The ocean has long been the end of the pipe for plastic pollution, with ocean wildlife bearing the brunt of the overproduction and overconsumption of single-use plastics. The world now produces more plastics than at any point in history—hundreds of millions of tons each year—and more than 11 million metric tons are flowing into the ocean annually. That is equivalent to more than a garbage truck’s worth of plastics entering our ocean every minute.
How does plastic kill ocean animals?
When swallowed, these plastics can be deadly—causing blockages, twisting organs or even puncturing organ walls. Ingested plastics have been found in nearly 1,300 ocean animal species, including every family of mammals and seabirds, and all seven species of sea turtles. Concern about the ecological implications of plastic-induced death rates has fueled calls for policy solutions at every level of government, from the local to the international. However, it is hard to set policy goals without understanding the measurable risk plastic ingestion poses to these species.
Ocean Conservancy scientists, along with top researchers at the University of Toronto, Federal University of Alagoas in Brazil and the University of Tazmania, worked together to answer the question: how much plastic is too much? They sought to determine how much ingested plastic is likely to cause death in seabirds, sea turtles and marine mammals. In other words, we sought to figure out the actual number of pieces and volume of macroplastics (plastics greater than 5 milimeters) that those animals must have in their gut to cause death 90% of the time.
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How much ingested plastic does it take to kill an ocean animal?
We compiled data from more than 10,000 necropsies—animal autopsies—of seabirds, sea turtles and marine mammals collected between the years 1900 and 2023 where we knew both the cause of death and whether and how much plastic the animal had eaten.
The results were alarming. We were surprised by the very small amount of plastic it takes to kill a seabird. We found that rubber (the kind balloons are made from) is the deadliest form of plastic to seabirds when ingested. It only takes six small pieces of rubber—each, on average, smaller than a pea in size—to kill a seabird.
Sea turtles are also surprisingly vulnerable, given their massive size: Less than half a baseball’s worth of plastics is likely to kill one in two Loggerhead turtles. Shockingly, nearly half of all sea turtles in our database had plastics in their guts at their time of death, which is especially troubling when you consider that five of the world’s seven sea turtle species are International Union for the Conservation of Nature (IUCN) red-listed as threatened.
Our models found that marine mammals are especially vulnerable to the impacts of lost fishing debris, also known as ghost gear; when swallowed, with just 28 pieces—each smaller than a tennis ball—enough to kill a sperm whale. Additional key findings from our research for each of the animal groups we studied include:
- Seabirds
- About 35% of seabirds in our dataset had plastic in their digestive tracts.
- Roughly 5% of seabirds who had plastics in them died specifically from plastic ingestion.
- Hard plastics were consumed more frequently than all other material types, followed by soft plastics, fishing debris, rubber and foams.
- When a seabird consumes only three pieces of rubber, like balloon shreds, our models predict there is a 50% chance this consumption will lead to the animal’s death.
- Marine Mammals
- In marine mammals, fishing debris was the most frequently ingested plastic material, followed by soft plastics, rubber, hard plastics, foam and cloth.
- Roughly 12% of marine mammals in our dataset had plastic in their digestive tracts.
- Nearly 6% of marine mammals from our dataset with plastics inside died as a result of eating those plastics.
- When a marine mammal consumes just 12 pieces of soft plastic—like grocery bags—our models predict a 50% chance this action will lead to the animal’s death.
- Half a soccerball’s worth of soft plastic (by volume) is enough to kill 90% of individuals in most seal, sea lion, dolphin and porpoise species.
- Sea Turtles
- In sea turtles, soft plastics like grocery bags were found to be the most frequently ingested plastic material, followed by fishing debris, hard plastics, foams, rubber and cloth.
- Nearly 50% of individual sea turtles in our dataset had plastic in their digestive tracts
- About 9% of turtles that ingested plastic in our dataset died as a result of eating it.
- Over 4% of all turtles in our dataset died directly from plastic ingestion.
- Just 1.5 golf ball’s worth of plastic (by volume) is enough to kill 50% of adult loggerhead sea turtles.
What can this research do?
This research emphasizes the risks macroplastic pollution poses to the life of marine animals, and the risk varies by species and plastic type. Our findings provide key insights to inform future research and policy actions aimed at reducing plastic pollution and the harm it causes to ocean wildlife and ecosystems. These results also underscore that important interventions like beach cleanups and better management of plastic waste are critical for protecting marine species. Because some types of plastics are deadlier than others when swallowed by marine life, policies targeting those specific items (e.g., plastic bags and balloons) can play an important role in protecting vulnerable species from the harms of plastic pollution in the future.
It is imperative to tackle the global plastics crisis by taking actions at all levels, from local to federal to international. In the U.S., bills like the REUSE Act—bipartisan legislation that would require examination and enhancement of existing reuse and refill systems—is just one way to make a difference. Add your name now and call on lawmakers to support and pass the REUSE Act.
The post Does Eating Plastics Really Kill Ocean Animals? appeared first on Ocean Conservancy.
