Physiological Responses of brown mussel perna perna (Linnaeus, 1758) towards ocean acidiification

Abstract- Ocean Acidification (OA) in combination with global climatic change can negatively impact the distribution, dynamics and biology of shell forming animals by the lowering of calcium carbonate saturation states. The purpose of this study is to provide information on how increasing acidity can affect calcification of marine organisms. Investigations under laboratory microcosm conditions were conducted with the spat stage of brown mussel, Pernaperna (Linnaeus, 1758), a commercially important bivalve resource of the south west coast of India. The animals were maintained in triplicate at varying pH conditions of 5, 5.5, 6, 6.5, 7, 7.5, 8, and 8.5 for a short term exposure of 30days. The pH level of 8.2 was kept as control. It was observed that the spat could not survive pH below 6 and showed lower survival rate at pH below 8. The mussel spat exhibited reduced calcification and growth rates under different pH treatment conditions outside the normal range. The highest average gain in length was observed in animals maintained as control (treatment 1) and in the case of those maintained at pH above eight. Similarly shell weights were much lower for the reduced pH (6.5) conditions compared to the values in the control (8.2). The biochemical changes such as total tissue protein and biomarker enzyme activitiesin response to lowered pH showed significant difference (P<0.05) from control group. In general, the total tissue protein of experimental animals decreased with decreasing pH.Similarly the biomarker enzyme activities such as those due to lipid peroxidation, catalase, glutathione s transferase and reduced glutathione also were higher at acidic conditions possibly indicating greater stress to the organism at lowered pH.Rate of calcification, sodium concentration as well as potassium concentration of the spat shells also showed significant variations when exposed to varying pH treatments. Values of these parameters were found to be more in the case of animals maintained close to the control pH.Histological investigations conducted for assessing the tissue level changes due to variation in pH revealed that there weredeviations in cellular details in animals exposed to lower pH conditions compared to control. To summarize, microcosm experiments conducted with brown mussels proved that ocean acidification can contribute to lower growth rates and reduced survival coupled with alterations in physiological functions and shell integrity of calcifiers when exposed to sub-optimal conditions. Ocean acidification will likely pose more serious threats to marine organisms in the coming decades and thus warrants more research attention.