Plastics threat to filter-feeders

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Plastics threat to filter-feeders

Amid current concerns about the effects of microplastics on marine mammals, fish and birds, the extent of the threat to large filter-feeding animals has not been fully recognised until now.

This is according to a new study claiming that plastics pollution poses additional risks to animals such as manta rays, whale sharks and baleen whales.

These filter-feeders are considered to be at high risk of exposure because many of them inhabit some of the most polluted waters, such as the Coral Triangle, Bay of Bengal, Gulf of Mexico and Mediterranean Sea.

Researchers from the Marine Megafauna Foundation (MMF), Murdoch University in Australia, the University of Siena and Hawaii Institute of Marine Biology say that these megafauna swallow hundreds to thousands of cubic metres of water daily to capture plankton and are therefore ingesting microplastics both directly from polluted water or indirectly through contaminated prey.

This can block nutrient absorption and damage their digestive tracts in the short term, while over decades the cumulative effects can alter growth, development and reproduction, including reducing fertility.

Researchers from the University of Siena reported an average of 0.7 plastic items per cubic metre of water around the whale-shark feeding grounds off the Baja California peninsula, and estimated that the animals could be ingesting 171 items a day, while fin whales in the Mediterranean were thought to be swallowing thousands of microplastics particles daily.

Lead author Elitza Germanov of the MMF and Murdoch University said that although there had been few previous studies it had become clear that microplastics contamination could further reduce populations of species that have few offspring throughout their long lives.

“Nearly half of the mobulid rays, two-thirds of filter-feeding sharks and over one quarter of baleen whales are listed by the IUCN as globally threatened species and are prioritised for conservation,” she said.

“Future research should focus on coastal regions where microplastics pollution overlaps with the critical feeding and breeding grounds of these threatened animals. Many areas are biodiversity hotspots and of economic importance due to fisheries and marine tourism.

“Targeting these with the backing of local government and industry will help ensure efforts to mitigate the plastic threat are employed to their fullest.”

The study is published in Trends in Ecology & Evolution here

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