Welcome to Cádiz
When we arrived in Cádiz in April, we knew that we would be spending the next months working on an experiment about underwater soundscapes. What we did not yet know was how much of our time would be spent carrying equipment through the city, rebuilding experimental frames, solving technical problems and trying to convince various pieces of equipment not to end up at the bottom of the Atlantic.
Cádiz itself was a pretty good and beautiful place to start.
The city is located at the very tip of a narrow peninsula and is surrounded by the Atlantic on almost all sides. There are beaches almost everywhere, small streets leading through the old town, the harbour with its many boats and plenty of places where you can simply sit down and watch the sea. It did not take us long to understand why Cádiz is sometimes called La Tacita de Plata, the Silver Cup.
Our first evening was still fairly relaxed. After arriving and settling in, we went out together for a drink and explored a little bit of the city. It was a good introduction to our new home. The next morning, however, the relaxed part was over and GAME 2026 officially began for us.
Our project focuses on how underwater soundscapes may influence the colonization of hard surfaces by marine sessile organisms. To investigate this, we used standardized PVC settlement panels mounted on experimental frames and exposed them to different underwater soundscapes.
Over the course of the experiment, we monitored which organisms settle on the panels and checked whether the developing communities differ between the different acoustic conditions. The panels themselves were only 15 x 15 cm in size, but the frames, which were holding them while they were underwater, were much larger and required quite a bit of construction and preparation.
So, before we could investigate anything, however, we had to build everything.
Building the experiment
The first weeks in Cádiz were all about getting the experiment ready. Before the panels could go into the water, we had to prepare the equipment, rebuild the experimental frames and organize everything needed for the different parts of the experiment. Our setup consisted of large rectangular frames made from PVC pipes that carried the 15 x 15 cm settlement panels while they were in the water. In addition to this, we had speakers for the sound playbacks and ropes, buoys and weights that kept everything in position.
Although, there were frames left from a previous GAME project that was done in Cádiz, we decided to build new ones, which meant sourcing new material, cutting and assembling PVC pipes, preparing the panels and putting the different parts of the setup together. Some materials were bought locally, while others had to be ordered. This also resulted in one of our first small fieldwork adventures: transporting several metres of PVC pipes in a public transport bus through Cádiz was not exactly an everyday activity. We did not have a car at the time, and the large hardware store, where we bought some of the material, was quite far away, so getting everything back to Cádiz meant taking several buses while carrying long PVC pipes through crowded streets and vehicles. We bumped into things more than once, attracted a fair amount of attention and quickly realized that carrying several metres of PVC through a busy city is not as easy as it sounds. At one point, the combination of researchers, long PVC pipes and a local hardware store became what we jokingly refer to as the “Bus Hardware Store” episode.
Building the frames also taught us quite quickly that fieldwork rarely goes exactly according to plan. Some parts required a bit of improvisation and technical problem-solving, and when we reached a particularly stubborn technical issue, we even called Liam’s father in Germany for some additional advice. Although he was not directly involved in the project, his background in mechanical engineering and his experience with practical technical problems made him a useful person to call when we needed another perspective. A video call across Europe was not exactly part of the original plan, but it turned out to be a useful addition to our fieldwork toolkit.
At the same time as we worked on the set up, we were preparing the recordings of natural underwater soundscapes that would later be used for the experiment. For this, we built a deployment system consisting of a concrete-filled bucket, a wooden pole and a HydroMoth attached to the pole. The idea was simple: the heavy bucket keeps the structure stable on the seafloor, while the hydrophone records the surrounding natural soundscape above it. The practical part was considerably less simple. Several heavy loads of concrete had to be transported through Cádiz, and once the equipment reached the beach, getting the concrete-filled bucket into position was another workout altogether. We used a two-wheeled hand truck to move the heavy bucket across the beach and then into the shallow water. From there, we worked our way out by snorkeling and swimming, carrying and guiding the setup into position. The water was no more than about two metres deep, so there was no need for a boat.
The setup may have looked a little unconventional, but it was based on the plans we deleoped for recording natural soundscapes during the preparative course in March. After plenty of cutting, drilling, tying, carrying and assembling, the first major pieces of the project were finally ready. The frames were taking shape, the equipment was coming together and our first soundscape recordings were underway.
With the construction phase coming to an end, there was only one major question left: where exactly will we put everything?
When the plan changed
Finding a suitable experimental site turned out to be one of the more complicated parts of the project.
Our original plans involved a site in a nearby marina, but the situation changed when we were informed that construction work was planned close to the site. The associated noise would have interfered with the acoustic conditions required for our experiment, making the location unsuitable for our setup. We therefore had to move the experiment to a different location at relatively short notice. This meant adapting the setup and transporting the frames again. In the end, we found our new home at Puerto América, at the north-eastern tip of the city.
The change was a good example of how fieldwork can sometimes require a little flexibility. You can spend weeks discussing the experimental design, the set up and the site selection, but once you actually arrive at the water, there are always things that you could not have predicted from a map.
The new location gave us enough space for the experimental setup and allowed us to continue with the project. Hence, the frames were finally transported to Puerto América, weighted and installed.
