Elizaveta Ivanova

The Attractive Odors of Marine Plastic

December 22, 2020

It has been long assumed marine animals eat plastic because they visually mistake it for prey. However, a recent study suggests this ingestion may actually be the result of the aromas that marine plastic debris emit. Lethal consequences were seen along Tel Aviv’s coastline.

September 30th began like any other day for me, a walk along the shoreline of Trumpeldor Beach. Except this time, I was witness to a tragic incident of a giant sea turtle that had washed ashore. As I walked closer to it, I can distinctly remember the exact moment where my feelings of excitement turned into sadness. I thought to myself, “Wow, this is the first wild sea turtle I have ever encountered in my life,” before thinking, “Oh, it’s dead.” A sharp wave of numbness and complete ignorance caught me off guard. I was naive thinking various maritime disasters only really occur in distant places like Australia and Oceania’s shores and that the Mediterranean Sea was unaffected by such tragedies.

As I and others examined the deceased sea turtle, we deduced the turtle’s death was the result of plastic materials blocking its digestive system. Plastic bags were sticking out of the turtle’s gut, and its legs were wrapped in a fishing net. After further investigation, it appeared as though the turtle’s death occurred at some point well before it washed ashore as the body had already begun to deteriorate. This also made identifying its species complicated. 

Naturally, this encounter left me feeling uneasy. In a way, I myself felt guilty because of my connection to a society that routinely litters plastic and commits similar acts of environmental injustice. Environmentally inconsiderate actions and behaviors such as this will most likely continue to degrade all existing ecosystems land and especially marine ones, unless we take active measures to stop it.

Smells like Food 

In recent years, many marine wildlife species populations have fallen victim to harsh decline—sea turtles especially. Many experts have drawn a link between higher mortality and the overwhelming presence of plastic waste and plastic debris reaching marine habitats. But the question scientists are seeking to answer is what exactly motivates animals like sea turtles to consume plastic material?

It has been generally understood that sea turtles are primarily visual predators and consume plastic as a result of a visual error, mistaking material like a floating plastic bag for prey such as jellyfish. However, industrial fishing debris such as ropes or nets, bear no clear resemblance to jellyfish, algae, or other soft-bodied invertebrates. Yet it is common for sea turtles to become entangled in it. This circumstance casts doubt on the “plastic-jellyfish” hypothesis, making an additional claim that visual cues might not be the answer.

However, a study published in Current Biology provides new evidence to explain what causes sea turtles to ingest plastic materials in the first place. This finding suggests that marine animals may be attracted to plastic debris not only by its appearance but more so by its smells. “The same airborne odorants used by marine predators to identify prey and locate areas of elevated ocean productivity also emanate from marine-conditioned or ‘biofouled’ plastic debris,” write a team of researchers from the Caretta Research Project in Savannah, Georgia.

Marine biofouling on surfaces is usually first comprised of organic substances, bacteria, and other microorganisms such as microalgae, and later also include small marine invertebrates. Such an assembly of organisms develop on surfaces that enter the marine environment including plastic waste and debris. This process provides a favorable environment for the growth of these organisms, which in turn produce a pleasing odor for animals in search of food.

To test whether aromas from biofouling plastic debris could lure unsuspecting turtles into swallowing indigestible plastic, the researchers experimented with 15 captive-reared loggerhead turtles (Caretta caretta). They were placed in tanks that allowed researchers to inject odors, and they videotaped their response to four different odors (food, clean plastic, biofouled plastic and distilled water). Ultimately, the researchers found that the aromas of food and biofouled plastic elicited nearly identical responses from the loggerhead turtles.

“These results indicate that sea turtles can detect airborne odorants emanating from biofouled plastic and respond to them in the same way that they respond to food odors,” the researchers write in the study. “Moreover, these findings are consistent with the hypothesis that odors emanating from biofouled plastic stimulate foraging behavior in sea turtles and contribute to turtles’ attraction to marine plastic debris.”

Even though many perished sea turtles are found with plastic inside their digestive tract, it is sometimes not the sole cause of death. Many turtles die from suffocation due to entanglement in fishing gear or due to severe injuries caused by marine vessels. Regardless, interaction with marine plastic presents significant threats to the wildlife and the ecosystem in which they are supposed to thrive. As this study has made clear, fully understanding the interactions between wildlife and plastic debris is critical for establishing effective mitigation efforts going forward. 

Extent of Israel’s Plastic Problem

According to the 2019 World Wildlife Fund Report, Tel Aviv ranks third among 21 Mediterranean cities in coastal plastic pollution, following the coastlines of southern Turkey and Barcelona. The IUCN’s Global Marine and Polar Program reports that an estimated 229,000 tons of plastic are leaking into the Mediterranean Sea annually—the equivalent to over 500 shipping containers each day. 

On average, every one kilometer of Tel Aviv coastline accumulates 21 kilograms (46 lbs) of plastic debris per day, 66% of which consists of plastic bags and packaging waste. Unless significant measures are taken to eliminate mismanaged waste products, this amount is projected to double by 2040.

Unfortunately, the COVID-19 pandemic has exacerbated marine pollution as face masks, gloves, and empty hand sanitizer bottles have been found in the Mediterranean alongside usual artificial litter. Other than acknowledging the extent of the problem, I wondered what I and others could do to assist marine protection.

What You Can Do

The status of the Mediterranean’s plastic pollution is definitely daunting and certainly highlights the extent of humanity’s impact onto the environment. However, we can begin to rectify the damage done by rethinking and changing our daily habits as a way to reduce the amount of waste reaching marine environments. In doing so, the mortality rate of marine dwellers like the sea turtles could be decreased. Here are a few easy steps:

Familiarizing yourself with the Israeli Sea Turtle Rescue Center is a good start. This organization works to provide safe environments for turtles in need of treatment. They also provide tours and lectures to the public that inform visitors of how best to handle a beached sea turtle entangled in netting, string, or plastic material. Alternatively, those who may come across a distressed sea turtle can call the rescue center’s hotline at *3639 and await assistance.

In terms of daily behavioral change, actively investing in reusable goods would be highly beneficial as 65% of plastic consumed in Mediterranean countries becomes waste within a year, with single-use packaging items being the biggest source of waste. Reusable coffee cups, water bottles, bags, and food containers can significantly reduce the overall human ecological footprint.

Lastly, perhaps the most feasible action one can take is merely picking up trash when it is seen. Grassroots movement, Plastic Free Israel, organizes numerous beach clean-ups where interested volunteers can lend their help in collecting mass amounts of various litter. By making personal changes or participating in organizational campaigns, effectively rehabilitating the Mediterranean can be within our grasp.

This article was also published in The Jerusalem Post on 12 Dec. 2020