Jellyfish And Plastic Pollution: Understanding The Impact

Plastic pollution is a pressing issue, with 14 million tons of plastic entering the sea each year. While plastic pollution is harmful to most marine life, jellyfish are able to survive and even thrive in environments with high levels of plastic pollution. In fact, jellyfish have been found to ingest plastic, and their mucus has been found to be an effective way to filter microplastics from the ocean.

Jellyfish ingest plastic, mistaking it for food

Jellyfish do ingest plastic, mistaking it for food. In 2018, a study published in the journal Scientific Reports provided the first documentation of plastic in a jellyfish. The study, conducted by scientists participating in the Aquatilis Expedition, found that out of twenty mauve stingers (Pelagia noctiluca) netted and inspected, four had plastic in their digestive systems. The researchers believed that the jellyfish had mistaken the plastic for food.

Mauve stingers are considered opportunistic predators, feeding on zooplankton of varying sizes and types as an adaptive strategy in the open ocean. This makes them particularly vulnerable to ingesting plastic, as they consume a wide range of prey. Additionally, the dispersal of this species is heavily influenced by local winds and currents, which tend to concentrate them in regions with high levels of floating litter.

The ingestion of plastic by jellyfish can have detrimental effects on their health. Mauve stingers, for example, can consume prey equivalent to more than 50% of their body weight per day. Ingesting large amounts of plastic can lead to gut blockage, reduced energy reserves, and starvation. It can also expose them to toxic substances adsorbed onto the plastic surface or leached from the polymer matrix, such as phthalates and flame retardants.

Furthermore, as jellyfish are a key food source for pelagic top predators, the consumption of plastic by jellyfish can have indirect effects on other species in the marine food chain. Bluefin tuna, for example, is known to prey on mauve stingers, and plastic consumed by the jellyfish may end up in the bellies of larger species, including humans.

While the exact reasons why jellyfish are attracted to plastic are not fully understood, it is hypothesized that the presence of marine litter in their gastrovascular cavity is due to the visual, tactile, or olfactory misidentification of plastic as prey. For example, algae can easily grow on ocean plastic, and as it breaks down, it emits an odor called dimethyl sulfide (DMS) that attracts hungry animals. DMS is produced by krill, a primary food source for many seabirds, and the smell can lead them to mistake plastic for food.

Plastic in the ocean can smell appetising to jellyfish

Marine animals, including jellyfish, are consuming alarming amounts of plastic. While it was previously thought that they were simply mistaking plastic for prey, recent studies have found that there is another reason for this behaviour: the plastic smells appetising.

In 2016, a study in the journal Science Advances found that algae easily grows on ocean plastic. As the algae break down, they emit an odour called dimethyl sulfide (DMS). This odour attracts hungry animals, as it signals the presence of food. Sea birds, for example, associate the smell of DMS with their primary food source, krill.

Similarly, sea turtles have been found to respond to the scent of biofouled plastics (plastics with an accumulation of microbes, algae, plants, and small animals on their surfaces) in the same way they respond to food odours. This suggests that, like seabirds, they are attracted to plastic debris not only by the way it looks but also by the way it smells.

While it is not entirely clear why jellyfish are attracted to plastic, Armando Macali, an ecologist from Tuscia University in Italy, suspects that either the biofilm or some molecule in the breaking-down plastic is the attracting factor.

Plastic provides a surface for jellyfish to attach to and thrive

Plastic pollution has been found to be beneficial to jellyfish, which have been described as "thriving" due to the presence of plastics in the ocean.

Jellyfish have a complex lifecycle, and during their "polyp" phase, they must attach themselves to a surface in order to grow. In natural circumstances, jellyfish polyps settle on the ocean floor. However, with the presence of plastics in the ocean, jellyfish have been provided with alternative surfaces to attach to. This has allowed jellyfish to thrive in deeper waters, no longer needing to remain in coastal areas or endure great depths to find a suitable substrate. As a result, jellyfish populations and range have expanded.

Jellyfish are highly opportunistic and adaptable, and they have survived every mass extinction in Earth's history since their evolution. They are boneless, so pH imbalances in the ocean do not affect them in the same way as marine species with skeletal structures. Jellyfish are also able to tolerate rising ocean temperatures, which negatively impact other species, allowing jellyfish to outcompete their adversaries for food.

The presence of plastics in the ocean has also been found to indirectly benefit jellyfish populations. Plastics provide a surface for algae to grow, and as the algae break down, they emit an odor called dimethyl sulfide that attracts hungry jellyfish.

While jellyfish populations may benefit from plastic pollution in the short term, it is important to note that plastics can still pose a threat to jellyfish through ingestion and entanglement. Additionally, the overall health of marine ecosystems, including jellyfish, is threatened by the presence of plastics and other forms of pollution.

Jellyfish mucus can be used to filter microplastics from water

The GoJelly project, funded by the European Union, aims to use this property of jellyfish mucus to create filters that can be used in wastewater treatment plants and factories where microplastics are produced. The project is currently in the process of testing various plastic particles and harvesting jellyfish from the sea. The mucus will be integrated into the filter, which will then be tested and demonstrated in the Norwegian, Baltic, and Mediterranean Seas.

The use of jellyfish mucus as a filter for microplastics is a nature-based solution that addresses two problems: the proliferation of jellyfish, and microplastic waste in the world's oceans. Jellyfish blooms, favoured by rising water temperatures, ocean acidity, and overfishing, have an adverse impact on tourism, aquaculture, and fishing industries. By using jellyfish mucus to filter microplastics, the GoJelly project aims to reduce the number of jellyfish and, consequently, the problems they cause.

The process of collecting and storing jellyfish mucus is challenging, and the project faces hurdles such as the seasonal and regional variability in the availability of jellyfish and the need for rapid and efficient biomaterial processing and storage. However, the project holds promise as a potential solution to the global issue of microplastic pollution.

Plastic pollution can cause jellyfish populations to increase

Jellyfish are also able to use plastic pollution to their advantage during some critical stages of their formation. In their early lives, jellyfish float along with the tides as tiny larvae. During this stage, they must attach themselves to a surface in order to grow. Usually, they settle into the ocean floor, but with an influx of plastics in the ocean, they are provided with more surfaces to attach to. This means jellyfish can thrive in deeper water, no longer needing to remain on coastlines or endure great depths to reach a substrate. This has allowed jellyfish populations to expand and their range to increase.

In addition, ocean plastic can smell appetising to some marine creatures, including jellyfish. Algae easily grows on ocean plastic, and as it breaks down, it emits an odour called dimethyl sulfide that attracts hungry animals. This means that jellyfish are more likely to ingest plastic, mistaking it for food. This can cause health issues for jellyfish, but it also means they are ingesting more plastic than they would be without plastic pollution, which can help them survive.

Jellyfish are also able to use their mucus to their advantage in a plastic-polluted ocean. Jellyfish produce copious amounts of mucus, which can be used to trap microplastics. This is useful for combatting plastic pollution, but it also means that jellyfish can more easily rid themselves of the plastic they ingest.

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