Researchers from The University of Western Australia said there were huge numbers of floating plastics at sea and their study was the first to document biological communities on pieces from Australian waters.
The tiny ocean plastics come from the breakdown of discarded plastic items, such as single-use packaging and fishing gear.
More than 1,000 images were taken while examining ocean plastics from Australia-wide sample collections using a scanning electron microscope at UWA's Centre for Microscopy, Characterisation and Analysis, researchers said.
Study co-author Dr Jeremy Shaw said large numbers of silica-forming algae weighed down their plastic host, potentially causing tiny pieces to sink to the bottom of the ocean.
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The researchers were also able to see colonies of microbes that seem to be "eating plastics".
"Plastic biodegradation seems to happen at sea. I am excited about this because the 'plastic-eating' microbes could provide solutions for better waste disposal practices on land," researcher Julia Reisser said.
However, Reisser said "epiplastic" organisms could also make ocean plastics more attractive as food for animals, inducing plastic ingestion and negative impacts.