The Kritic

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A white fleck of plastic is engulfed by a coral polyp.Source: Alex Seymour, Duke Univ.

Scientists have long known that marine animals mistakenly eat plastic debris because the tiny bits of floating plastic might look like prey. But a new Duke University study of plastic ingestion by corals suggests there may be an additional reason for the potentially harmful behaviour. Visual cues, such as a resemblance to prey, don’t factor into the appeal, the researchers noted, because corals have no eyes.

This new study suggests there may be an additional reason for the potentially harmful behaviour: The plastic just plain tastes good.

“Corals in our experiments ate all types of plastics but preferred unfouled microplastics by a threefold difference over microplastics covered in bacteria”, said Austin S. Allen, a PhD student at Duke’s Nicholas School of the Environment. “This suggests the plastic itself contains something that makes it tasty.”

“When plastic comes from the factory, it has hundreds of chemical additives on it. Any one of these chemicals or a combination of them could be acting as a stimulant that makes plastic appealing to corals”, said Alexander C. Seymour, a geographic information systems analyst at Duke’s Marine Robotics and Remote Sensing Centre, who co-led the study with Allen.

Further research will be needed to identify the specific additives that make the plastic so tasty to corals and determine if the same chemicals act as feeding stimulants to other marine species.

Microplastics, tiny pieces of weathered plastic less than 5 millimetres in diameter, began accumulating in the oceans four decades ago and are now ubiquitous in the marine environment. They pose a major threat to foraging sea animals, including many species of birds, turtles, fish, marine mammals and invertebrates.

Because plastic is largely indigestible, it can lead to intestinal blockages, create a false sense of fullness or reduce energy reserves in animals that consume it. “About eight percent of the plastic that coral polyps in our study ingested was still stuck in their guts after 24 hours”, said Allen.

It can also leach hundreds of chemical compounds into their bodies and the surrounding environment. The biological effects of most of these compounds are still unknown, but some, such as phthalates, are confirmed environmental estrogens and androgens – hormones that affect sex determination.

Allen and Seymour conducted their two-part study using corals collected from waters off the North Carolina coast. In their first experiment, they offered small amounts of eight different types of microplastics to the corals to see if the animals would eat the bite-sized bits versus other similarly sized items offered to them, such as clean sand.

“We found that the corals ate all of the plastic types we offered and mostly ignored sand”, Allen said.

In the second experiment, they put groups of coral into separate feeding chambers. Each group was offered the same amount of “food” — weathered plastics — for a 30-minute period, but some groups got only particles of unfouled microplastics while others got only particles of weathered microplastics fouled with a bacterial biofilm. This experiment verified that the corals would eat both types of plastic, but preferred the clean type by a three-to-one margin.

The researchers hope their findings will encourage scientists to explore the role taste plays in determining why marine organisms ingest microplastics.

“Ultimately, the hope is that if we can manufacture plastic so it unintentionally tastes good to these animals, we might also be able to manufacture it so it intentionally tastes bad”, Seymour said. “That could significantly help reduce the threat these microplastics pose.”

Allen and Seymour’s peer-reviewed study was published October 23, 2017 in the online edition of journal Marine Pollution Bulletin. You can access the study free of charge until December 10, 2017 by clicking here.

Daniel Rittschof, Norman L. Christensen Professor of Environmental Sciences at Duke’s Nicholas School, co-authored the new paper. Funding for the research came from the Oak Foundation. Allen and Seymour both earned Master of Environmental Management degrees from the Nicholas School in 2016.

CITATION: “Chemoreception Drives Plastic Consumption in a Hard Coral,” Austin S. Allen, Alexander C. Seymour, Daniel Rittschof, Marine Pollution Bulletin, Oct. 23, 2017. DOI: 10.1016/j.marpolbul.2017.07.030

Harmful Plastics

Much of Australia’s waste plastic is ending up in the ocean, and in fish.Photo: John Schneider

Each square kilometre of Australian sea surface water is contaminated by around 4,000 pieces of tiny plastics, according to our study published today in journal PLOS ONE and data repository Dryad.

These small plastic fragments, mostly less than 5mm across, are loaded with pollutants that can negatively affect several marine species, from tiny fish and zooplankton to large turtles and whales.

Plastic pollution hazards to Australian species and ecological communities are therefore likely broader than those officially recognised.

