How Microplastics Travel from Krill to Whales

Dear readers, in continuation of my article from last week, let us once again follow the krill and understand not only how they consume their food but also how they end up ingesting microplastic particles along the way. But before we get to that, it is important to first understand the very basics of the aquatic food chain, because that is where this story truly begins.

In all kinds of aquatic ecosystems—whether oceans, seas, lakes, or rivers—there exist extremely tiny microscopic organisms known as phytoplankton. These are mostly microscopic algae, invisible to the naked eye, yet they play an enormous role in sustaining life in water. In fact, they form the very base or foundation of an intricate and interconnected aquatic food chain and food web.

Phytoplankton are remarkable because they can make their own food. Using water, carbon dioxide, and energy from sunlight, they produce nutrients through photosynthesis and, in the process, release oxygen into the environment. This makes them the primary “producers” in aquatic ecosystems, supplying both food and oxygen that support life at every higher level of the chain.

Countless marine and freshwater species, directly or indirectly, depend on these primary producers for survival. In simple terms, the aquatic food chain begins with phytoplankton. The next level consists of zooplankton, which include krill and other tiny drifting sea creatures. These are known as primary “consumers” because they feed on phytoplankton.

These zooplankton are then eaten by small fish and other marine animals, which become secondary consumers. In turn, they are preyed upon by larger fish and other predators, forming tertiary consumers and higher levels of the food chain. As we move upward, the food chain becomes longer, more complex, and more interconnected.

At the very top of this chain are the apex predators—whales, other marine mammals, seabirds, and, ultimately, we humans. And this is precisely why what happens at the microscopic level, beginning with phytoplankton and krill, matters so deeply to all life above them.

Microplastics and Whales

Microplastic particles, though tiny, can easily cling to the outer surface of phytoplankton and may even enter their cellular structure over time. In other words, a single algal cell can end up carrying multiple microplastic particles within or around it. What appears insignificant at the microscopic level becomes alarming when we look at what happens next in the food chain.

Let us do a simple calculation. A krill, shrimp, or any other small aquatic “consumer” can ingest thousands of these algal cells in a single feeding. If we assume that each algal cell carries around 50 microplastic particles, then a krill consuming 1,000 such cells in one go could take in as many as 50,000 microplastic particles. That is an astonishing number for such a tiny creature.

Now take the next step. Imagine a whale consuming 1,000 such krill, each already carrying 50,000 microplastic particles. In that one feeding event alone, the whale could potentially ingest 5 crore microplastic particles. And in reality, a whale can swallow thousands of krill at once. This gives us a disturbing glimpse into the sheer volume of microplastics that can enter the body of a single large marine animal in a very short span of time.

And this is not just about whales. There are thousands of species of fish and other marine animals that feed either directly on phytoplankton or on these primary consumers, such as krill. This means microplastics are steadily moving upward through the marine food chain, entering the bodies of species large and small.

No matter which animal is affected, microplastics are foreign intruders in the body and can pose a serious threat to overall health. In whales, dolphins, and other large marine mammals, these particles can cause internal damage by irritating or scratching the stomach lining, sometimes contributing to infection, poor nutrition, or even starvation. These mammals often consume prey that has already accumulated microplastics, especially from ocean depths between 50 and 250 metres, where concentrations are believed to be particularly high.

The danger does not end there. Plastics also act as carriers of harmful chemicals, transporting pollutants into the digestive systems of marine animals. These toxic substances can interfere with reproduction, weaken immunity, and disrupt normal biological functions. Studies have also found that microplastics can accumulate in blubber, the liver, the lungs, and other vital organs, making them not just an environmental pollutant but a serious and growing biological threat.

What about sea turtles, seabirds, and other marine animals? Let us explore that next Saturday. Till then, have a wonderful Easter weekend!

(The writer is an environmentalist. Views personal.)