Marine Microplastics and Zooplankton
How marine microplastics are disrupting the planet's most abundant animals, zooplankton, and the systems they support.
What does every landscape on the planet have in common? From the highest peaks to the uninhabitable deserts to the deepest depths of the ocean, and everywhere in between, plastic pollution is present.
I am consumed by plastic pollution. My recent blog, Plastic Pollution and Coral Reefs, introduced zooplankton as an unintentional carrier of microplastics into the marine reef ecosystem. In this blog, we explore how microplastic vis-a-vis zooplankton upsets the homeostasis of our oceans.
What is Zooplankton?
Zooplankton are the most abundant animals on the planet. Zooplankton play a vital role in the marine food system and in regulating the Earth’s climate; aquatic superheroes. Zooplankton are tiny animals like krill and copepods, and immature stages of larger animals like baby crabs and fish. Zooplankton feed on microscopic plant-like organisms called phytoplankton, which get their energy from the sun.
Microplastics
Microplastics (<5mm in size) are found everywhere in our oceans and include particles and fibres of various shapes, sizes, colors, and materials. Microplastics come from two main sources. The first are nurdles or mermaid tears. These small plastic pellets are the raw materials used to manufacture plastic goods. The second are derived from the breakdown of larger plastic litter through exposure to sun and erosion, or they are released into wastewater when we wash nylon or polyester clothing. Researchers believe there could be as many as 125 trillion pieces of microplastic floating in the oceans; this number is growing.
The story of microplastics gets worse. As microplastics move through natural systems like the ocean they encounter environmental pollutants that attach to their surface. Microplastics act as a kind of magnet for the pollutants, concentrating them on its surfaces. When non-organic plastic and the organic pollutant converge, the toxicity of the pollutant is compounded. This toxicity threatens the marine environment and ultimately human health.
Microplastic and Zooplankton
Plankton are aquatic organisms that are unable to swim effectively against currents. There are two main types of plankton, phytoplankton which are plants and zooplankton which are animals. Both phytoplankton and zooplankton drift or are carried along by currents in the ocean. Zooplankton feed on phytoplankton then become food for animals up the food chain.
Zooplankton are filter feeders. Filter feeders lack complex digestive systems and feed through filtering large quantities of water; filter feeders come in all shapes and sizes, from tiny zooplankton to the largest animal on the planet, the blue whale. The filter feeder's natural diet is phytoplankton. Inevitably they ingest microplastics of similar size to phytoplankton. Microplastics impair natural digestion, for zooplankton, this means they don’t get sufficient nutrients which inhibits their development and reproduction.
This fact by itself is troubling news; recall that zooplankton are integral to the larger marine food system and climate regulation.
Zooplankton and the Marine Food Web
Disruption of both phytoplankton and zooplankton impedes the larger marine food chain. Microplastics then affect fish, sea birds, jellyfish, coral, marine mammals, and apex predators such as killer whales, great white sharks, and leopard seals.
Fish that ingest zooplankton at high levels and we’ve seen that most fish do are ingesting dangerous toxins that build up in their systems (think mercury in tuna, PCBs in freshwater fish). These toxins negatively impact growth, health, and reproduction. The ingestion of toxic chemicals and microplastics by predators means that eventually these plastics and chemicals that we have dumped into our environment will come full circle by making their way to our dinner plates!
Zooplankton and Ocean Carbon Sequestration
Aside from being an integral part of the marine food chain zooplankton also play a critical role in what is known as carbon cycling through photosynthesis. When zooplankton eat carbon-rich phytoplankton, their excrement naturally sinks to the bottom ocean floor. When the excrement contains microplastics it floats and rereleases carbon back into the atmosphere as CO2.
What Can We Do?
The story of zooplankton is a tragic reminder of how interconnected all life on earth is and illustrates that microplastics persist; they don’t degrade, they simply cycle through each new system impeding the natural food train.
Almost half the plastic made is single-use plastic, designed to be used once and thrown away. Together, we individuals can make a huge difference. With over 8 Billion people on the planet, imagine every person reducing single-use plastic by one item per day; that’s 56 Billion fewer pieces of plastic per week entering the environment.
Small Actions Create Big Impact
Five simple ways to achieve this:
- Use a refillable water bottle.
- Refuse single-use plastic water bottles from hotels, stores, and restaurants. Request instead that they create water refill stations.
- Use a reusable coffee cup. Some shops extend discounts for using your own cup.
- Don’t let trash reach our waterways. When you see trash on the street, trail, or beach, pick it up!
- Inspire change by sharing what you learn with family and friends.
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