Impacts of microplastics and carbamazepine on the shell formation of thick-shell mussels and the underlying mechanisms of action

Forming calcareous exoskeletons is crucial for the health and survival of calcifiers such as bivalves. However, the impacts of waterborne emergent pollutants on this important process remain largely unknown. In this study, the effects of two types of emergent pollutants, microplastics (MPs) and carbamazepine (CBZ), which are ubiquitously present in ocean environments, on shell formation were assessed in the thick-shell mussel (Mytilus coruscus) with a shell regeneration experiment. In addition, their impacts on the in vivo contents of ATP, Ca, carbonic anhydrase (CA), and bone morphogenetic protein receptor type-2 (BMPR2), the activity of phosphofructokinase (PFK) and Ca-ATPase, and the expression of shell-formation related genes were analyzed. The data collected demonstrated that shell regeneration after mechanical injury was significantly arrested by CBZ and/or MPs. Besides, all the physiological and molecular parameters investigated were markedly suppressed by these two pollutants. Furthermore, synergistic impacts on most of the parameters examined were observed between CBZ and MPs. Our results indicate that these two pollutants may disrupt shell formation by constraining the availability of raw materials and energy, inhibiting the formation of the organic shell matrix, and interfering with the regulation of crystallization, which may have far-reaching impacts on the health of marine calcifiers.