Invisible plastics are changing our oceans [Commentary]

Every year, when summer rises to a boil, most of India waits in anticipation of the rains. In Mumbai, where I grew up, monsoons are inseparable from the fury of the ocean. Waves rise with such force that they break on the streets, drenching unfortunate children who forget to close their school bus windows. These waves also bring huge quantities of plastic trash to the shores of the Western coast — a reminder of how much plastic waste has inundated marine environments. While the crisis of visible plastic waste has received widespread attention, there’s growing concern about its smaller counterpart — microplastics — and how these tiny particles are threatening the foundations of marine life in India and the world.

Last year, India emerged as the world’s biggest plastic polluter, contributing a fifth of global plastic waste. Poor waste collection practices and uncontrolled landfills allow plastics to leach out into the environment, across both urban and rural areas. Many of these plastics wash out into waterways and eventually the ocean, especially during the monsoon. When these plastics are exposed to the elements, they break down into small particles called secondary microplastics (<5 millimetres). Primary microplastics, on the other hand, are already produced at this small size — for example, microfibres in synthetic clothing or microbeads in personal care products like facewash and toothpaste. While not yet fully understood, research suggests that these tiny particles negatively impact a wide variety of marine species. It’s worth paying special attention to how microplastics affect keystone species — like mangroves, coral, and seagrass — that form the basis of marine habitats in India. These species and the ecosystems they create support millions of different organisms, including human beings.

Playing rough: The physical toll

Scientists have noted that there is a lower concentration of microplastics in seawater as compared to the amount of plastics entering the ocean, suggesting that certain habitats act as a sink for microplastics. These small particles are easily trapped in dense areas like seagrass meadows and mangrove forests — causing them to become ubiquitous in these environments. Similarly, reef-building corals have been shown to store microplastics in their skeletons as they grow. While this can help reduce the concentration of microplastics in the ocean, with some researchers even citing mangrove plantations as a way to curb marine pollution, there is a need to look deeper into how this can impact the organisms themselves.

The accumulation of plastics — along with the chemical additives used in their production — can affect the health of these species and their dependent ecosystems. Microplastics have hard, irregular surfaces that tend to rub against stationery plants and animals when they are present in large quantities in the water column. This increases the risk of abrasion, which can cause physical damage to seagrass blades, delicate tissues of corals, and young mangrove seedlings. Sustained abrasions make these creatures a target of bacterial and other infections, reducing their immunity.

Plastics also tend to get caught and concentrated in structurally complex habitats. For example, blades of seagrass host small stationary plants, like diatoms and macroalgae, called epiphytes. These epiphytes often trap and grow over passing microplastics, sealing them to the blade’s surface. Small particles also get trapped in the sediments that seagrass grows from, due to the naturally turbulent movement of water close to the seabed that plays a role in trapping sediment. These microplastics reduce the ability of micro-organisms living in the sediment to perform key functions like nitrogen fixation and nutrient cycling. Research shows that plastic’s adhesive properties cause it to stick to leaves, rhizomes, and roots, which can reduce photosynthesis — a phenomenon that has been observed in both mangrove and seagrass ecosystems. Certain plastic additives like bisphenol A, which have been linked to health issues in people, may also reduce chlorophyll production in the long-term.

Sticky situation: The rise of the plastisphere

The ocean is a colossal place, where small particles can travel vast distances. Due to their textured, hydrophobic surfaces, microplastics offer a ride to a variety of other compounds and small creatures. These include microbes like bacteria and fungi, environmental pollutants like heavy metals and organic chemicals, antibiotics, and more. In fact, invasive species of barnacles have been found hitching onto marine plastic debris off the coast of Qatar. Microplastics have also been found to spread and extend the lifespan of antibiotic-resistant bacteria and fungi, in both marine and freshwater ecosystems. According to one study, over 50% of microplastics collected off the coast of Maharashtra had been colonised by microbial organisms, rising to 66% in Mumbai’s famous Girgaon Chowpatty beach.

Since microplastics can be mistakenly ingested by coral and other marine organisms, the plastisphere poses a significant risk in terms of their exposure to heavy metals, toxic chemicals, and a host of microbial organisms. This is compounded by issues like rising temperatures, which cause corals to bleach white by expelling the symbiotic algae, called zooxanthellae, that live within their polyps. Zooxanthellae are photosynthetic, providing corals with food in exchange for a secure habitat. When corals bleach, they lose this food source and need to eat more zooplankton from the water column — causing them to ingest more plastic in the process. While different coral species are affected differently by the presence of microplastics, many corals experience reduced energy, growth, and fertility. However, these differences also mean that microplastics can influence the community structure of coral reefs, depending on which species are most and least affected by their presence.

Why does this matter?

In the wild, microplastics are just one of many stressors — alongside rising temperatures, ocean acidification, and other kinds of pollution. While coral reefs, seagrass meadows, and mangrove forests are resilient ecosystems, the combination of all these threats together can jeopardise their health. Each of these organisms plays a critical role in habitat building — for example, coral reefs are home to 25% of all marine life. In India, seagrass meadows are home to around 1,250 different species; that number rises to over 4,000 in the case of mangroves. They also provide essential services like carbon capture and protection against storms and erosion. Significant damage to these ecosystems will have cascading impacts on people, who depend on them for livelihoods, nutrition, medicine, and more.

Additionally, microplastics have been observed moving up the food chain into a wide variety of aquatic animals including fish and fish-eating birds, crustaceans, molluscs, and zooplankton. Fish are especially affected, both by toxic chemicals used in plastic production and pollutants accumulated by the plastisphere. These chemicals can cause changes in their central nervous systems, which can alter swimming and reproductive behaviour. Chemical additives like phthalates are notable endocrine disruptors and can affect their reproductive systems and the growth of young fish. These plastics also accumulate in their bodies and are later consumed by humans, especially in the case of dried fish, which are eaten without removing the gut — a common practice in India. While the impacts of microplastics on the human body are not yet fully understood, increased exposure to these chemicals is a growing concern for issues like cancer, endocrine disruption, insulin resistance, and more.

The scale at which plastics are produced and discarded in today’s world is unprecedented — yet we have a limited understanding of their long-term effects on people and our planet. Most studies so far are laboratory-based and use higher concentrations than the amount of plastics in the ocean today, as future scenarios — so their influence in the wild is not fully understood. It’s especially concerning that microplastics have been found to disrupt key biological functions of organisms that form the basis of marine habitats — including photosynthesis, growth, and reproduction. There’s a pressing need to uncover what the accumulation of these particles and their associated chemicals means for human and planetary health, to drive faster and more urgent action on addressing the issue. As the next monsoon brings its waves of waste to our doorstep, we could pause to think about what it shows us — and about what lies invisible, right under the surface.

The author is a consultant for the River Bhima project at Society for Promoting Participative Ecosystem Management and a consultant at India Climate Collaborative.

Read more: [Explainer] Living with microplastics, is not fantastic

Banner image: Microplastics are accumulating in crucial marine ecosystems where they cause physical damage and disrupt essential biological processes. Image by Emina Mamaca via Wikimedia Commons (CC BY-SA 4.0).