Plastic-associated harmful microalgal assemblages in marine environment

Marine plastics are abundant in the most marine surface waters and known to transport fouling harmful microorganisms that potentially play key roles of dispersal and ecological impacts of pollution. Plastic marine debris collected at several sites in the Mediterranean Sea were analyzed using molecular qPCR assay to characterize and quantify the attached phytoplankton taxa, and in particular, harmful algal species. We detected and quantify the attached Bacillariophyceae and Dinophyceae classes, as well as we estimated the abundance of several harmful dinoflagellate species on the plastic debris surfaces. The maximum abundance of diatoms and dinoflagellates recovered amounted to 8.1 x 104 and 1.0 x 103 cells cm2 of plastic debris, respectively. Then, among which, the more abundant harmful species was the toxic dinoflagellate Ostreopsis cf. ovata producing ovatoxins and palytoxin compounds with 260 cells cm2, whereas the more frequent toxic dinoflagellate were Alexandrium pacificum, A. minutum, O. cf. ovata and Lingulodinium polyedrum with 38% and 21% of presence on the plastic debris for the first and latter species, respectively. These findings infer important considerations on how anthropic impact of plastic debris dispersal in the sea can create micro-environments for toxic microrganisms proliferations and dispersion. The epi-plastic community can therefore, affect the harmful level of plastics by dispersion, alien species carrier and ingestion by macro-organisms.