO2 emission projections predict that oceanic pH will reach 8.06–7.77 by 2100 and approximately 7.41 by 2300 (IPCC, 2014)
The global reduction of ocean pH has become known as ocean acidification (OA), the term refers to changes in the concentration of carbonic acid and bicarbonate and carbonate ions, in addition to increased hydrogen ion activity (Reactions R1–R4)
The altered chemical speciation of seawater caused by OA poses a variety of challenges to all marine species, e.g. the maintenance of intra- and extra-cellular acid–base homeostasis in a more acidic environment (Pörtner et al, 2004) or the synthesis and dissolution of calcium carbonate (CaCO3) structures in seawater undersaturated with regard to component ions (Weiner and Dove, 2003)
Summary
The carbon dioxide (CO2) produced by human activity since 1850 has reduced average surface oceanic pH from approximately 8.2 to 8.1, while current CO2 emission projections predict that oceanic pH will reach 8.06–7.77 by 2100 and approximately 7.41 by 2300 (IPCC, 2014). It is accepted that OA research must move beyond single-species experiments and begin investigating the effects of combined abiotic factors, such as pH and temperature (Boyd, 2011), and the potential effects of OA on biological interactions such as competition (Hoffman et al, 2012), predation (Dixon et al, 2010; Allan et al, 2013), and parasitism (MacLeod and Poulin, 2012). We suggest goal tolerances, i.e. the variability around target parameter values expressed as standard deviations, for the control of these parameters: temperature (±0.5 ◦C), salinity (±0.6), pH (±0.05), and AT (±10 μmol kg−1) We believe these tolerance values represent realistic and achievable goals for OA simulation systems, as they can be met with relatively inexpensive apparatus and cause minimal changes to calculated carbonate parameters (Table 3)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
