Plastic pollution is damaging freshwater species worldwide

By Stephen Beech via SWNS

Plastic pollution reduces energy production in a microscopic creature vital to the health of freshwater species worldwide, warns new research.

Scientists found that tiny microplastics - particles smaller than five millimeters - inhibit paramecium bursaria which contain algae that live inside their cells and provide energy by photosynthesis.

The University of Exeter study tested whether severe microplastic contamination in the water affected the symbiotic relationship.

The results showed a decline of 50 percent in net photosynthesis – a major impact on the algae’s ability to produce energy and release oxygen.

Study lead author Dr. Ben Makin said: "The relationship I examined – known as photosymbiosis – is commonly found both in freshwater and the oceans.

“We know climate change can damage photosymbiotic relationships, including in corals - leading to ‘bleaching’ events.

“Recent studies have shown that microplastics may also interfere with photosymbiosis – but more research is needed, especially in freshwater habitats.

“In this study, I chose a ‘classic’ example of photosymbiosis – Paramecium bursaria are found in freshwater around the world, and similar symbiotic relationships exist in the oceans.”

The study placed Paramecium bursaria in water contaminated with microplastics in the lab. The level of contamination was higher than that usually seen in the natural world, but it has been found in some places.

Dr. Makin said: “At this stage, the question I wanted to answer was whether severe contamination could affect this important relationship – and what those effects might be.

“This is a pilot experiment, and more research is needed to test different microplastic concentrations, different kinds of plastic and the effects on different species.”

The findings, published in the journal Aquatic Biology, do not reveal how microplastics caused the observed impacts on photosymbiosis.

Dr. Makin said that possibilities include Paramecium bursaria ingesting plastic particles, and/or chemicals from the plastics affecting biological processes.

The study tracked the impact 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 the research team said that that could be important, as it provides the organism with energy and underpins the “trade” in nutrients that allows the photosymbiosis to persist.

Roughly half of all photosynthesis in the ocean is underpinned by photosymbiosis, according to the researchers.

Dr. Makin added: “The findings could raise concern for the important contributions of photosymbiosis to primary production at a global level.

“Microplastics are a widespread contaminant, and their impacts on photosymbiosis – especially in freshwater – remain quite poorly characterized.”