Master of Marine Conservation graduate Rachel Parry and Professor James Bell from the University’s Te Kura Mātauranga Koiora—School of Biological Sciences conducted the study, which took samples from sponges at three sites in Wellington Harbour.
"Sponges are filter feeders, meaning they suck in water and capture small particles to eat,” says Professor Bell. “Unfortunately, this includes tiny pieces of plastic. And if it’s happening to our sponges, it’s likely happening to other filter feeders like mussels and clams.”
Microplastics are defined as particles smaller than 5 mm that originate directly from manufacturing processes. This includes purpose-built micro pellets used in cosmetics, or pieces of plastic waste that have broken down over time. The small size of the particles makes them easily ingestible for sea sponges, as they’re the same size as the sponges’ regular food.
Professor Bell says the findings show how widespread microplastics have become in the environment.
Master’s student Rachel Parry completed the research as part of her studies. She says the ingestion of microplastics pose a significant threat to sponge health.
“Once ingested they can’t be digested or absorbed. These plastics can also carry toxic chemical additives, which can leech into organisms.”
The team found that the amount of microplastic in sponges depended more on the location where the sponges were collected from than the species of sponge.
Microplastic levels in sponges were highest in samples from Evans Bay, followed by Mahanga Bay, with the lowest levels in Shark Bay.
Rachel says the most surprising finding from the research is the sheer amount of microplastic within the sponges.
“There were thousands of particles in some samples.
“It highlights how critical and urgent the need is to protect our oceans and our seafood from plastic from plastic pollution.”
Professor Bell’s previous research has examined sponge feeding, but this is the first time he has focused specifically on plastic in sponges.
“At present we don’t know what the impact of these plastic particles will be on sponges themselves, since this is an emerging field with only a handful of studies globally reporting plastic in sponges.
“But anything feeding on sponges is also likely to consume these particles, so will likely be moving up the food chain.”