Biodegradable plastic signifies false hope for threatened Mediterranean seagrass community

A blog post on seagrass by our IYOR intern, Talia Wong. Enjoy!:

4_Seagrass_taken from Time Magazine

At a 100,000 year old, Posidonia oceania meadow is one of the oldest things on Earth and it has been reported that they are also one of the most important carbon sinks in the area. Unfortunately, like Cymodocea nodosa, this species is also highly threatened. (Photo: Time Magazine)

Not a solution but creation of biodegradable plastic is an inventive step in trying to “reduce” our plastic footprint.

Plastic pollution, the bane of the 21st century. Today, an unprecedented amount of plastics accumulates and drifts in the world’s oceans. With countless disturbing images of turtles, seals and other marine creatures photographed caught in plastic trash and beaches filled with plastic bottles now etched into our minds, some countries are scrambling to be rid of this marine hazard by banning and replacing it with biodegradable plastic. So far, Vanuatu, is the only South Pacific nation in the world that officially bans the consumption of plastics.

While marine creatures are receiving much media attention due to their charismatic public appeal, little is known about the effects of plastics on the seagrass community.

Not the most exciting, cute or annoying species on the planet, majority of the world’s population have hardly heard of seagrass. Sometimes even classifying them as the marine macroalgae, “seaweed”.

Seagrass has been understudied and undervalued. It turns out that they exist in many parts of the world! Seagrasses are found in shallow coastal waters and estuaries across the world’s ocean floor (except Antarctica). These communities live either as a single specie community or coexist with other species of seagrass communities.

It is easy to dismiss a flourishing seagrass meadow as a useless and unimportant patch of grass. Sadly, this is the unavoidable and tragic reality of life when there is limited knowledge and exposure about the topic.

A vibrant and lush seagrass meadow not only maintains marine biodiversity by serving as a nursery for most juvenile reef fishes, it regulates coastal water quality, serves as coastal defence and storm buffers and plays a fundamental role in structuring communities – just to name a few.

Unfortunately, many species today face an uncertain future.

With the trickle-down effect of climate change such as ocean acidification, warmer waters, sea level rise (which will affect the amount of light reaching the seabed) and local stressors such as point source pollution, eutrophication and trawling activities to deal with, these clonal marine flowering plants are helpless against these pressures.

And, to make matters worse, plastic trash comprise a major component of marine litter. It has been reported that for every hectare along the Italian coat, 14 conventional bag fragments can be found lying near seagrass meadows.

Thankfully, our ability to create and innovate has not failed us. We can proudly proclaim that biodegradable plastic now exists although its use is not as ubiquitous (yet).

These bags are made from renewable raw materials like corn starch, cellulose or biosynthesized materials. Being denser, these bags will only remain at the sea surface for 10 to 25 minutes before sinking to the bottom of the ocean unlike conventional plastics which remain suspended near the surface for a longer time.  

Whilst on the ocean floor, these new bags supposedly degrade into water, carbon dioxide, methane and biomass when it interacts with microbial organisms. Such a scenario paints a rosy picture for humanity. It would mean one less anthropogenic hassle to deal with from the list of urgent issues to tackle. It would allow us to focus our attention on other pressing matters like limiting global warming under 2 degrees Celsius.  

However, a new study published in the journal of Science and Total Environment in July 2017 by biologists from the University of Pisa noted that these new generation bags are not as degradable as they were made out to be. While these bags have been validated and certified as compostable and biodegradable, they were tested in non-marine environment settings and are so not telling of their actual ability to disintegrate in the ocean.  

What made this outdoor study different was its use of natural marine sediment (silica sand) and constant flowing seawater to recreate the marine environment. The study examined the bag’s degradation rate under those conditions and brought in common Mediterranean seagrass species, Cymodocea nodosa and Zostera noltei to understand the bag-seagrass interaction.

Biodegradable bags (made of vegetable oil and corn starch) and cellulose filter paper (control) were cut up in small, standard sized pieces and buried in silica sand to mimic the seabed for the first experiment. And for the second experiment, standard sized biodegradable bags are placed in 3 types of setups consisting of 1 specie, 2 same species and 2 different species respectively.

After 6 months of sediment exposure, the bag pieces recorded negligible degradation while the control cellulose filter paper underwent substantial degradation. The bag showed initial signs of surface disintegration (cracks and holes) when studied under a microscope and displayed notable discolouration from white to pink and yellow. Nonetheless, the bag retained 85% of its initial weight whereas the filter paper lost 60% of its initial weight.

It was noted that the presence of the bags altered the seabed geochemistry. Temperature and oxygen concentration of the sediment were lower than before as the bags acted as a barrier against gas and heat exchange between the seawater and the sediment.

Consequently, the seabed acts as a sink for bioplastics. It becomes more apparent in temperate waters where water temperature is lower and less conducive for decomposition.

And, of course, we have forgotten about the seagrass community (yet again).

The presence of seagrass counteracts these changes.

