eDNA sequencing of water, plastic and tissue of Pacific giant clam (Tridacna maxima) in a mesocosm approach for the P3M project, 2023
This study aimed to evaluate the impact of incrementally increasing plastic concentrations on the bacterial compartment in marine environments. We reproduced simplified tropical ecosystems in 9 seawater mesocosms, then immersed different quantities of macroplastics from pearl farm (copolymers of PP and PE). We then monitored the bacterial communities in three compartments: the water column, the Tridacna maxima and the plastic biofilm to identify the threshold at which modifications in the bacterial compartment occur. The objective was to identify early markers among impacted bacteria, indicative of potential risks exceeding critical thresholds for marine microbial fauna. Despite finding no influence of plastic concentration on bacterial diversity, significant impacts were observed for bacterial assemblages based on time and sample type. Digging deeper, our analysis at the individual bacterial scale revealed that at the highest plastic concentration (5.46g/L), a positive correlation was observed for 29 bacterial genera. This suggests that certain bacterial genera thrive at extreme concentrations of plastic, leading to an overabundance of these specific bacteria referred to here as candidate ASVs. The overabundance of candidate ASVs in ours mesocosms could be attributed to imbalanced competition relationships between bacteria, favouring genera less sensitive to environmental pollutants. Some of these bacteria have known ecological functions, including plastic degradation and pathogenicity, aligning with prior studies warning of the dangers associated with macroplastics in water, potentially promoting the emergence of pathogenic families by serving as substrates and modifying microbial interactions.