Intermediate 10 minutes
Marine pollution: what reaches the sea and doesn't leave
Plastics, microplastics, oil, wastewater, and invisible chemistry
Everything that gets thrown away ends up somewhere, and on a planet covered in water, that somewhere is usually the sea. The difference from waste on land is that here nobody sees it, it bothers no one, and it doesn't smell. Until it turns up inside a fish.
In this article you'll see the main forms of marine pollution (plastics and their fragmentation, oil, wastewater, and chemical pollutants) how they reach the sea, what effects they produce at different levels of the food chain, and what a diver can do about it.
Unlike climate change, a large part of pollution is a local problem with local solutions, and it's the area where individual action and dive communities have a measurable effect.
Plastics: the waste that doesn't disappear
Plastic reaches the sea mostly from land, carried by rivers, runoff, and wind, and the rest comes directly from maritime activity: lost fishing gear, vessel waste, and discharges. Annual input is measured in millions of tons.
Plastic doesn't biodegrade in the usual sense: it fragments. Sunlight, wave action, and abrasion break it into progressively smaller pieces without changing its chemical nature, and that process continues indefinitely down to microscopic scales.
The direct effects of large fragments are of two kinds. Entanglement, which mainly affects turtles, marine mammals, and birds, and for which abandoned nets and lines are the main culprits: they keep fishing for years, and they're the ghost nets already covered in the article on environmental accidents.
And ingestion: animals that mistake bags for jellyfish, fragments for prey, or caps for food, and that accumulate indigestible material that takes up space in the digestive tract without providing anything. This is extensively documented in seabirds and turtles.
There's a less obvious effect that worries reef ecologists: contact between plastic waste and coral colonies is associated with a higher incidence of disease, likely due to abrasion and the transport of pathogens.
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