fStraps, buckets, bags, packaging foil, toothbrushes, broken toys, old ropes and fishing nets – huge amounts of plastic waste are floating in the oceans. They don’t just mess up the beaches. More and more sea creatures are dying because they get tangled in plastic parts, strangle themselves with them or swallow them. But there is not only this obvious threat: the smaller the pieces of plastic, the greater the risk that they will be swallowed and accumulate in the animals’ bodies.
A current finding by American scientists from Stanford University is alarming in this context. They found that blue, humpback and other baleen whales ingest large amounts of microplastics in the food they filter out of the water. In the case of blue whales, the largest animals on earth, it is estimated that around ten million pieces of plastic are lost every day.
Plastic particles smaller than five millimeters are called microplastics. The concentration of the tiny particles, which come from car tires, synthetic clothing or packaging material, for example, is particularly high in a water depth of 50 to 250 meters, the researchers led by Mathew Savoca write in “Nature Communications”. At this depth, the baleen whales prefer to forage, and according to the researchers, they ingest almost all plastic particles from their prey, such as krill or small fish. In these, the particles accumulate over time.
Humpback whales, which feed primarily on herring and anchovies, would ingest an estimated 200,000 pieces of microplastics per day, while marine mammals, which primarily eat krill, ingest at least a million pieces. Fin whales, which feed on both krill and fish, are estimated to three to ten million microplastic parts ingest per day. “Consumption rates are likely even higher for whales living in more polluted regions like the Mediterranean,” says Matthew Savoca.
For their study, the researchers combined measurements of microplastic concentrations, which they took along the coast of California, with data from whales that had been looking for food there. The marine mammals had previously been equipped with tracking devices. Due to the large amount of contaminated food, the researchers refer to possible risks and stress factors for the giant marine mammals. Further investigations, for example into the health risks from the consumption of plastic particles, are necessary.
Sea snow as a transport vehicle for microplastics
In this context, a study by marine biologists from the Geomar research center in Kiel provides important information on how microplastics in the oceans get into the food chain. A research team led by Luisa Galgani has discovered that plastic particles are transported from the sea surface to deeper water layers with sinking “sea snow”. The researchers refer to organic material that serves as food for plankton and larger sea creatures as sea snow sinks into the depths.
Galgani and her colleagues analyzed samples they collected three years ago during an expedition off the Azores with the research ship Poseidon. The researchers found the greatest concentration of microplastics at depths of between 100 and 150 meters, as reported in the journal “Environmental Science and Technology”. Some of the particles would be absorbed by living things together with the sea snow and thus enter the nutrient cycle. In this way, the microplastics accumulate in the gastrointestinal tract of the baleen whales, which filter the contaminated microorganisms out of the water.
Every year, the amount of plastic in the world’s oceans increases by around six million tons. That is about as much as was produced worldwide in 1960. The rubbish comes from objects carelessly thrown overboard, from flotsam from deep-sea fishing or from objects that are washed down the sewage system into the rivers and finally into the sea. While paper, wood and even Coke cans decompose sooner or later, plastic doesn’t rot. At best, it is worn down by mechanical processes and weathering until microscopic particles remain. Marine biologists have long feared the devastating consequences for the marine ecosystem.