Floating Plastic and Filter-Feeders: A Recipe for Disaster?
The topic of plastic pollution has recently taken the world by storm. Compelling photographs of marine animals trapped in nets and plastic bags have flooded social media, becoming hard to ignore. However, what may not be obvious from these viral images are the true effects of plastic on marine species. Today we’re exploring some of the major impacts of plastic pollution on marine life, and talk to one organisation that’s fighting back.
The Problem with Plastic
While there are many issues with our oceans being littered with garbage, today we’re focusing on three major threats that plastics pose to marine life:
1. Ingestion: When you hear of animals ingesting plastic, what are the first thoughts that come to mind? Sea turtles mistaking plastic bags for jellyfish? Seabirds regurgitating plastic into their chicks’ mouths (thanks Chris Jordan)? While these thoughts are graphic, they unfortunately only scratch the surface of plastic ingestion. Recent reports of whales washing up dead, with stomachs full of plastics are shedding light on the scale of the issue. Plastic is hardly nutrient rich, and by taking the place of digestible food they block digestion and cause false satiation, and animals starve. It is now clear that plastic pollution is a direct cause of death in marine animals, with a new study showing that a sea turtle that has ingested just one piece of plastic has more than a one in five chance of dying
2. Entanglement: This threat is as literal as it sounds. Marine animals can become trapped in many forms of plastic debris, such as lost fishing gear like lines and nets (ghost fishing), ropes, and even plastic bags. If the animal does not immediately die from drowning, it can be physically restricted enough to cause starvation, physical trauma, infections, and even boat strikes due to their inability to flee oncoming vessels. Combine threats one and two, and it is estimated that 1-2 million seabirds and over 100,000 marine mammals are killed per year by eating or become entangled in plastic.
A sandbar shark with a plastic chord wrapped around the head, causing damage to the gills. Photos: Kaitlyn McQueeney @sharkdiver_kaitlyn
3. Toxicity: While plastics are slowly breaking down (fragmenting) in the ocean, what is unfortunately happening at a much faster rate is the leaching of toxic chemicals into the water (and into the tissues of the animals that have sadly eaten them). Some of these chemicals can interfere with an animal’s reproductive system (endocrine disruptors), while others are suspected to cause cancer (carcinogens). This is a major problem because of two big ‘B’ words:
Bioaccumulation: The chemicals build up in the tissues of the individual animal, reaching fatal levels
Biomagnification: The concentration of chemicals in animals higher up the food chain is greater than those lower down, because each predator consumes animals that have already bioaccumulated the toxins in their tissues, and animals higher up the food chain tend to consume larger numbers of their prey
But Not All Hope is Lost, Meet: The Manta Trust
As overwhelming as this can all sound, the fight is not over. There are many organizations combating plastic pollution. The Manta Trust is a UK based charity at the forefront of global mobulid (manta and devil ray) conservation and research. Formed in 2011, the Manta Trust now works with over 25 Affiliate Projects around the world in order to turn the tide for these enigmatic rays. Their goal is a sustainable future for the oceans, where manta rays and their relatives thrive in healthy, diverse marine ecosystems. Mobulids are most at risk from Point 2, entanglement, and can be caught in items such as discarded fishing nets. The Marine Diaries interviewed Eleanor Gloster of Manta Trust to learn more on why plastic is not so fantastic, and find out what the Manta Trust is doing to combat this issue.
Eleanor, thank you so much for taking the time to discuss this topic with us. Please tell me a little bit about your yourself and your role at the Manta Trust.
I work with the core Manta Trust team doing a wide range of tasks including:
Each week is different and I’m constantly learning what incredible animals manta and devil rays are.
What would you say are the top issues with plastic pollution for rays?
The main plastic threat for manta and devil rays is entanglement in plastic fishing lines and marker buoys lines, as well as ghost nets - fishing gear that is lost and abandoned in the ocean (abandoned fishing gear is thought to make up 10% of all marine litter.) Mobulid rays need to keep constantly moving forward to push oxygenated water over their gills, and can quickly asphyxiate and die if entangled in fishing nets and lines. However, there are some amazing organisations (like this one), working globally to remove ghost nets and you can even buy products made from recycled fishing gear to support their work.
As Manta Rays are filter feeders, are they threatened by microplastics?
There have been lots of reports about the threats of microplastics to marine life in the media. However, there is currently no scientific evidence that manta or devil rays are threatened by microplastics. At the macro-level, ingestion of plastics by manta and devil rays poses a limited risk, when compared with other threats they are facing (such as the gill plate trade). Mobulids are intelligent animals; they make constant adjustments to avoid debris and are able to spit out unwanted items. However, further research is needed to investigate this area more thoroughly, and the Manta Trust is 100% behind moving towards eliminating single-use plastics.
Have you experienced an unforgettable moment in which you truly felt the gravity of plastic pollution on marine life?
I remember clearly when I was nine years old, seeing a dead seagull washed up on the beach with plastic fishing line wrapped around its neck. I was so angry that careless human actions had caused its death that I started all sorts of recycling campaigns at my school! That was over 30 years ago and it feels like the world is only just waking up to the tsunami of plastic that is churning in our oceans every day – I’d like to hope that in another 30 years we’ll see some real change.
Can you leave us with one last piece of advice for anyone struggling with the concept of how their personal actions can make a difference?
If everyone reading this cut their ‘single-use’ plastic in half this year – and then got five friends to do the same – the impact would be tremendous! Don’t be daunted – it’s a very achievable goal. We should not be buying materials that were envisaged to last a lifetime, only to use them once and then throw them away. There are many creative alternatives that you can come up with to replace single-use items too. For example, one of our supporters recently Adopted-A-Manta for her daughter’s class, rather than give out sweets in plastic bags for her birthday. Lots of small changes like this add up.