The Black Sea, which is potentially the largest sink of CO₂ among the seas of the Atlantic Ocean, has been experiencing a decrease in pH over the last decades. Information on the acidification of the Black Sea and its impact on the marine biosystem is scarce. Based on literature and our own experimental data, we analyse the effect of low seawater pH values on the energy metabolism of the main commercial bivalve molluscs - the mussel Mytilus galloprovincialis and the oyster Magallana gigas. These species showed the ability to adapt energy metabolism levels over a wide pH range, from 7.0 to 8.1. When the pH was lowered by 0.1 unit, the oxygen consumption of mussels decreased on average by 10-20% in the pH range 7.5-8.2. At pH 7.2-7.5, the respiration rate of M. galloprovincialis did not change and remained at 9.15-9.38 μg O₂/(g dry tissue·h) and then dropped to 6.8 μg O₂/(g dry tissue·h) at pH 7.0. In M. gigas, the oxygen consumption rate decreased uniformly: on average by 10-15% for each 0.1 unit of pH change, up to pH value of 7.2. At pH 7.0-7.2, aerobic respiration of oysters was recorded at a minimum level of 4.6-4.8 μg O₂/(g dry tissue·h).
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