Algae showed a 50% decline in net photosynthesis when exposed to higher levels of microplastic pollution.
Microplastics affect the ability of algae to produce energy
Microplastics are insidious. These tiny particles are virtually everywhere on earth, causing all manner of harm in the environment both on land and in water.
Microplastics affect even the workings of small organisms by reducing their ability to photosynthesize and thereby produce energy and release oxygen, which could have great implications for biodiversity.
A scientist at the University of Exeter discovered this after testing whether microplastic contamination in water affects the symbiotic relationship between Paramecium bursaria, a species of ciliate, and a green algae called Zoochlorella.
He found that the algae showed a 50% decline in net photosynthesis when exposed to higher levels of microplastic pollution. Why this happens has yet to be explained, but one possibility is that Paramecium bursaria ingest plastic particles or chemicals from the plastics, which affects their biological processes.
“The relationship I examined, known as photosymbiosis, is commonly found both in freshwater and the oceans,” explains Ben Makin, an associate researcher at the Environment and Sustainability Institute in Cornwall who was the lead author of a study.
“Recent studies have shown that microplastics (plastic particles smaller than 5 mm) may interfere with photosymbiosis, but more research is needed, especially in freshwater habitats,” Makin says. “Paramecium bursaria are found in freshwater around the world, and similar symbiotic relationships exist in the oceans.”
Makin placed Paramecium bursaria in water contaminated with microplastics at levels higher than that usually seen in nature but not unprecedented in its scale.
“At this stage, the question I wanted to answer was whether severe contamination could affect this important relationship and what those effects might be,” Makin says.
The scientist tracked the impacts of microplastics on growth rate, symbiont density (how many algae were in each Paramecium bursaria), metabolic rate, feeding rate and net photosynthesis.
“Only net photosynthesis was significantly affected, but this could be important as it provides the organism with energy and underpins the ‘trade’ in nutrients that allows the photosymbiosis to persist,” the expert says.
“The findings could raise concern for the important contributions of photosymbiosis to primary production at a global level,” Makin observes. “Microplastics are a widespread contaminant, and their impacts on photosymbiosis, especially in freshwater, remain quite poorly characterised.”
More research is needed, he says, to test different microplastic concentrations as well as various kinds of plastic and their effects on different species of aquatic organisms.
