According to a new study, microplastic pollution can put filter-feeding animals such as manta rays and whale sharks at risk.
Researchers are still determining to what extent small pieces of plastic can impact marine life and ecosystems over the long term.
The study, published in the journal Trends in Ecology & Evolution, by researchers from the Marine Megafauna Foundation, Murdoch University (Australia), University of Siena (Italy) and Hawaiʻi Institute of Marine Biology, stresses the significant risks microplastics pose to megafauna since these need to swallow hundreds to thousands of cubic meters of water daily in effort to capture plankton. Ingesting large amounts of plastic, either directly from polluted water or indirectly through contaminated prey, puts these animals, which also includes whales, at risk of exposure to contamination and associated toxins.
Researchers found that indigestible plastic particles can block nutrient absorption and cause damage to the digestive tract of animals. Additionally, plastic-associated chemicals and pollutants can accumulate over decades and alter biological processes, leading to altered growth, development and reproduction, including reduced fertility.
“Despite the growing research on microplastics in the marine environment, there are only few studies that examine the effects on large filter feeders,” Marine Megafauna Foundation researcher Elitza Germanov said. “We are still trying to understand the magnitude of the issue. It has become clear though that microplastic contamination has the potential to further reduce the population numbers of these species, many of which are long-lived and have few offspring throughout their lives.”
The study relied on non-lethal sampling of small amounts of tissue (biopsy) to test for chemical tracers.
“It is vital to understand the effects of microplastic pollution on ocean giants since 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 prioritized for conservation,” she said.
The researchers estimated that whale sharks may be ingesting nearly 200 pieces of plastic on a daily basis.
“Our studies on whale sharks in the Sea of Cortez and on fin whales in the Mediterranean Sea confirmed exposure to toxic chemicals, indicating that these filter feeders are taking up microplastics in their feeding grounds. Exposure to plastic-associated toxins pose a major threat to the health of these animals since it can alter the hormones which regulate the body’s growth and development, metabolism, and reproductive functions, among other things,” Study co-author Maria Cristina Foss said.
Filter feeders are considered to be at high risk of exposure since many inhabit some of the most polluted waters, namely in the Coral Triangle region, Bay of Bengal, Gulf of Mexico and Mediterranean Sea.
“As plastic production is projected to increase globally, future research should focus on coastal regions where microplastic pollution overlaps with the critical feeding and breeding grounds of these threatened animals,” Germanov said. “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.”
