The terrestrial megafauna that once populated the planet, such as mastodons, woolly rhinoceroses and giant sloths, is now extinct, and the marine megafauna that still survives risks meeting the same fate. The decline of large land animals was caused by the growing spread of a super-predator, Homo sapiens, while the great ocean creatures, such as mysticetes, whale sharks, basking sharks and manta rays are threatened by a insidious enemy that is almost invisible (also linked to the advent of humans): microplastics.

Plankton and plastic

According to the study Microplastics: No small problem for filter-feeding megafauna, published in the journal Trends in Ecology & Evolution, marine animals that feed on plankton by filtering seawater ingest large quantities of microplastics that can prevent them from absorbing nutrients and cause other serious side effects.

What microplastics are

So-called microplastics are plastic particles measuring less than five millimetres that come from the fragmentation of waste dispersed in the environment, but can also be a primary waste product. The true scale of the problem is not yet clear, precisely because of the small size of this waste, but their presence is heavily affecting not only the marine ecosystem but also freshwater and river ecosystems.

Large marine animals at risk

The effects of microplastics on marine fauna are also still little studied, but they could be no less harmful than the conventional plastic waste that infests the oceans across the globe. "Despite the growing body of research on microplastics in the marine environment, we are still trying to understand the scale of the problem," said the study's lead author, Elitza Germanov, a researcher at the Marine Megafauna Foundation. "It is now clear, however, that microplastic contamination can drastically reduce populations of large filter feeders, which reproduce slowly and are already threatened by other problems."

The toxic effects of microplastics

The study, conducted by a group of researchers from the Marine Megafauna Foundation at Australia's Murdoch University, the Hawaii Institute of Marine Biology and the University of Siena, hypothesises that microplastics transmit toxins to the animals that ingest them. Plastic fragments would therefore not have lethal effects on sharks and whales, but "sublethal" ones, as explained by Maria Cristina Fossi, professor at the University of Siena and co-author of the study, which could seriously compromise the animals' health once they reach their digestive systems. "Exposure to these toxins poses a serious health threat to these animals as it can disrupt the hormones that regulate growth, development, metabolism and reproductive functions," Maria Cristina Fossi told the British newspaper the Guardian.

Elitza Germanov, PhD @AliceInWaterlnd

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Invisible pollution

The research has therefore highlighted that even in apparently cleaner oceans a serious plastic pollution problem lurks beneath the surface. "We analysed the Sea of Cortez, in California, and calculated a presence of 0.7 plastic fragments per cubic metre," said the Italian researcher. "A whale shark can therefore ingest around 170 plastic particles per day."