Microplastics Pose Risk to Ocean Plankton, Climate, Other Key Earth Systems
Claire Asher | October 9, 2023 | Mongabay
Heart-wrenching images of sea turtles entangled in fishing nets, or dead seabirds with stomachs clogged by plastic trash, justifiably attract media and public attention. But zoom down to the microscopic scale and plastics are having far more pervasive, insidious effects on ocean life — even potentially impacting key Earth operating systems that keep the planet habitable.
An estimated 12 million metric tons of plastic currently enters the ocean each year. This plastic debris gradually breaks down into smaller and smaller fragments — micro- and nanoplastics — which, while less visually striking, can have serious effects on marine ecosystems and may even pose a threat to the stability of Earth’s climate.
A recent estimate suggests that as much as 358 trillion microplastic particles are floating on the surface of the world’s oceans, with untold trillions more in deeper reaches. Their prevalence is particularly worrisome because these tiny particles are easily mistaken as food by marine life. The smaller the microplastic particles, the more species that can ingest them, from huge filter-feeding whales to tiny organisms at the base of the food chain collectively known as plankton.
“Microplastics truly are omnipresent in these environments,” says Carroll Muffett, president and CEO of the Center for International Environmental Law, adding that “they are affecting marine biota at every trophic scale.”
Unlike larger plastic litter, which can entangle and suffocate marine animals, microplastics are unlikely to be lethal over short time scales. But their long-term impacts on plankton and microbial communities could have profound implications for marine biodiversity and even hinder carbon storage and nitrogen cycling in the world’s oceans.
Plastic pollution pushes Earth out of ‘safe zone’
Plastics, along with other synthetic chemicals and pollutants dubbed “novel entities” by scientists, are considered a threat to the stability of Earth’s operating system because of their persistence in the environment and potential toxicity to humans and wildlife —with the harm done to biodiversity in turn altering life-giving geophysical processes.
The production and release of vast amounts of plastic into marine ecosystems is now being recognized as a key potential threat to environmental stability as defined by the Planetary Boundaries framework. That theory attempts to quantify nine Earth system thresholds that humanity cannot transgress without risking life as we know it.
Researchers suggest we have already exceeded the safe threshold for novel entity chemical pollution.
Plastics are also pushing us further into the danger zone for other planetary boundaries, especially the loss of biosphere integrity and function, through their lethal and sublethal effects on living organisms. Research is also showing that plastics, via their impact on microscopic ocean life, may have knock-on effects, destabilizing three other critical boundaries, including ocean acidification, climate change and biogeochemical flows of nitrogen.
The smallest plastic particles “are likely the ones that pose the biggest planetary boundary threats,” says Meredith Seeley, a postdoctoral researcher studying marine microplastics at the National Institute of Standards and Technology in Maryland, U.S.
Microplastics ‘clogging’ ocean’s living carbon pump?
The connection between plastic pollution and Earth’s climate hinges on the critical role tiny marine organisms play in storing carbon in the ocean. Earth’s oceans are the largest natural carbon store, making them crucial to mitigating increases in atmospheric CO2. This carbon-storing function occurs in two steps: First, CO2 in the atmosphere dissolves in seawater at the ocean’s surface. Then, plankton take up that carbon and eventually store it in the deep ocean. The latter process is known as the biological carbon pump.
Plankton is a catch-all term for a diverse array of tiny organisms that float in vast numbers on ocean currents. They come in two main types: Phytoplankton (algae and cyanobacteria that use photosynthesis to harvest solar energy) and zooplankton (the small animals that feed on phytoplankton).
Research shows that exposure to microplastics in high enough concentrations can alter photosynthesis in phytoplankton and reduce feeding rates in zooplankton. Studies have also linked consumption of microplastics by these organisms to reduced growth, lifespan, reproduction and fertility across a range of plankton species. Those impacts can have knock-on effects all the way up the food chain.
