Microplastics and Nanoplastics in Okinawa: Potential Impacts on Planktonic Microalgae and Endosymbiotic Dinoflagellates

From coast to gyre, from surface to deep sea, the study of marine plastic pollution takes us on a journey of potential harm through our marine ecosystems, where man-made plastics break down into ever smaller pieces along their way. Studying micro- and nanoplastic pollution in field and laboratory work, new insights into microalgae interactions, and these smallest plastic particles were gathered. Mimicking two different environments in the laboratory - reef and open ocean water - an effect assessment of four different microalgae species (Diatoms Skeletonema grethae and Odontella aurita, cyanobaterium Synechococcus elongatus, endosymbiontic dinoflagellates Symbiodinium tridacnidorum and Cladocopium sp.) and their interaction with micro- and nanoplastics at different sizes, types, and concentrations was conducted. Aggregation, sedimentation, photosynthesis, extracellular substance production, and RNA expression patterns were all found to be affected. Specifically, hetero-aggregation with nanoplastic led to neutrally buoyant marine snow, differentially expressed genes, and reduced photosynthesis. Furthermore, an exposure assessment around Okinawa, an isolated subtropical island with fringing reefs, found that microplastic pollution follows the island’s population gradient. Polyethylene was the most abundant polymer found 45%, and of the ubiquitous sub 20 μm plastics, the majority was embedded in organic matter.