On June 8, humans dumped 13,000–15,000 pieces of plastic into the ocean. At the same time, we were celebrating United Nations (UN) designated World Oceans Day, which raises awareness about oceans’ importance to humanity. It also connects people worldwide through social media, encourages participation in partner organizations, and inspires year-round action to protect and restore marine ecosystems.
Covering 71 per cent of the planet’s surface, oceans are a major source of food and medicine, provide most of the world’s oxygen, and act as a sink for carbon dioxide. World Oceans Day is a harsh reminder of the major threats posed by pollution, overfishing, climate change, and habitat destruction.
Annually, 13 million tonnes of plastic are dumped into the ocean, killing 100,000 marine animals that often die after tangling themselves in or ingesting plastic debris, leading to internal injuries and starvation. Plastics also introduce chemicals into the water and greenhouse gases into the air. These chemicals can remain intact for centuries or instead degrade into microplastics, which introduce toxins into the food chain.
Other man-made pollutants, such as chemical fertilizers, enter the food chain after small marine organisms consume them. Nitrogen-rich fertilizers result in massive algal blooms that rob the water of oxygen, creating ‘dead zones’ where only a few species can survive. Meanwhile, oil spills can poison animals and destroy the insulating capability of fur and the water repellency of feathers, causing mammals and birds to die of hypothermia. Noise pollution from ships disrupts the migration, communication, and reproductive patterns of whales, and it can even kill invertebrates like squid.
Over the past century, humans have depleted the majority of the planet’s fish stocks, leaving fewer fish and marine invertebrates to reproduce and sustain healthy populations that can withstand future fishing efforts. Size-selective fishing, often used as a conservation measure, lowers genetic diversity, while trawling along the seafloor can destroy fragile environments. Additionally, millions of animals not targeted by fishermen—referred to as bycatch—are caught, though technologies that exclude non-target species are now required in some areas. Aquaculture, the world’s largest-growing food industry, comes with problems of its own but is increasingly viewed as a sustainable alternative to fishing for many species.
Arguably, the biggest threat to the oceans is climate change. Aside from sea level rise, global warming is making oceans hotter, reducing oxygen levels, and forcing species to relocate to new areas. Furthermore, extreme and unpredictable weather associated with climate change can damage coral reefs and other coastal ecosystems.
A striking effect of this ocean warming is coral bleaching, a stress response to environmental changes that has become more common in recent years. When under stress, algae leaves the coral, causing it to turn white and making it more vulnerable to future pressure. Coral is also bleached by acidification, the result of large quantities of carbon dioxide dissolving in oceans, which makes water more acidic and threatens the growth and survival of organisms with calcium carbonate skeletons and shells, such as corals and shellfish.
Coastal and marine habitats are home to a wide range of organisms and are essential for the overall function of ecosystems. Coastal development and aquaculture can destroy vital habitats and fish nurseries, such as estuaries and mangroves, while destructive fishing techniques like deep-sea trawling scrap entire habitats from seamounts and underwater mountain ranges. Pollution, tourism, and climate change also destroy marine habitats.
While World Oceans Day is a reminder that humans are dangerously threatening the marine environment, all is not lost: Through education and global coordination, the event inspires the development of new and ongoing solutions to mitigate humans’ impact on the earth.