Marine Atlas: Maximizing Benefits for Tonga

PLASTIC OCEAN: MICROPLASTICS CONCENTRATION Like the rest of the world’s oceans, Tonga’s waters are overflowing with plastic. Only 5 per cent of plastics are recy- cled effectively and forecasts expect that by 2050 there will be more plastic than fish in the world’s ocean.

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MICROPLASTICS CONCENTRATION grams / km 2

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1,000 - 2,500 2,500 - 5,000 5,000 - 10,000 10,000 - 20,000

North Paci c Gyre

Surface Currents

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Copyright © MACBIO Map produced by GRID-Arendal Sources : Becker et al, 2009; Claus et al, 2016; Van Sebille et al, 2015; Smith and Sandwell, 1997.

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TONGA

South Paci c Gyre

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the ocean surface (see the map) is not necessari- ly good news.

The world produces 300 million tons of plastic each year. About 2 per cent of it—around 8 million metric tons—ends up in the ocean. It is a stag- gering amount, yet only 1 per cent of this plastic is actually found on the surface of the ocean. Half of this 1 per cent becomes caught in large gyres (see map); the other half is more widely dispersed. The other 99 per cent (7.92 million metric tons) of plastics in the ocean worldwide are unaccounted for each year. Science has only just begun to unravel the riddle of where this unaccounted-for plastic ends up. At the turn of the millennium, scientists uncovered a previously unknown phenomenon: microplastic. Eighty per cent of plastic waste enters the ocean via rivers and the other 20 per cent is tossed over- board from ships (see graphic). A portion of the plastic waste is carried great distances by ocean currents and gathers in large trash vortices such as the Great Pacific Garbage Patch in the North Pacific Gyre. On this journey, which can take up to 10 years, large pieces of plastic are progressively eroded, broken down by sunlight and eaten by bacteria, fragmenting into many smaller pieces. The result is microplastic—plastic particles that are smaller than 5 millimetres.

agine. Large bits of plastic are relatively rare, and one could actually swim through a gyre without noticing the microplastic that composes it. The remaining 99 per cent of the waste that begins its journey on the coasts never reaches garbage patches. It also breaks down into microplastic and disperses through the ocean, before finally sinking into the depths. In fact, the plastic con- centration on the ocean floor is 1,000 times great- er than on the surface. In light of this, Tonga’s comparably low concentration of microplastic at As we know, the second deepest part of the world’s oceans is the bottom of the Tonga Trench. You wouldn’t expect to find signs of civilization at this depth, would you? Yet just as plastics and other types of pollution are affecting the shallow waters of the marine environment, so they are the deepest marine trenches. In March 2017, scientists discov- ered a container of Spam at 4,947 metres on the slopes of a canyon leading to the Sirena Deep in the Mariana Trench. This is symbolic of how pollution can penetrate even the deepest marine environments, such as the Tonga Trench. (The Guardian, 2017) Litter in the deep

The microplastic is trapped on the ocean floor, embedded in the sediment. It is gradually forming a new geological layer, the “plastic horizon”, which researchers of the future will attribute to our era. The sad truth is that we use the deep sea as a gigantic dustbin and benefit from the fact that the majority of the waste seemingly disappears forev- er, rather than washing up at our feet again. While the portion of microplastic that remains afloat may seem small, it is the cause of a large problem with far-reaching effects. It is no wonder that fish mistake microplastic for plankton and eat it, since there is six times as much plastic as plankton in some parts of the ocean. Very small pieces of plastic can penetrate the fish’s intestinal walls and become trapped in the surrounding tissue. The mi- croplastic then enters the food chain and eventually winds up on our plates and in our own stomachs. The consequences of consuming microplastic have yet to be studied—after all, microplastic itself has only been a research topic since 2007. One finding is already cause for concern: the surface of mi- croplastic acts like a sponge that soaks up toxins, including environmental poisons such as PCB and disease-causing germs, helping them spread and threatening entire fish populations.

Thus, the Great Pacific Garbage Patch is not the massive islands of trash that one might first im-

THREATS MAXIMIZING BENEFITS FOR TONGA

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