The Mediterranean seagrass species reverse the geochemistry changes of the sediment. Its natural metabolic activities raise sediment temperature. And for species like Z. noltei, it releases oxygen into the ground to establish more favourable seabed conditions for root growth and to protect itself against any nearby reduced phytotoxic compounds.

In relation to plant growth and plant-plant interaction, the results of the study conclude that the bag increases competition for space and resources between specie(s), both in monospecific and mixed meadows. So, the presence of the biodegradable bag introduces yet another local stressor to the seagrass.

Consequently, the presence of these bags on the seabed acts just like highways cutting through terrestrial forests causing spatial fragmentation within the seagrass community. Like the terrestrial setting, fragmenting the seagrass ecosystem leads to habitat destruction and isolation leading to the formation of discontinuities within the original seagrass area. These discontinuities hinder genetic flow and reduce diversity and thus, weaken the resilience of the seagrass community to future disturbances.

Even as these biodegradable bags become the plastics of the near future, to end off on a positive note, they hold potential for future success.

In these outdoor stimulations, the controlled natural environment was sufficiently microbial active to degrade the cellulose and starch materials. This potentially suggests that marine environment itself already holds an important key to success. Furthermore, given the differential degradation rates of the filter paper and the bag pieces, the actual rate of bio-plastic deterioration really depends on the composition of the bag and its local context. Granted that the experiments conducted tried to emulate the real marine environment, the lack of wave abrasion and amount of ultraviolet radiation cannot be replicated.

For now, biodegradable plastics offers us a dim light amidst despair as it paves the way for better innovations. And as this new study shines more light onto the interface between bioplastics, sea grass and sediment bed, it creates more opportunities for further research into the long-term impacts of biodegradable plastics and the deterioration success of different types of bag compositions.

Regardless of this technological breakthrough, our plastic problem cannot be swept under the rug and forgotten.

Let us all keep in mind that plastics – biodegradable or not – are not natural entities that belong to the marine world and we should do our best to keep them out of it.


Balestri, Elena et al. “Biodegradable Plastic Bags On The Seafloor: A Future Threat For Seagrass Meadows?.” Science of The Total Environment 605-606 (2017): 755-763.


Next blog post by our IYOR intern, Talia Wong, on marine trash:

4_Blogpost1_Cover photo

In the summer of 2017, I was fortunate enough to intern at Marine Conservation Cambodia where I learnt more about the marine life surrounding near the island of Koh Seh, specifically on seahorses. Concurrently, we were doing beach clean-ups every few days. In our bags were the usual culprits like wood planks, toys, lighters, rubber bands and slippers, glass bottles, plastic containers, caps and cutlery … But as Southeast Asia boasts one of the strongest fishing industries in the world, it came as no surprise when we found loads of fishing float hooks, fish and crab cages (big ones that weigh at least 7kg!), nets all which broke away from their fishers. What stunned (and honestly, scared) me the most was the medical trash we found such as syringes – some with needles still attached – forgive my ignorance, it was my first time picking them up during a beach clean-up.

Most of the rubbish picked up had Vietnamese wordings on them. And this magnifies the scale of trash further. The reason why I brought this up wasn’t to finger point someone but to show how trash is borderless and it is more imperative for administrations to work together.

Simply conducting beach clean ups daily or every week is not enough and in the long run, ineffective. And, utilising debris skimmer boats is costly with engines that require constant maintenance and skills to power. These boats do not tackle the root of the problem as well.


Marine trash is anything that is man-made and doesn’t belong to the ocean. It can be intentionally dumped or unintentionally leaked into water bodies which then flows into our oceans. Catastrophic events i.e. tsunami, hurricanes or floods can carry out large amounts of it into the ocean. This waste includes glass, metals, paper, textiles, wood (although there is natural debris), rubber and plastics and it ranges from micrometres to metres in size.

Marine trash ends up either along coastlines or accumulates and circulates in the centre of gyres due to current patterns. Currently, there are 5 known gyres where debris accumulates with the North Pacific Ocean gyre, also known as the ‘Great Pacific Garbage Patch’ being the most well-known due to its size.

This floating dock carried an ecosystem of non-native, invasive species from the Western to the Eastern Pacific coast. (Photo: NY Times)
This floating dock carried an ecosystem of non-native, invasive species from the Western
to the Eastern Pacific coast. (Photo: NY Times)



Since its introduction in the late 1800s, plastic has become so intimately interwoven into our everyday lives and has led to the flourishing of economies and societies. Yet, as much as we depend on them, we toss them out more easily. In doing so, we upset the balance of the marine ecosystem.

A shocking amount of plastics completely covering parts of the Caribbean Sea. (Photo: Caroline Power Photography)
A shocking amount of plastics completely covering parts of the Caribbean Sea.
(Photo: Caroline Power Photography)

Plastic accounts for the most abundant material collected as marine trash and this poses severe consequences for marine life. At the end of 2017, a viral photo of a lone seahorse holding onto a discarded cotton swab for dear life depicted the grim reality of our plastic pollution.

