The Great Pacific Garbage Patch

In news– In a recent study, researchers from Canada, the Netherlands, and the U.S. have reported that coastal lifeforms have colonised plastic items in the Great Pacific Garbage Patch, throwing up many dubious firsts.

Key findings-

The tsunami off the Japanese coast in 2011 contributed to the debris in this garbage patch.
Until at least 2017, researchers had found debris washing ashore on the West coast of North America containing live lifeforms originally found in Japan.
From November 2018 to January 2019, researchers collected 105 pieces of plastic debris from the eastern part of the North Pacific Subtropical Gyre (NPSG), the most heavily plastic-polluted ocean gyre on the globe.
Based on studying them, they reported that 98% of the debris items had invertebrate organisms.
They also found that pelagic species (i.e. of the open ocean) were present on 94.3% of them and coastal species, on 70.5%. That is, organisms found on coasts were getting by on small floating islands of garbage (to humans) out in the Pacific Ocean.
The number of coastal species such as arthropods and molluscs identified rafting on plastic was over three-times greater than that of pelagic species that normally live in the open ocean.
In all, they found organisms belonging to 46 taxa, and 37 of them were coastal; the rest were pelagic.
Among both coastal and pelagic organisms, crustaceans were the most common.
The coastal species were most commonly found on fishing nets whereas the pelagic species, on crates.
According to the paper, “Nearly all taxa were of Northwest Pacific origin”, including Japan.
Similarly, most debris items (85.7%) did not have identifiable markings linked to origin, such as manufacture locations or company/brand names.
However, eight of the remainder were from East Asia and five specifically from Japan. Four items were from North America.
The researchers also found that 68% of the coastal taxa and 33% of the pelagic taxa reproduced asexually, and that there was evidence of sexual reproduction among the hydroids and the crustaceans, among others. They found a strong positive correlation between reproduction and mobility.

What is the Great Pacific Garbage Patch?

There are some water currents in the oceans that, driven by winds and the Coriolis force, form loops. These are called gyres.
The North Pacific Subtropical Gyre (NPSG) is one such, located just north of the equator in the Pacific Ocean.
It consists of the Kuroshio, North Pacific, California, and North Equatorial currents and moves in a clockwise direction.
These currents flow adjacent to 51 Pacific Rim countries. Any trash that enters one of these currents, from any of these countries, could become part of the gyre.
Inside this gyre, just north of Hawai’i, lies a long east-west strip where some of the debris in these currents has collected over the years.
The eastern part of this is the Great Pacific Garbage Patch. It is, as per one estimate, 1.6 million sq. km big and more than 50 years old.
The patch contains an estimated 45,000-1,29,000 metric tonnes of plastic, predominantly in the form of microplastics.
The numerical density of plastics here is around 4 particles per cubic metre.
Mass-wise, however, heavier, more visible objects that haven’t yet broken down into smaller particles accounted for 92% in 2018.