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An oceanic mystery has unfolded with the discovery of a large crab inside a plastic bottle, with an opening far too small for the crustacean to have fit through.
The seemingly impossible discovery, made by researchers with Hiroshima University, has now revealed a new dimension to the effects of pollution in our environment, and how plastic objects can have unexpected impacts on ocean creatures.
The researchers made the curious discovery off the coast of Okinawa, Japan. Upon discovering a polyethylene Shaoxing wine bottle drifting along on the ocean surface, they soon realized that the discarded plastic container was thriving with signs of life.
Most peculiar of all was the presence of a large swimming crab within the bottle, which was obviously too have made its way inside the container through its narrow opening.
“During juvenile fish surveys in offshore waters, we happened to encounter a floating plastic bottle approximately 500 meters (about 550 yards) off Sesoko Island, Okinawa, Japan, with many juvenile fish associated with it,” said Hajime Sato and Yoichi Sakai, the authors of a new study describing the discovery.
According to Sato, “a large live swimming crab, Portunus sanguinolentus, was trapped inside the bottle.”
“The crab was clearly larger than the opening of the bottle!” Sato said.
In the image above, the bottle (left) can be seen alongside the crab and several juvenile fish collected around the time of the discovery (Image Credit: Hajime Sato / Hiroshima University)
The Marine Plastic Problem
It is no secret that plastic has been a longtime contributor to pollution in Earth’s oceans, with wide-ranging impacts on oceanic environments that include ocean creatures becoming ensnared in discarded plastic bags, dishing nets, or other plastic refuse.
Sato and Sakai say the plastic bottle they collected in July 2022 had been manufactured the previous November, and had been left uncapped, allowing seawater to enter and leave. However, it was clear that the crab they discovered within it could not have made its way in as easily as the ocean water it contained.
Unraveling this oceanic mystery required an array of biological analyses, which ultimately led them to a striking conclusion: the crab had entered the bottle when it was far smaller, and remained there, subsisting on organisms and other food sources making their way into the small plastic vessel, allowing it to grow as the bottle drifted along.
Based on DNA analysis of the crab’s stomach contents, the crustacean had recently consumed juvenile fish that entered the bottle, including specimens of the rough triggerfish Canthidermis maculate. Additional analysis also revealed the presence of the sergeant major Abudefduf vaigiensis.
Evidence of algae within the bottle indicated another likely food source for the crab, while on the bottle’s exterior, goose barnacle growth revealed the likely time the bottle must have spent drifting for these oceanic hitchhikers to become attached and grow.
The most likely scenario, according to Sato and Sakai, is that the young crab entered the bottle, where it fed on juvenile fish and algae over the course of two months, eventually growing large enough that it could no longer escape.
“Plastic bottles discarded by humans can trap crabs and prevent their escape,” the authors conclude, adding that “Similar cases have already been reported from waters around Japan, suggesting that this was not an isolated accident.”
“Through this striking example, we would like readers to recognize that objects that make our lives more convenient can sometimes have unexpected effects on small marine animals,” Sato and Sakai add, “while also appreciating the remarkable vitality of the swimming crab,” the authors conclude.
The unusual discovery was detailed in a recent study, “Swimming crab in a bottle: A two‐month drift on the ocean surface while entrapped,” which appeared in the journal Ecosphere.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached atmicah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.
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Over 20 million tons of polystyrene plastic are produced annually, yet only a small fraction is recycled worldwide. Current recycling methods consume large amounts of energy and often rely on harsh and toxic chemicals to break the strong molecular chains that make up polystyrene. One possible solution is the use of sulfur, which is an inexpensive byproduct formed when refining crude oil. Its unique chemical structure allows it to break up strong chemical chains in long plastic molecules. Despite its abundance, sulfur has very limited applications, and converting it into more usable forms tends to require a lot of heat, rendering it unused for long periods of time.
Researchers at the Dalian Institute of Chemical Physics hypothesized that sulfur could help break down polystyrene waste to form more valuable chemicals. To power this reaction, they converted sunlight into heat energy through a process called photothermalconversion. They used this heat to transform polystyrene and sulfur into valuable chemicals like 2,4-diphenylthiophene, or chemical D, and 1,3,5-triphenylbenzene, or chemical T, which are used to make semiconductors and chemical sensors.
To test this, the team mixed ground polystyrene and sulfur at a molar ratio of 1:0.5 in a glass test tube. They sealed the tube with a balloon and secured it onto an iron stand. Then, they focused sunlight onto the bottom of the tube using a curved mirror. As the mixture heated up, the yellow-white solids gradually melted and transformed into a reddish-black liquid after 2 minutes. After heating, the researchers removed the mirror and allowed the system to cool before collecting the gaseous products from the balloon and dissolving the remaining solids for further purification and analysis.
The researchers then adjusted the reaction conditions to understand what factors influenced their results. They tested the reaction without sulfur, varied the sulfur ratios from 0.2 to 0.8, and replaced elemental sulfur with other sulfur-containing compounds. They also explored adding known photothermal agents, specifically metal oxide additives, to the mixture.
To compare the difference between sunlight and artificial light, the researchers repeated the experiment indoors using a 100 Watt LED bulb and monitored temperature changes with a thermal camera. They also ran a control experiment using only polystyrene to check how sulfur affected the yield under LED light. They also tested exposure times from 1 to 6 minutes in 1-minute increments to determine how long it took to achieve the highest yields under LED. The researchers used these tests to identify which conditions were necessary for the reaction to occur and how different factors influenced its outcome.
They found that without sulfur or with alternative sulfur-containing compounds, the reaction did not produce chemical D or T under sunlight. In contrast, reactions that included sulfur successfully produced these target products, with the highest yields of 34% for D and 16% for T at a sulfur ratio of 0.5. When they added metal oxides, the chemical yields decreased to 22% and 12%, respectively, suggesting that these additives interfered with the desired reactions. In addition, when the researchers switched from sunlight to LED, the reaction yields dropped to 26% for D and 13% for T.
Next, they examined how reaction time influenced product formation. They found that yields increased gradually before reaching the maximum at 4 minutes and leveling off. They also noted that mixtures containing sulfur heated up from room temperature to 320°C (608°F), while the control setup only showed a slight temperature increase. The researchers interpreted these results as confirmation of sulfur’s dual role as a reactant and a light-to-heat converter that enables the conversion of polystyrene to useful chemicals.
Taking it a step further, the researchers tested their method on real-world polystyrene wastes, including food packaging, cup lids, and foamed plastics. They successfully produced chemicals D and T from these materials, demonstrating that their process works beyond laboratory samples.
The team concluded that their study presents a simple, fast, and solvent-free approach to converting 2 abundant waste materials into valuable chemicals using sunlight. By combining polystyrene waste and excess sulfur, the researchers offer a new pathway for sustainable polymer upcycling that uses clean energy and is broadly applicable to everyday plastics.
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