VAST AMOUNTS OF of plastic debris floating in the ocean are supporting new forms of microscopic life and whole new ecosystems. Scientists writing in the journal Environmental Science & Technology are collectively calling this new life the ‘plastisphere’. Previous studies have thoroughly outlined the harmful effects of plastic on animals such as fish, birds and other forms of marine life. However, none had fully assessed the effects of plastic on microscopic ocean dwellers. The team, which included Tracy Mincer at the Woods Hole Oceanographic Institution in Massachusetts and Linda Amaral-Zettler of the Marine Biological Laboratory in Woods Hole, used fine mesh nets to collect pieces of plastic — around 1 to 5mm in diameter — from sites in the North Atlantic Ocean. Using a combination of high-resolution imaging and genetic sequencing, they discovered unique ecosystems living on two kinds of plastic, with communities composed of microbes that are genetically distinct from those on other natural surfaces in the surrounding waters, such as driftwood or feathers. The plastic communities were also more diverse than those in seawater samples, which are typically dominated by only a few species. “The organisms inhabiting the plastisphere were different from those in surrounding seawater, indicating that plastic debris acts as artificial ‘microbial reefs’,” said Mincer. “They supply a place that selects for and supports distinct microbes to settle and succeed.”
More than 1,000 species of microbes were found in the study, including plants, algae and bacteria, some of which remain unidentified. These communities typically had a natural order: with plant-like organisms at the bottom of the food chain and higher order creatures that feed on them. Other organisms that live in harmonious relationships with each other were also identified.
“We’re not just interested in who’s there. We’re interested in their function, how they’re functioning in this ecosystem, how they’re altering this ecosystem, and what’s the ultimate fate of these particles in the ocean,” said Amaral-Zettler. “Are they sinking to the bottom of the ocean? Are they being ingested? If they’re being ingested, what impact does that have?”
Electron microscope images also reveal that some bacterial members of the plastisphere were nestled in ‘pits’ on the plastic surface, supporting the idea that these organisms may actually be contributing to the degradation of the plastic.
Studies conducted over the last 22 years found that despite an increase in the production of plastics, the amount of plastic oceanic debris has remained relatively stable. The scientists hope that ‘pit formers’ are breaking down the plastic, though they caution that more experiments need to be conducted.
“When we first saw the ‘pit formers’ we were very excited, especially when they showed up on multiple pieces of plastic of different types of resins,” said Zettler. “Now we have to figure out what they are by sequencing them and hopefully getting them into culture so we can do experiments.”
As the research is in its infancy, it is difficult to speculate yet about the potential effects of the emerging plastisphere on marine ecological environments.
Researchers are concerned that as the plastics, along with the unique micro-organisms they harbour, drift widely they have the potential to act as vectors for dispersal of harmful pest species or pollutants.
Penny Orbell wrote this article as part of her science communication studies at the University of Melbourne. From abc.net.au