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Plastic Litter on Beaches Makes them Hotter by Day, Colder by Night

Plastic litter
Plastic and other litter on a beach in Accra, Ghana. Plastics not only are unsightly and endanger wildlife, they also make beaches hotter in the daytime and colder at nights according to new research. Credit: Muntaka Chasant/Creative Commons Attribution-Share Alike 4.0 International

New research shows that not only does plastic litter desecrate the beauty of beaches around the world — it actually makes them hotter by day and colder at night, changing the environment that is home to beach-dwelling creatures such as birds and turtles.

The study, undertaken on islands that ring the notorious “Pacific garbage patch,” the floating miasma of discarded floating detritus that has formed in the middle of the world’s largest ocean, points to yet more issues caused by the prevalence of plastics in our waters.

Henderson Island, located in the Indian Ocean, is on the western edge of the infamous rotating mound of castaway plastics and abandoned nylon nets.

Several years ago the otherwise idyllic island, covered in palm trees and with white sand beaches, was in the news as researchers weighed all of the litter that had made its way onto Henderson. They came up with an appalling number — 18 million tons — despite the island being situated literally thousands of miles from any major land mass.

This same team of scientists have now made an even more surprising discovery, perhaps – that the presence of plastic litter on beaches alter the temperatures of the sand there, as well as on the Cocos Islands, further off in the Indian Ocean.

The Journal of Hazardous Materials published the team’s report on their findings, showing that such detritus poses yet another problem for animals such as crabs, mussels and snails– which are very sensitive to these temperatures as they spend their lives on the sand.

Shore birds, turtles greatly affected by beach temperatures

Other, more prominent animals, such as shore birds and sea turtles, which use beaches for vital nesting areas, are also affected.

As anyone who has paid attention to wildlife news knows by now, wild animals often fall prey to plastic pollution in our seas, ingesting both small and large pieces of it and finding themselves caught in abandoned nets.

More insidiously, the ingestion of plastics can even give animals a false sense of fullness, so they stop eating; then microplastics can leach their chemicals into the bodies of sea animals, prompting organ failure and possibly even reproductive failure.

The long-term effects of these harmful chemicals on the individual cells of living organisms are still being studied.

Jennifer Lavers, a marine toxicologist from the University of Tasmania in Australia, took yet another tack in her research, looking into how plastics also alter the temperature of the microenvironment in which many sea and littoral-dwelling creatures live.

“Up until this point, so much of the literature focused on charismatic species or the type or source of plastic,” Lavers writes in her study. “Year after year, I’d return to some of the most far-flung corners of our planet and the plastic I witnessed 12, 24 months ago would still be sitting there (except perhaps even more!). I knew it had to be having some kind of effect, but there was no data.”

In order to try to get a handle on how this litter impacted the lives of animals, Lavers and her team studied ten, three square-foot plots on both Henderson and the Cocos Islands.

After counting every piece of plastic litter they found in the plots, they installed thermometers at two depths, at both two and 12 inches deep in the sand, according to Smithsonian Magazine.

Researchers could not locate pristine area of sand for control in study

But one thing was lacking — a clear area of sand that had no such litter on it to act as a control mechanism.

Jack Auty, an interdisciplinary biologist at the University of Tasmania who headed up the data analysis for the experiment, lamented “They couldn’t find a blank space as a control site.”

According to the team, there was simply nowhere on these almost-deserted Indian Ocean islands that had been left pristine — so they had to use the area with the least garbage on it as the control site.

After measuring the sand temperatures for the duration of three months, Auty further analyzed it by hour and by day. “I could see the story coming out as I explored the data,” he explains, adding “I began to see how the (temperatures’) circadian rhythms were being massively impacted by the surface levels of plastic.”

In shallow sandy plots having what the team considered to be “moderate” levels of plastic, the highest daily temperatures were approximately 2.5 degrees Celsius warmer than other sites that they considered to be sites having little or a great deal of plastic litter.

Not only that but their daily minimum temperatures were approximately 1.5 degrees cooler as well, showing a large range of temperatures over the course of a day.

As soon as the layer of plastic detritus became too deep, the differences in temperatures waned, as it did when the temperature seniors were placed deeper in the sand.

Greenhouse effect with transparent plastics

“Interestingly, even the hot effect disappeared for the highest level of plastic, where you can’t even see the sand,” Auty explains, since “Light can’t penetrate there. At that point, the sand is buried so deep under plastic that it just can’t go through that extreme circadian cycle.”

The daytime warming of the sands, the researchers believe, may be due to the insulating effect from the plastic — as you can imagine, clear plastics form almost a greenhouse, trapping heat and moisture inside them as the sun beams down on them all day.

