Microplastics a 'risk to filter feeders'

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Photo by Elitza Germanov Bottom feeders like the manta ray may be at risk because of microplastics.

An Australian marine scientist says microplastics in the oceans pose a "significant risk" to filter-feeding marine animals like manta rays and whale sharks.

A research paper, "Microplastics: No small problem for filter feeding megafauna," was published in the Feb. 5 issue of the journal Trends in Ecology & Evolution.

Lead researcher Elitza Germanov, from Murdoch University in Perth, said microplastics are hazardous for filter feeders because they contain toxic chemicals.

"Plastic-associated chemicals and pollutants can accumulate over decades and alter biological processes in the animals, leading to altered growth, development and reproduction, including reduced fertility," she said.

"While a definitive connection between microplastic ingestion and toxin exposure for filter feeders remains to be confirmed, studies into sea birds and small fish have found a link," Germanov said.

"Marine filter feeders are likely to be at risk because they need to swallow hundreds to thousands of cubic meters of water daily to capture plankton. They can ingest microplastics directly from polluted water or indirectly through contaminated prey."

Germanov said despite growing research on microplastics in the marine environment, few studies 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 use non-lethal sampling of small amounts of tissue, which we test for chemical traces using sophisticated and sensitive analytical tools."

Study co-author Professor Maria Cristina Fossi, from the University of Siena in Italy, said her studies on whale sharks in the Gulf of California and fin whales in the Mediterranean Sea confirm 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.

Fossi said filter feeders congregate in "habitats which overlap with microplastic pollution hotspots, including the Gulf of Mexico, the Mediterranean Sea, the Bay of Bengal and the Coral Triangle, which is the marine area comprising the waters of south-east Asian countries, including Indonesia."

The paper said indigestible plastic particles may damage filter-feeder animals' digestive systems.

Germanov said microplastic contamination has the potential to reduce population numbers of filter feeders, many of which are long-lived species and have few offspring throughout their lives.

Several filter feeder species are listed by the International Union for Conservation of Nature as globally threatened species and are prioritised for conservation.

"As plastic production is projected to increase globally, long-term monitoring programs are needed in the feeding grounds of these ocean giants, so we can check on toxicity levels in these creatures over time," Germanov said.

"Microplastics potentially place the viability of nature-based tourism involving these creatures under threat. This kind of tourism is a significant source of income in regions where filter feeders congregate," she said.


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