Getting the frames into the water was actually much easier than building them in the first place. Once we had transported the frames to the harbour, we were able to get them into position and secure them relatively smoothly. The real challenge had been the preparation on beforehand: assembling the large PVC structures, attaching all the necessary components and making sure that everything was ready for deployment.
After weeks of preparation, the frames were finally in the water. The structures that we had spent so much time building on land were now ready to become the basis of our experiment.
From this point on, the focus shifted from building the experiment to monitoring what was happening around it.
Hydrophones, boats and one very expensive swim
Once the experiment was running, the HydroMoths became an important part of our regular monitoring. These small underwater recorders allowed us to record the acoustic conditions around our experimental frames and to measure the sound levels reaching the area of the experiment. This helped us to keep track of the underwater soundscape throughout the experimental period and to verify in hindcast what acoustic conditions the organisms on the settlement panels were actually exposed to.
Of course, regular monitorings also meant regularly getting the equipment in and out of the water. And this was when one of our more memorable fieldwork incidents happened. One day, Liam was alone at the harbour and had a fairly straightforward task: retrieve a HydroMoth, download the data and put it back into the water. Everything went well until the moment when the HydroMoth decided to make the last part of the procedure considerably easier for itself.
It slipped out of his hands and disappeared into the water.
We tried to retrieve it by diving down, but the visibility was extremely poor. Finding a relatively small piece of equipment underwater turned out to be much harder than expected, and despite our efforts, we could not recover it. It was certainly not part of the original plan, but fortunately, the experiment could continue. The lost HydroMoth has since become one of those fieldwork stories that is much easier to laugh about afterwards.
The regular monitorings also revealed how quickly conditions around the experimental site can change. One day, for example, we arrived at the harbour and found a boat parked remarkably close to our experimental setup, almost directly next to our buoys. Luckily, nothing was damaged and the boat did not cause any problems for the frames, but it was certainly an unexpected sight when we arrived.
Working in a harbour means that we are sharing the space with many other users, and sometimes the surroundings have a few surprises in store for us. Fortunately, most of them have been harmless so far.
From PVC panels to marine communities
The most interesting changes, however, did not happen above the water.
They happened on the settlement panels.
At the beginning of the experiment, the panels were simply pieces of PVC. We sanded their surfaces and standardized them so that they would provide suitable settlement substrates for marine sessile organisms. After deployment, there was not much to see.
Then the first organisms started to arrive.
During the first sampling events, we began to see the panels changing. Small organisms had settled on the surfaces, and the communities became increasingly diverse. Ascidians and bryozoans were among those colonizers that became particularly noticeable, together with worms, crustaceans and algae.
Suddenly, the panels that we had spent weeks preparing were becoming real pieces of habitat.
That was probably one of the most rewarding moments of the project. You knew exactly what a panel looked like before it went into the water. Then you retrieve it a few weeks later and had to figure out what has colonized it.
Some organisms were relatively easy to recognize. Others required a microscope, identification guides and considerably more patience.
Our supervisor was a huge help with this part of the project, especially when it came to identifying organisms that were less obvious at first glance. What initially looked like a small patch of something growing on a panel, could turn out to be an entirely different taxonomic group once you took a closer look.
And sometimes the organisms were simply fascinating to look at.
Despite the fauna and flora on the panels, we encountered small crustaceans, fish and other animals using the experimental structures as a habitat. One particularly photogenic shrimp even ended up on Liam’s hand during sampling.
The panels were therefore becoming more than just experimental units. They were small snapshots of the underwater world and the marine biodiversity around Cádiz.
The scientific question remained whether the different acoustic conditions influence the development of the communities. But before we could answer that, we had to document what was actually there.
And that meant sampling.
Sampling in the field
Our first sampling event made another aspect of fieldwork very clear: sometimes there is no perfect laboratory waiting for you at the harbour.
Since our experimental site was relatively far from the university facilities, we transported the equipment we needed directly to the field site by car. This included the microscope and the other equipment needed to examine, photograph and document the settlement panels.
There was no perfect laboratory waiting for us at the harbour. So, we built one.
We set up a small temporary workspace close to the experimental site and arranged everything we needed for the sampling. With the microscope, cameras, laptops, sampling equipment and the panels themselves, we quickly had our own little field laboratory ready to go.
Once everything was set up, the panels came out of the water. One by one, they were photographed, examined and assessed for the organisms that had settled on their surfaces. Some could be identified relatively easily, while others required a closer look under the microscope and a little more time.
The same basic procedure was repeated during the following sampling event, allowing us to compare how the panels had changed over time and which organisms had newly appeared or become more abundant.
Working directly at the field site also had its advantages. Instead of transporting the panels back and forth, we could examine and document them close to where the experiment was running and get an immediate impression of how the communities were developing.
Of course, the conditions were not always perfectly calm. Strong winds can make working at the harbour considerably more challenging, and this is where we really began to appreciate the Levante, the strong easterly wind that regularly affects the Cádiz area. By