Microplastics and Manta Rays in Indonesia with Dr. Elitza Germanov and Janis Argeswara.

Dr. Elitza (Ellie) Germanov, a Senior Scientist at MMF, is a world expert on manta rays and ocean pollution. She started the Microplastics and Megafauna project in Indonesia as part of her PhD work, which studied the impact of the smallest plastics on the largest marine animals. Janis Argeswara joined the project as a Research Assistant in 2018 and is now leading a project on the reproductive ecology of manta rays. I talked to them from their research base on Nusa Lembongan, off Bali’s southeast coast. SJP

How did the Indonesian microplastics project begin?

EG: Manta research was developed here by our colleagues, Peter Bassett and Helen Mitchell, who had trained with MMF over in Mozambique. They moved to Lembongan in 2012 and started a great citizen science program focused on the mantas seen at the dive and snorkel sites over at Nusa Penida, a larger nearby island. I was working over in Komodo National Park, and we found that some manta rays were swimming the ~450 km between these two Marine Protected Areas. When I started my PhD on plastic pollution, Helen and Peter suggested that I should come over to Lembongan to work with them. They sent me a couple of horrific photos of mantas feeding amidst plastic off Nusa Penida during the rainy season. I was seeing plastics in Komodo too, but nothing I’d seen was as bad as that.

Why is ocean plastic pollution so bad around Bali?

EG: Nusa Penida is located in the Lombok Strait, where the Indonesian Throughflow current moves water from the Pacific Ocean to the Indian Ocean. There’s a lot of water moving past Nusa Penida, and it brings plastic and other trash right down from China and the Philippines. Manta rays like to feed around Nusa Penida because the island's points create eddies in the flow, which concentrate the zooplankton the mantas feed on into the bays. With so much plastic now being transported, this is being concentrated around the island too, which makes it unavoidable for the mantas.

That said, we do see a lot of local plastic as well. Bali has a dense population, and during the Indonesian rainy season we see over 20x more plastic at Nusa Penida than during the mid-year dry season. It's common for villages to just bring their waste close to the riverbank and burn it but, if the river overflows during heavy rain, that flushes the waste right down to the mantas at Nusa Penida.

What sort of plastic pollution are you seeing?

EG: Most of the identifiable trash, where we can see and read the labels, is Indonesian. We see a mix of consumer products, like plastic packaging for soaps, shampoos, and fast food, along with clear plastic bags that are commonly used in fisheries. Small-scale fishers will take these plastic tubes, fill them with ice, and bring them onboard the boats to keep their fish cold. Those tubes are very recognizable due to their shape. They're widely used in Indonesia, and likely in other countries to the north of us as well, so they could be coming from anywhere.

JA: Some of the recognizable waste is very old too – perhaps from the late 1990s – which illustrates the fundamental problem: plastics last in the environment for a really long time. 

EG: Each year's input compounds the issue. The plastic does disappear, eventually, but we're not sure where. Whether it's piling up at the bottom of the ocean or being ingested by marine life, we lose track of it. Hypothetically, it should be breaking down very gradually to its chemical and mineral elements, but that takes a very long time. It can do a lot of damage as it degrades.

What makes manta rays particularly vulnerable to ocean plastic?

JA: Manta rays are filter-feeders so, if there's a lot of small plastics in the water among the plankton they're targeting, it's difficult for them to avoid ingesting some of it. Mantas can vomit up plastic, but these small bits can add up and cause damage. Even small plastic pieces can add up to block or inhibit intestine function. 

EG: We've estimated how many microplastics the manta rays are ingesting while feeding here at Nusa Penida in the rainy season: about 63 pieces an hour.

How is pollution affecting manta rays?

JA: Even if the microplastics don't completely block the intestinal tract, like larger plastics can, the chemicals in the plastic can transfer over to the manta rays. Chemicals in the environment will bond to plastic, so if the plastic came from a river to the ocean, and that river was polluted, the plastics will have absorbed those pollutants. Once the plastic is out in the ocean, if it's ingested by marine wildlife, the pollutants in the plastic can leach out into the animal.

EG: We're still in the process of working out whether that's happening to mantas or not. But even if the plastics aren't acting as vectors for environmental pollution, the plastics can be toxic themselves. A lot of them are manufactured with additives, such as flame retardants, that aren't supposed to go into your body. We're hoping to be able to use small skin samples from wild mantas to detect the accumulation of industrial chemicals in their body. 

Reef manta rays, the species we're primarily working with here, are already threatened due to human pressures. Plastic ingestion could cause direct mortalities, but the accumulation of toxic chemicals in their bodies could also have chronic impacts on their reproduction, growth, and maturity. That's part of what Janis' project is looking at.

JA: We're monitoring individual growth rates, how many mantas are pregnant each year, and whether that’s changing over time. It's complicated, as there are also broader environmental changes that affect things like food availability, but we can start getting insight into how pollution is affecting manta populations. 

Manta rays are likely to be bioaccumulating higher and higher levels of pollutants like PCBs and pesticides that leach out from plastics. We know from other animals, including other sharks and rays, that a process called maternal offloading can be used to move pollutants from the mother to the baby during gestation, potentially as an evolutionary strategy to reduce the burden on the mother. With mantas potentially only giving birth to a couple of pups over their life, it doesn't bode well for this population if that's happening.

The problem of cumulative threats

EG: Plastic ingestion is just one of the stressors on the mantas. Over 10% of the mantas at Nusa Penida have permanent injuries from entanglement in fishing gear. The problem for mantas is that they can't swim backward, so they can end up with lines wrapped around them, which can cut their fins off or cause severe injuries that affect their ability to swim and feed. We always carry shears with us while we're diving in case we see an entangled manta we can help.

Fishing is an obvious threat, but we're also seeing climate change and the changes in larger-scale oceanographic processes that come with it, and other activities like tourism can be a problem if it disrupts their feeding or cleaning. That's where these additive problems like plastic are nasty – if it's slowly reducing the number of baby mantas being born, and then the survival of those babies, all these things will combine to cause population decline. We don't know where the breaking point will be.

What are the solutions to ocean plastics?

EG: This is the problem with studying plastics: it's depressing. One thing that I grab on to is the huge increase in awareness over the past few years. I'm seeing more people here be considerate and bring their own bags, more restaurants not using plastic straws, and the government has banned the use of plastic shopping bags. All the takeaway containers here now are made from cardboard. That's all happened in the last five years. Waste management is still a struggle, but at least there's less new plastic going into the system. 

Corporates have been trying hard to shift the responsibility for pollution onto consumers, but we need them to clean up the mess they've created. There are some encouraging signs. Aqua, a company that makes water bottles here, now sells a bottle that's completely recycled. The next step would be to have water refill stations everywhere, as they have in the Philippines, since the water from the tap isn't potable. 

When we find waste from specific companies we're always tagging them in our photos; it's like, hey, here's your Kinder Surprise out in the ocean choking manta rays. There are various projects focusing on cleaning up the environment, which is excellent, but we need to focus on not creating this waste in the first place.