‘Plastics, rising CO2 levels posing combined threat to marine environment’

An international team of researchers has found that the combined environmental threat of plastic pollution and ocean acidification are having significant impacts on species living in our oceans.

The study, published in the journal Marine Pollution Bulletin, found that after three weeks of being submerged in the ocean, the bacterial diversity on plastic bottles was twice as great as on samples collected from the surrounding seawater.

However, in areas of elevated carbon dioxide, a large number of taxonomic groups - including bacteria that play an important role in carbon cycling - were negatively impacted.

The research also showed that while many groups of bacteria were shared between plastic, free-living and particle-associated samples, almost 350 were found uniquely on plastics.

"The study adds to growing evidence that the increasing presence of plastic marine debris is providing a novel habitat for bacteria," said study authors from University of Tsukuba in Japan.

However, their results highlight that environmental conditions and local ecological processes will play an important role in determining its broader impact over the coming decades.

Scientists submerged a number of plastic bottles in seas off the Japanese Island of Shikine, a region renowned for its CO2 seeps where the escaping gas dissolves into the seawater and creates conditions similar to that expected to occur worldwide in coming years.

They then used a combination of DNA sequencing and statistical techniques to analyse how bacteria colonise the plastic in comparison to the surrounding natural environment, and whether the increased CO2 levels would cause changes in the bacteria's distribution.

"Discarded plastic drinking bottles have become a common sight in our oceans and we were expecting to see them being colonised by different types of bacteria," said study lead author Ben Harve from the University of Tsukuba.

"We also predicted that raised CO2 levels would cause significant changes in the bacterial colonies, but it was still surprising to see the extent of that change and how the raised levels affected species differently," Harve added.

To see beneficial species dwindling while harmful species thrive is an obvious present and future cause for concern, according to the researchers.

Researchers from Tsukuba, Plymouth and other collaborators have published several studies over the past decade showing the threats posed by ocean acidification in terms of habitat degradation and a loss of biodiversity.