Microplastics have a significant impact on plankton, which are the foundational components of the marine food chain.
Here’s a detailed look at how microplastics affect those tiny organisms and lead to broader implications for the marine ecosystem.
What is Plankton in the First Place?
The Greek word "Plankton" means "drifter" or "wanderer". Plankton are tiny organisms that cannot actively swim against the current. They drift around and are carried by the tides and currents. Most plankton are microscopically small, but they can be up to a few inches in size.
There are two main categories of plankton, zooplankton (animals) and phytoplankton (plants).
Phytoplankton
Phytoplankton are microscopic plants like algae or cyanobacteria (tiny bacteria that photosynthesize) that are mainly found near the water's surface. There, they perform photosynthesis to convert sunlight into energy, just how you know it from regular plants. Doing so, they take in CO2 and create oxygen.
Zooplankton
Zooplankton are small animals like krill, tiny jellyfish, copepods (think of it like a microscopic shrimp), or the young of larger animals. Zooplankton mostly eat phytoplankton and are eaten by larger animals like humpback whales.
Ingestion of Microplastics by Plankton
Plankton, including both phytoplankton and zooplankton, are vulnerable to microplastic ingestion.
Zooplankton: These tiny crustaceans use filter feeding to capture their prey, which makes them prone to ingesting microplastics that are similar in size to their natural food sources.
Studies have shown that zooplankton like krill and copepods ingest microplastics, with krill being more likely to consume larger plastic particles. For example, one study found microplastics in 1 in every 34 copepods and 1 in every 17 krill in the waters of British Columbia. Phytoplankton: While phytoplankton do not actively ingest microplastics, exposure to high concentrations of microplastics can alter their photosynthetic rates and overall health.
This can reduce their growth and productivity, which in turn affects the entire food chain.
Ecosystem Impacts
The ingestion of microplastics by plankton has several ecosystem-level consequences:
Nutritional Impacts: Microplastics are nutrition-less by-products that fill up space in the digestive system of zooplankton without adding energy. This can lead to a decrease in the energy available to zooplankton, affecting their growth, reproduction, and overall health.
Biogeochemical Cycles: The consumption of microplastics by zooplankton can disrupt so called biogeochemical cycles, particularly the biological carbon pump. This process involves phytoplankton absorbing CO2 from the atmosphere, which is then stored in the deep ocean when these organisms sink. Microplastic ingestion can alter this process, leading to a decreased ability of the ocean to store carbon.
Food Chain Effects: Microplastics ingested by plankton can be transferred up the food chain, affecting larger marine species. This bioaccumulation of microplastics and associated toxins can have knock-on effects on marine biodiversity and the entire food chain, impacting the health and reproduction of various marine organisms.
Once microplastics find their way up the food chain, there is a good chance that they end up on our plates and in our bodies.
Ocean Deoxygenation: The ingestion of microplastics by zooplankton can contribute to ocean deoxygenation. In other words, the microplastics are depriving plankton and oceans of oxygen. This trend is exacerbated by global warming and a change in the oceans' temperature layers (stratification). This deoxygenation can have significant regional and global impacts on marine ecosystems.
Conclusion
The ingestion of microplastics by plankton is a critical issue that affects the foundation of marine food chains. Understanding these impacts is essential for managing and mitigating the effects of microplastic pollution on marine biodiversity and global biogeochemical cycles. Ongoing research aims to elucidate the full extent of these effects and to develop strategies for reducing microplastic pollution in the environment.
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