Long-term impacts of ocean acidification on the Mediterranean mussel Mytilus galloprovincialis

This study aims to elucidate the long-term physiological impacts of ocean acidification on a key seafood species. The Mediterranean mussel Mytilus galloprovincialis, was subjected to three pH conditions over a period of six months: two pH values within the present range of natural variability (pH_T: 8.10 and 7.80) and a lower pH condition (pH_T: 7.50) relevant in the context of near-future ocean acidification. A comprehensive assessment was conducted at the conclusion of the fourth and sixth months and encompassed a suite of physiological endpoints, including mortality, oxygen consumption, clearance rate, total haemocyte count (THC), nutritional content analysis, and polonium-210 (²¹⁰Po) depuration rates. The findings revealed a marked decrease in survival rates at pH 7.50 compared with those at pH 8.10 and 7.80 after six months of exposure. This was associated with a significant increase in THC and a decrease in lipid content. No significant pH effects were observed for other endpoints (namely clearance rate, condition index, oxygen consumption rate, protein and carbohydrate contents, and ²¹⁰Po). While the lack of response to low pH at some of these physiological endpoints may be a consequence of a lack of statistical power, our data clearly demonstrate the effects of low pH on the survival, THC, and lipid content of M. galloprovincialis. Such effects on a species' overall fitness have the potential to negatively impact this key seafood species, associated ecosystems, and the socioeconomic dynamics of communities depending on this resource.