Coral reefs, often called the “rainforests of the sea,” are complex underwater ecosystems that house a significant portion of marine biodiversity. They provide shelter and food for a variety of ocean life, supporting approximately 25% of all marine species despite covering less than 1% of the ocean floor.
These vibrant natural structures also offer benefits to humans by supporting fisheries, protecting coastlines from storms, and contributing to medical research. However, these ecosystems face numerous threats, with plastic pollution presenting a significant danger. An estimated 75 to 199 million tons of plastic waste currently exist in the oceans, with billions of pounds more entering the marine environment annually.
Direct Physical Harm
Plastic debris directly harms coral reefs through various physical interactions. Larger plastic items, such as fishing nets and bags, can entangle corals, restricting their natural growth and causing breakage. This entanglement can lead to tissue damage and detachment of coral fragments from the reef structure.
As plastic moves with ocean currents, it can rub against coral structures, leading to abrasion. This continuous scraping creates physical wounds and tissue loss on the corals. These open wounds make corals more susceptible to infection.
Plastic items can also settle on corals, smothering them by blocking sunlight and water flow. This suffocation impedes photosynthesis and can create low-oxygen conditions that lead to coral death. Researchers have observed plastic debris covering 92% of surveyed reefs, including remote areas.
Chemical Leaching and Microplastic Ingestion
Beyond physical damage, plastics introduce chemical pollutants into the reef environment. As plastics degrade, they release harmful chemicals, including bisphenol A (BPA) and phthalates, into the surrounding seawater. These substances can disrupt the hormonal processes of marine life, potentially impairing coral reproduction and growth rates. Chemicals leached from plastics can also accumulate in coral tissues, causing stress and harm.
Corals, as filter feeders, can inadvertently ingest microplastics, which are tiny plastic fragments. Studies have shown corals ingest microplastics at rates comparable to plankton, their natural food source. This ingestion can lead to false satiety, reducing the coral’s intake of food and leading to stunted growth and weakened health.
Microplastics can also carry adsorbed toxins from the seawater due to their porous surfaces. When ingested, these toxic pollutants can accumulate in coral tissues. The presence of microplastics can also increase the energy demands of corals, as they expend energy to process these indigestible particles.
Disease Vulnerability and Ecosystem Consequences
Plastic debris can serve as a vector for disease-causing microorganisms, increasing coral susceptibility to illness. The rough surfaces of microplastics can promote the colonization of harmful microbes, which are then transported to corals upon contact. Physical injuries caused by plastic, such as cuts and abrasions, create entry points for these pathogens.
Research indicates a significant increase in disease prevalence when corals are in contact with plastic. One study found that the likelihood of disease increased from 4% in plastic-free reefs to 89% in the presence of plastic debris. Specific diseases like skeletal eroding band disease, white syndromes, and black band disease are more common in corals exposed to plastic.
The degradation of corals due to plastic pollution has cascading effects throughout the entire reef ecosystem. Corals provide habitat, shelter, and breeding grounds for many marine species. As corals decline, the loss of this complex three-dimensional structure leads to a reduction in habitat for fish and invertebrates. This can disrupt marine food webs, decrease fish populations, and lead to an overall decline in biodiversity. Coral reefs also offer coastal protection by reducing wave energy, and their decline can increase shoreline erosion.