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Scientists have discovered that substances resembling glue secreted by bacteria stick tiny particles of plastic in the ocean to form larger mbades.
During experiments in seawater, micro and nano plastics have joined biopolymers made by bacteria to form larger clumps in minutes.
Scientists believe this could lead marine mammals to confuse larger items with food.
They also fear that this will alter the flow of food from the surface to the bottom of the sea, which could lead to the death of deep sea creatures.
Researchers at Heriot-Watt University in Edinburgh used water from the Faroe-Shetland Cbad and the Firth of Forth to set up their experiments.
Plastics were added to seawater and then incubated under conditions simulating the ocean surface.
In minutes, the tiny pieces of plastic clustered with bacteria, algae and other organic particles.
Scientists would have been surprised to discover that large mbades of biopolymers formed the bulk of these plastic agglomerates.
Team member Stephen Summers said, "This is a first step towards understanding the interaction of nanoplastics with natural biopolymers in the world's oceans.
"This is very important because it is at this small scale that much of the world's biogeochemistry is occurring.
"We found that biopolymers enveloped or engulfed nanoplastic particles, which caused the agglomeration of plastics in blocks.
"Nanoplastics, which are 100 to 200 times smaller than a bacterial cell, have actually been incorporated into agglomerates, which has become visible to the naked eye during our laboratory experiments.
"The fact that these agglomerates become large enough to be perceived is a concern because they are likely to be considered a source of food by small marine animals."
Tony Gutierrez, the microbial ecologist who led the study, outlined his concerns about the potential impact on deep seabed and geochemical cycles.
He said: "The agglomerates form a kind of marine snow, a shower of organic detritus that transports carbon and nutrients from the surface to the bottom of the ocean and feeds deep – sea ecosystems.
"It will be interesting to understand if nanoscale and microscopic scale plastics of different densities could affect the flow of food from the top to the bottom of the ocean.
"Heavier plastics could cause marine snow to fall more quickly on the sea floor, while the reverse could occur with lighter plastic shapes making it more fluttering and falling more slowly.
"In this case, deep-water ecosystems could become deprived of food.
"To understand this scenario, we need data on the abundance of these invisible plastics in the ocean."
Ted Henry, professor at Heriot-Watt, said the larger mbades were "much more complex than just pieces of plastic."
He added, "Research like this is beginning to fill the gaps in scientists' knowledge, but we need more evidence to prioritize and effectively manage plastic pollution."
The experiments were part of the RealRiskNano project of the Council for Natural Environment Research, worth £ 1.1 million, and the results of this research were published in the Marine Pollution Bulletin.
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