Proteomic and Transcriptomic Responses Enable Clams to Correct the pH of Calcifying Fluids and Sustain Biomineralization in Acidified Environments

• Published in: International Journal of Molecular Sciences
• Main Authors: Caroline Schwaner, Sarah Farhat, John Haley, Emmanuelle Pales Espinosa, Bassem Allam
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: extrapallial fluid; hemolymph; hemocytes; clams; ocean acidification; biomineralization; Biology (General); QH301-705.5; Chemistry; QD1-999; Ocean acidification
• Online Access: https://doi.org/10.3390/ijms232416066; https://doaj.org/article/648fd33090da43408f694aebba684d39

Seawater pH and carbonate saturation are predicted to decrease dramatically by the end of the century. This process, designated ocean acidification (OA), threatens economically and ecologically important marine calcifiers, including the northern quahog ( Mercenaria mercenaria ). While many studies have demonstrated the adverse impacts of OA on bivalves, much less is known about mechanisms of resilience and adaptive strategies. Here, we examined clam responses to OA by evaluating cellular (hemocyte activities) and molecular (high-throughput proteomics, RNASeq) changes in hemolymph and extrapallial fluid (EPF—the site of biomineralization located between the mantle and the shell) in M. mercenaria continuously exposed to acidified (pH ~7.3; p CO 2 ~2700 ppm) and normal conditions (pH ~8.1; p CO 2 ~600 ppm) for one year. The extracellular pH of EPF and hemolymph (~7.5) was significantly higher than that of the external acidified seawater (~7.3). Under OA conditions, granulocytes (a sub-population of hemocytes important for biomineralization) were able to increase intracellular pH (by 54% in EPF and 79% in hemolymph) and calcium content (by 56% in hemolymph). The increased pH of EPF and hemolymph from clams exposed to high p CO 2 was associated with the overexpression of genes (at both the mRNA and protein levels) related to biomineralization, acid–base balance, and calcium homeostasis, suggesting that clams can use corrective mechanisms to mitigate the negative impact of OA.