Marine plastic pollution is an increasing environmental threat, with microplastic accumulating in oceans and seas around the world.
A study conducted in a molecular ecology laboratory reveals an intriguing phenomenon in the eastern Mediterranean Sea.
On floating plastic particles in the water, there is a unique ecological system that is different from the surrounding seawater and rich in microscopic algae called diatoms.
In recent decades, the problem of marine plastic pollution has grown steadily.
Large waste breaks down over time into tiny particles known as microplastic.
These particles accumulate in oceans across the globe especially in enclosed seas surrounded by densely populated regions.
Floating plastic particles do not remain empty.
They serve as a solid surface on which complex communities of bacteria, fungi and other tiny organisms develop.
This system referred to in the past decade as the plastisphere, is considered a unique ecological environment created by human activity.
In a study that lasted two years and was published in the journals Scientific Reports and Jeju Journal of Island Sciences, researchers sampled microplastic at the sea surface about one kilometer offshore. The samples were analyzed using advanced genetic sequencing methods and a scanning electron microscope.
Dozens of species of microscopic diatoms that settled on the plastic particles were identified.
Diatoms, one of the most important and widespread groups in the oceans, are single celled algae with a silica shell decorated with intricate patterns.
They form a central part of the marine food chain and contribute significantly to the production of oxygen on Earth.
They are responsible for about 40 percent of primary production in the oceans and nearly a quarter of the oxygen in the atmosphere.
On average, almost every fourth breath humans take contains oxygen produced by diatoms.
Another finding from the study is that most of the diatoms that settled on the plastic were species of the Pennate type, benthic species that usually live on the seafloor where they attach to hard surfaces. In contrast, diatoms in open seawater are usually of the Centric type, which have a circular symmetrical shape and live in a floating state.
The fact that benthic diatoms were found on floating plastic particles indicates that human waste has created a new ecological niche.
The plastic particles provide a stable surface and high exposure to sunlight allowing these algae to thrive even in waters that are poor in nutrients such as those of the eastern Mediterranean Sea.
During the summer a season in which water temperature, light intensity and day length reach their peak, the concentration of algae on the plastic reached its highest levels.
According to the researchers, the high presence of diatoms on plastic particles may influence major biogeochemical cycles in the sea.
When the algae grow and multiply, they incorporate carbon in their bodies from the carbon dioxide present in the water and air.
After they die, their heavy silica shells sink to the seafloor, transferring carbon from the atmosphere to the deep ocean.
This process reduces the concentration of carbon dioxide in the atmosphere and can help slow the pace of climate warming.
The process is known as the biological pump, but the picture is even more complex. Layers of algae may weigh down the plastic and cause it to sink.
After the algae decompose, the plastic may rise again to the surface and be recolonized by a new community of marine microorganisms.
The findings from the Mediterranean Sea add to global evidence that marine plastic waste is not only an environmental problem but also an active ecological factor reshaping marine life systems.
Plastic has become a major environmental element that changes the biological structure of the sea, and researchers believe that its impact is only beginning to be understood.