Plastic-associated harmful phytoplankton assemblages in coastal and off-shore habitats of the Mediterranean Sea

Plastics (macro, micro and nanoplastics) are durable and persistent pollutants that may alter pelagic and coastal ecosystem functions. Plastics provide a durable substrate that can be colonized by micro and macro-organisms. They support the growth of potential pathogens and HAB species. Further, plastic debris has been considered to play a key role in the dispersal also of biotoxins. The present study aimed to investigate harmful phytoplankton assemblages that colonized numerous samples of micro and macro-plastics collected in the Mediterranean Sea by qPCR assays, and to forecast toxin dispersal by quantifying toxin content onto plastic debris. Further, the impact of polystyrene nanoparticles (PS NPs) to the HA diatom Skeletonema marinoi was analyzed. All plastic samples were positive for the presence of Dinophyceae and Bacillariophyceae communities and some plastic samples were colonized by toxic species of dinoflagellate Alexandrium pacificum, Alexandrium minutum, Ostreopsis cf. ovata and diatom Pseudo-nitzschia spp. Strains of A. pacificum isolated from plastic debris and analyzed by LCHRMS produced PST (paralytic shellfish toxins). The levels of potential toxins on plastic samples ranged from 101 to 102 ng cm-2. The interactions between HA diatom and plastic nanoparticles demonstrated an increase of both extracellular and intracellular reactive oxygen species, and significantly reduced colonies length using TEM and SEM techniques. Then, plastics can negatively impact the ecological functioning of oceans. The potential risk of harmful microalgae dispersal associated with plastic pollution was illustrated as well as for chemical compounds to transfer through the trophic chain with implications for human health and marine ecosystem.