Toxic ocean pollution adds to fish woes

The oceans are dying. Humans are to blame but we know precious little about the where, why and how. More is known about the moon than about the inky-black world deep below the surface.

That is changing, slowly, as robotic submarines probe areas such as the 11km-deep Mariana Trench in the Pacific Ocean. The intense pressure means that nothing else can go that deep without being crushed, except the tiny, fluorescent, animals that thrive in the darkness.

What the submarines are finding – thanks to sampling and images which record a fraction of the ocean – is starting to piece together a map of the oceans. In the latest such expedition, a team of researchers from the Institute of Biological and Environmental Sciences at the University of Aberdeen found “extraordinary levels of pollutants” on the ocean floor.

The research, “Bioaccumulation of persistent organic pollutants in the deepest ocean fauna,” was published in the journal Nature Ecology and Evolution in late February. It found toxic chemicals that banned in the 1970s had found their way into the ocean and were accumulating in fish and other creatures.

Some 1.3-million tonnes of these chemicals, known as persistent organic pollutants, were produced between the 1930s and 1970s. These were mainly used to control crop pesticides. They were banned when it became clear that they were potent endocrine disruptors, which distorts genetic codes, creating birth defects in humans and animals.

About 65% of the disruptors have ended up in landfills, while 35% are to be found in the world’s oceans. They do not break down and are water-repellent, so stick to plastic waste floating across the oceans.

One massive concentration of plastic – the so-called Great Pacific Garbage Patch – has collected above the Mariana Trench. This is where the Aberdeen university team sent their robot submarine to take samples and record video.

Like similar expeditions, it found evidence of tinned food and plastic waste on the ocean floor. Much of this comes from waste from coastal settlements and vessels, but the team also said that when plastic in the garbage patch degrades, it sinks to the ocean floor. Hungry crustaceans and other animals then jump at the opportunity to eat the new food.

The organic pollutants then accumulate in the animals, with the researchers warning that the problem is “pervasive across the world’s oceans”.

Similar research, published in the journal Elementa at the same time, found that this sort of pollution – and the changing climate – would threaten the survival of ocean animals this century.

The research – “Major impacts of climate change on deep-sea benthic ecosystems” – said that the amount of food available for fish and other creatures in the oceans would decrease by up to 55% this century. This would starve animals, which are already struggling to adapt to warming oceans, with less oxygen content and increasing acidity.

The researchers, from the Centre for Earth and Marine Science and Technology at the Heriot-Watt University in Edinburgh, said that by the end of this century, oxygen levels in the ocean would decrease by 3.7%. This would threaten the ability of ocean creatures to survive, given that they have evolved to survive in a very specific set of conditions.

With even more intrusion into ocean ecosystems expected – thanks to increased oil and gas drilling, fishing and mining – the team said the impact would be profound. This is a biome that gives the world its biggest single source of proteins and supports the livelihoods of millions of people.

Humans might just destroy the last part of the Earth that we know little about, before we can learn more. The consequences for the billions of people that rely on the oceans could be devastating.

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Sipho Kings
Sipho Kings is the acting editor-in-chief of the Mail & Guardian

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