According to a new analysis for the journal Trends in Ecology & Evolution, microplastics in our oceans are posing a significant risk to filter-feeding marine animals like manta rays and whale sharks.
Microplastics are small plastic pieces less than five millimetres long . If you’ve ever bought a shower scrub, or exfoliator, you’ve probably heard of microbeads too. Microbeads are a type of microplastic, and are very tiny pieces of manufactured polyethylene plastic that are added as exfoliants to health and beauty products, such as some cleansers and toothpastes.
Led by Murdoch University PhD student Elitza Germanov, the study warns that microplastics could be hazardous because they contain toxic chemicals. These chemicals and pollutants can accumulate over time and impede on biological processes in the animals, leading to stunted growth, development, and reproduction, as well as reduced fertility.
Although a definitive connection between microplastic ingestion and toxin exposure for filter feeders (such as clams, krill, sponges, baleen whales, and many fish) remains to be confirmed, studies into sea birds and small fish have found a link, Ms Germanov says.
These filter feeders are likely to be at risk because they swallow hundreds to thousands of cubic metres of water daily in order to capture plankton. They can ingest microplastics directly from polluted water or indirectly through contaminated prey.
These species also tend to inhabit oceans and seas which overlap with microplastic pollution hotspots, including the Gulf of Mexico, the Bay of Bengal ,the Mediterranean Sea, and the Coral Triangle, which is the marine area comprising the waters of South East Asian countries including Indonesia.
According to the analysis, these indigestible plastic particles may damage the digestive systems of these iconic species.
Ms Germanov said scientists are still trying to understand the magnitude of the microplastics problem:
“Despite the growing research on microplastics in the marine environment, there are only a few studies that examine the effects on large filter feeders. This is because it is difficult to assess plastic concentrations via conventional methods such as stomach analysis, because these are unsuitable for threatened species like whale sharks and manta rays.”
“So we are using non-lethal sampling of small amounts of tissue, which we are testing for chemical tracers using sophisticated and sensitive analytical tools.
“I am working with Murdoch’s Separation Science and Metabolomics Laboratory to understand how levels of plastic associated toxins such as pesticides and industrial chemicals are building up in manta rays and whale sharks.”
Co-author Professor Maria Cristina Fossi from the University of Siena in Italy, said her studies on fin whales in the Mediterranean Sea and whale sharks in the Gulf of California confirmed exposure to toxic chemicals.
“As these areas are hotspots for microplastics, our results could indicate that filter feeders are taking up microplastics in their feeding grounds,” she said.
Additionally, microplastic contamination has the potential to reduce population numbers of filter feeding animals, many of which are long-lived and have few offspring throughout their lives.
Several species of filter feeders are listed by the IUCN (International Union for Conservation of Nature) as globally threatened species and are prioritised for conservation. Understanding the effects of microplastic contamination through long-term metabolomics studies will help to shed light on the health of filter feeding species in response to plastic-associated toxins.
“As plastic production is projected to increase globally, the establishment of long-term monitoring programs is needed in the feeding grounds of these ocean giants, so we can check on toxicity levels in these creatures over a period of time,” Ms Germanov said.
“The microplastics issue potentially places the viability of nature based tourism involving these creatures under threat also. This kind of tourism is a significant source of income in the regions where filter feeders congregate.
“Raising awareness of this issue in communities, among governing bodies and industries could help to change behaviours around the production, management and use of plastics.”