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  • The Ocean's Silent Killer: Microplastics Devastate Marine Ecosystems

The Ocean's Silent Killer: Microplastics Devastate Marine Ecosystems

The impact of microplastics extends globally, with profound effects on marine ecosystems. A year-long investigation published in Microplastics & Nanoplastics provided compelling evidence of microplastics descending into the abyssal depths of the North Atlantic Ocean, often embedded within marine snow, challenging previous assumptions that plastics remain near the surface. Scientists have also detected nanoplastics (1,000 times smaller than microplastics) at all sampled depths in the North Atlantic, with an estimated 27 million metric tons present, indicating widespread contamination that could interfere with the ocean's natural carbon capture processes.

In the upper ocean, microplastics wreak havoc on marine life. They significantly affect ocean plants like phytoplankton, altering photosynthesis and hindering growth, with cascading effects throughout the food web. Marine animals, from microscopic zooplankton to large whales, ingest microplastics, leading to physical blockages, reduced nutrient absorption, and starvation. Microplastics also act as vectors for pathogens, spreading infectious diseases and increasing the severity and mortality rates of viral fish diseases by damaging delicate tissues. Commercial fishing, ironically, is both a source of (lost gear, wear and tear) and a victim of microplastic pollution, with consequences for fish health, reproductive capabilities, and ultimately, human seafood consumption.

Impact on Ocean Plants

Microplastics significantly affect ocean plants, particularly phytoplankton, which form the base of the marine food web. Exposure to microplastics in sufficient concentrations can alter the process of photosynthesis in phytoplankton and hinder their growth, lifespan, reproduction, and fertility. These disruptions can have far-reaching consequences throughout the food chain. Phytoplankton and zooplankton are crucial for the biological carbon pump, a primary mechanism by which oceans store carbon, and microplastics may impede this process. Microplastics in marine sediments can also alter microbial communities and disrupt nitrogen cycling, potentially intensifying harmful algal blooms. Furthermore, changes in plankton communities due to microplastics can worsen ocean deoxygenation, starving marine organisms of vital oxygen. Some aquatic plants, such as seagrasses, have shown an ability to act as natural sinks for microplastics, collecting them from the water and depositing them into the sediment.

Impact on Marine Animals and Mortality Rates

The ingestion of microplastics is a widespread problem across marine life, from microscopic zooplankton to large filter-feeders like whales. Animals often mistake these tiny plastic fragments for food due to their size and appearance. Once ingested, microplastics can accumulate in digestive systems, leading to physical blockages, a false sense of fullness, reduced nutrient absorption, impaired growth, and starvation. Beyond physical obstruction, microplastics can carry and release harmful chemicals, including those added during plastic production, which can cause developmental problems, issues with reproduction, altered behavior patterns, and a diminished ability to fight off diseases.

While direct short-term lethality from microplastics may not always occur, their long-term effects on plankton and microbial communities can have profound implications for marine biodiversity. However, in some laboratory studies, high concentrations of mixed microplastic blends have resulted in significant mortality rates in species like copepods. Larger plastic debris (which breaks down into microplastics) is estimated to cause the deaths of over a million seabirds and more than 100,000 marine mammals annually through entanglement and suffocation. The bioaccumulation of microplastics and associated toxins up the food chain also poses significant health risks to top predators, including humans who consume seafood.

Microplastics and Commercial Fishing

The commercial fishing industry is both a contributor to and a victim of microplastic pollution. Fishing gear, often made from durable plastics, can be lost at sea and eventually break down into microplastic and nanoplastic particles that are then ingested by marine organisms. Normal commercial fishing activities, through the wear and tear of ropes and gear dragged along the seafloor, are also a source of microplastics, with estimates suggesting thousands of tons produced globally each year from this source alone.

The presence of microplastics in the marine environment has direct implications for commercial fisheries. Microplastics can impair the health and reproductive capabilities of many fish species, which can lead to declines in fisheries productivity. Studies have found microplastics in a high percentage of commercially important fish, including in their gills, digestive tracts, and even edible organs like the liver. The transfer of microplastic-associated contaminants to seafood also raises concerns about potential impacts on human health through consumption.

Microplastics and Pathogenic Illnesses

Microplastics can exacerbate pathogenic illnesses in marine life in several ways. They can act as vectors, attracting and carrying pollutants and various pathogens, including land-based parasites, and transporting them across marine environments. This can lead to the spread of diseases to new areas and to filter-feeding animals like shellfish, increasing the risk of infection for both wildlife and humans who consume contaminated seafood.

Laboratory studies have demonstrated that exposure to microplastics can increase the severity and mortality rates of viral fish diseases. For instance, in rainbow trout, exposure to microplastics, particularly nylon fibers, significantly increased their susceptibility and death rates when subsequently exposed to infectious hematopoietic necrosis virus (IHNV). Researchers suggest that microplastics can damage the delicate tissues of fish gills and gut lining, creating entry points for viruses and triggering inflammatory responses that hinder the fish's ability to fight off infections. These findings have significant implications for aquaculture, where fish are often in environments with both high pathogen and microplastic concentrations, and potentially for wild fish populations as well.

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