Photo: Justin Hofman, National Geographic Wildlife Photographer of 2017
Photo: Justin Hofman, National Geographic Wildlife Photographer of 2017

Common interactions between marine life and trash consist of entanglement and ingestion which often lead to external or internal injury and ultimately, death. Floating debris could bring invasive species into the new site and potentially upset the existing ecosystem balance. Debris found on the seafloor have also been proven to interfere with light penetration and the exchange of oxygen.

Last but not the least, it gets personal. Through bioaccumulation and biomagnification of toxic additives found in plastic, marine life who have successfully consumed the plastic and are caught by fishermen could mean that the toxins end up on our plates and basically into our bodies. And for all the fishers and sailors out there, marine trash are navigational hazards and can possibly sink their boats.

At the start, I mentioned about all the medical trash that comes in waves and it’s true not just at Cambodia. During the late 80s, there was an environmental disaster known as “The Great Syringe Tide” over in the United States. Fearing injury, beaches along the Atlantic coast were closed and tourism took a dip.


Well, we all know what I’m going to say next. And instead of sounding like a broken record – which I hope that hasn’t been the case so far – why not start by ditching those single-use items and invest in something durable. For example, rather than using disposable straws, purchase bamboo or metal straw or better yet, go without a straw and drink right out of the cup/glass!

On a larger scale, coastal cities play a vital role in developing proper waste management systems as their growing numbers already places high pressure on the environment. Improper and irresponsible waste disposal is a stressor which we can minimize. It also reduces the possibilities of them getting swept out by retreating tsunami or storm surges into the ocean.

Today, innovative solutions that deals with our ever-increasing plastic waste are popping up. One of them involves the construction of roads using waste plastic. Since plastic is very durable, it fits seamlessly into the idea of constructing roads that will last and are not as vulnerable to cracks and potholes.

With our oceans slowly suffocating and dying, the increasing awareness and knowledge on marine trash has created and sustained a greater movement towards minimizing our plastic consumption. Be it by national governments or in schools, we deserve a pat on our back. And unless we want plastic on our plates, as individuals, we should work towards reducing our plastic footprint.

You can check out this awesome documentary: A Plastic Ocean

And here’s the extent of the plastic pollution in the Caribbean Sea.

Till next time!

References journal articles

Axelsson, Charles, and Erik van Sebille. “Prevention Through Policy: Urban Macroplastic Leakages To The Marine Environment During Extreme Rainfall Events.” Marine Pollution Bulletin, vol 124, no. 1, 2017, pp. 211-227. Elsevier BV, doi:10.1016/j.marpolbul.2017.07.024.

Cozar, A. et al. “Plastic Debris In The Open Ocean.” Proceedings Of The National Academy Of Sciences, vol 111, no. 28, 2014, pp. 10239-10244. Proceedings Of The National Academy Of Sciences, doi:10.1073/pnas.1314705111.

Green, Dannielle Senga et al. “Impacts Of Discarded Plastic Bags On Marine Assemblages And Ecosystem Functioning.” Environmental Science & Technology, vol 49, no. 9, 2015, pp. 5380-5389. American Chemical Society (ACS), doi:10.1021/acs.est.5b00277.

Law, Kara Lavender. “Plastics In The Marine Environment.” Annual Review Of Marine Science, vol 9, no. 1, 2017, pp. 205-229. Annual Reviews, doi:10.1146/annurev-marine-010816-060409.

Löhr, Ansje et al. “Solutions For Global Marine Litter Pollution.” Current Opinion In Environmental Sustainability, vol 28, 2017, pp. 90-99. Elsevier BV, doi:10.1016/j.cosust.2017.08.009.

Rahul Prakash, K. V. et al. “Automatic Trash Removal System In Water Bodies.” International Journal Of Engineering Science And Computing (IJESC), vol 7, no. 4, 2017, pp. 6674-6678. International Journal Of Engineering Science And Computing (IJESC),

Rochman, Chelsea M. et al. “The Ecological Impacts Of Marine Debris: Unraveling The Demonstrated Evidence From What Is Perceived.” Ecology, vol 97, no. 2, 2016, pp. 302-312. Wiley-Blackwell, doi:10.1890/14-2070.1.

Uneputty, Prulley, and S.M. Evans. “The Impact Of Plastic Debris On The Biota Of Tidal Flats In Ambon Bay (Eastern Indonesia).” Marine Environmental Research, vol 44, no. 3, 1997, pp. 233-242. Elsevier BV, doi:10.1016/s0141-1136(97)00002-0.

Williams, Shawn. “Trophic Transfer Of Microplastics In The Marine Food Web.” 2017, pp. 1-28. Researchgate, doi:10.13140/RG.2.2.30917.96489.

Xanthos, Dirk, and Tony R. Walker. “International Policies To Reduce Plastic Marine Pollution From Single-Use Plastics (Plastic Bags And Microbeads): A Review.” Marine Pollution Bulletin, vol 118, no. 1-2, 2017, pp. 17-26. Elsevier BV, doi:10.1016/j.marpolbul.2017.02.048.