However, what happens at night, Auty says, is “perplexing” since one might imagine that there would be no difference on clean beaches vs. littered ones after the sun goes down.

Amazingly, plastic litter on sand might actually create a pathway for air and water to dissipate the collective heat of the sands after the sun ceases to beat down on it; the researchers say they must conduct further studies to pinpoint the exactly how this occurs.

However, just like in the atmosphere, the difference of a few degrees in temperature in the sand is noticeable and may make all the difference in the lives of animals that are completely dependent on the beach environment in order to live.

In addition, the problem as observed on the Indian Ocean islands may be even more noticeable in the higher latitudes, which have an even greater difference in their normal daily temperature ranges.

Animals living on equator not used to temperature changes

But in the equatorial zone, animals are acclimated to an environment which does not have much variation in temperature whatsoever — so leaving them to deal with surroundings which experience relatively large temperature swings due to litter may be a life or death issue.

Sea turtles, which are cold blooded and which are very dependent on beaches for their reproduction and survival, are seen at particular risk now that the temperature issue is known.

“Reptiles are ectotherms — they’re cold-blooded — and they’re intrinsically tied to the thermal characteristics of their environment,” explains Leo Clarke, a marine ecologist at Wales’ Bangor University and who was not a part of the study. “So temperature influences lots of parts of their life cycle, and reproduction in particular.”

Research has already shown that nest temperatures affect the sex ratios of baby turtles, whose mothers lay their eggs in beach sand. Warmer nests result in more young females, skewing the sex ratio in animals which already face many challenges to their survival.

High beach temperatures adversely affect baby turtles

Overly high temperatures have also been shown to decrease the fitness and the eventual survival rate of turtle hatchlings, with stronger, larger individuals originating from nests that enjoyed cooler temperatures.

Experts believe that other ectotherms, such as tropical iguanas, might be affected in a similar way.

One bright spot — at least for turtles — is that the researchers found there was little temperature variation at the depths at which loggerhead turtles make their nests.

But other beach dwellers who live right on the surface of the sand are sure to be impacted by such temperature swings, says Stephanie Borrelle, an environmental ecologist who was also not involved in the study.

“If there’s plastic at the nest sites and it’s incorporated into nesting materials or into the burrows, and that’s increasing the temperature, that could potentially have impacts on the development of an egg or a chick,” she explains, adding “That’s a big, important question for us to start looking at. We’re really at the beginning of trying to understand it.”

Of course, there is sure to be an effect on the microscopic level regarding these swings in temperature, with bacteria and small invertebrates such as barnacles highly sensitive to temperature.

This means more extreme high and low temperatures could allow some organisms to thrive while others die. “We talk about sea turtles because they’re charismatic, but temperature changes would also affect invertebrates and microorganisms and soils,” Auty states.

“They’re really the foundation for coastal, intertidal ecosystems, and they could be incredibly vulnerable to these temperature changes.”

Problems at bottom of the food chain mirrored everywhere else

And obviously, these much smaller creatures form the bottom of the food chain in the littoral world. “If plastics in burrows affect the soil biota, that could impact mites or other disease-carrying microorganisms,” says BirdLife International’s Borrelle.

“With climate change, that’s already an issue for seabirds,” she adds.

The kind of temperature swings caused by plastic litter on beaches could even worsen the spread of diseases such as avian malaria. A ripple effect, as is seen in all other types of human and animal environments, leads to a range of ramifications down the line with other species.

Borrelle is not especially sanguine regarding the worldwide elimination of plastic litter, telling reporters she even came across plastic bottle rings while she was doing research on the continent of Antarctica.

If it is indeed too late to clean up all the plastic litter on beaches, scientists need to find a way to support the species that are being impacted by this and other environmental threats now.

Animals must adapt to human-caused dangers

“Unfortunately, it’s like climate change. We’ve already done a lot of damage to the environment with plastics,” she explains, adding “So at this point, I think it’s more about finding ways to mitigate other threats and buffer those populations to try and avoid further declines, or the cumulative impact of multiple threats.”

An ability to adapt to this ugly reality is important if these beach-dependent animals are to overcome these stresses, agrees Bangor University’s Clarke.

“The populations with the most potential to adapt and to be resilient to environmental change are healthy ones, so conservation efforts need to focus on not just temperature and climate change, but all threats turtles face, from pollution, to overfishing, to exploitation,” he says.

Still, mankind must address the underlying issue to begin with, according to Auty, who says  “We have filled the atmosphere, the oceans, the world with plastics, and there’s no way to reverse it, which is terrifying.

“There really is only one solution, and that is to stop buying and producing plastic. And then hopefully things will recover.”

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