Understanding the plastic pollution issue

Unfortunately, part of our plastic waste winds up in the oceans. Plastics can be transported from populated areas to the marine environment by rivers, wind, tides, rainwater, storm drains, sewage disposal, and flooding, or can directly reach the sea from boats and offshore installations.

Throughout their marine journey, plastics break down into increasingly smaller pieces mostly due to the effect of sunlight and heat.

These plastic fragments, commonly called microplastics when smaller than 5mm, represent the vast majority of human-made debris present at beaches, seafloor, and in the water column.

The effects of plastics on food webs and ecosystems have become focus of concern over the last decade. It is now known that over half of our plastic objects contain at least one ingredient classified as hazardous.

To make matters worse, plastics that enter the oceans become increasingly toxic by adsorbing oily pollutants on their surface. When plastic is ingested, these concentrated toxins can be delivered to animals and transferred up their food chains.

This biomagnification of toxins is more likely to occur when plastics are small enough to be ingested by low trophic fauna, such as small fish and zooplankton.

These tiny ocean plastics may affect the health of entire food webs, which include humans. For instance, little plastic pieces were found in the stomach of some Southern Bluefin tuna captured off Tasmania and destined for human consumption.

What kind of plastic and where does it come from?

Until now, plastic contamination in Australian waters was mostly inferred from beach clean-up reports. There was no at-sea survey focused on sampling plastic debris in waters around this country.

I wanted to fill this gap. During my PhD research, I went on seven transit voyages aboard three Australian vessels: RV Southern Surveyor, RV Solander, and Comac Enterprise.

During these trips, I used a net called Manta Net to catch floating plastics at the ocean surface.

Small fragments of hard plastic were the most common type, but soft plastics, such as fragments of wrappers, and strings (mostly fishing lines) were also common.

Harmful Plastics Graph

Size and types of marine plastics collected around Australia. Examples of each plastic type are shown in the photos. Image: PLOS ONE

These plastics were mostly made of polyolefins (polyethylene and polypropylene). These polymers account for 52% of our plastic production and are typically used to make throwaway packaging. They are also used for manufacturing fishing equipment such as crates, nets, ropes, and lines.

Our overall mean sea surface plastic concentration was 4,256.4 plastic pieces per km2. This mean value is higher than those reported for other regions, such as the Caribbean Sea (1,414 pieces per km2) and Gulf of Maine (1,534 pieces per km2).

However, in the subtropical gyres, plastics tend to accumulate due to converging ocean currents, and mean plastic concentrations are higher: from 20,328 pieces per km2 in the North Atlantic Gyre, to 334,271 pieces per km2 in the North Pacific Gyre. The Mediterranean Sea is also a global hotspot for plastics: it has around 116,000 plastics per km2.

We observed higher plastic concentrations close to major Australian cities (Sydney, Brisbane) and industrial centres (Karratha) as well as in remote areas where ocean currents converged (such as south-west Tasmania).

Harmful Plastics Concentrations

Marine plastic concentrations in waters around Australia. White crosses indicate location of major Australian cities. Image: PLOS ONE

These observations, along with our ocean current modelling results, indicate that marine plastics reach Australian waters from multiple sources: domestic and international populated areas, as well as maritime operations.

Solutions

Plastics, made mostly of oil and gas, are cheaper than the natural materials they replace for the manufacture of many objects, such as packaging and fishing gear.

As a result, incentives to re-use or recycle every-day items have decreased over the last few decades. Meanwhile plastic production has increased from 1,700,00 tonnes in 1950 to 280,000,000 tonnes in 2011.

In Australia, 1,476,690 tonnes of plastics were used in 2011-2012, of which just 20.5% was recycled. Most of these plastics (around 37%) were used for manufacturing single-use disposable packaging, including plastic bottles, cups, and bags.

Marine plastic pollution is a global issue caused by our massive production of plastic waste. The solution for this recent environmental problem is not simple.

We believe there are three important steps. First, decrease plastic waste: this could be achieved by reducing production of single-use plastic packaging. Second, improve our plastic disposal practices on land at an international level. And last, better enforce the laws prohibiting dumping of plastics at sea.

Disclosure Statement

Julia Reisser is a PhD candidate at the University of Western Australia, and receives funding and support from the University of Western Australia and CSIRO Wealth from Oceans Flagship.

Charitha Pattiaratchi does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article.

This article was originally published at The Conversation.
By Julia Reisser, University of Western Australia and Charitha Pattiaratchi, University of Western Australia
Read the original article.