It’s been found that discarded tires lying on the seabed are death traps for hermit crabs. They climb into the tyres but can’t get out because the walls are concave. It’s as simple as that. I suppose they climb into them for protection but it becomes a cage which they can’t get out of. Hirosaki University biologists Atsushi Sogabe and Kiichi Takatsuji conducted two tests, one in the sea and a second in a test environment using an aquarium to confirm whether crabs could enter and then be trapped inside a tyre. They placed a tyre and a large tank with a sandy bottom.
They added hermit crabs from the most common species that they had observed in the field. Over six trials each lasting 18 hours they found that hermit crabs could climb into the tyre but couldn’t get out. The outside of a tyre is convex but the inside is concave and it is that simple physical difference between inside and outside which trapped them.
They described the process as ghost fishing. Ghost fishing is when marine wildlife becomes trapped in discarded nets and other Fishing gear. But they say that tyres can be worse because tyres last longer under the sea. They say that tyres have a “temporal persistence”. This is scientific language to mean that they last a long time!
Hermit crabs are important to the ecosystem in that they are both prey and scavengers. The ghost fishing of hermit crabs can have a cascading effect on coastal communities and ecosystems.
The source of this article is Real Clear Science and they refer to the following: Sogabe Atsushi and Takatsuji Kiichi 2021 “Marine-dumped waste tyres cause the ghost fishing of hermit crabs.” R. Soc. open sci. 8210166210166 http://doi.org/10.1098/rsos.210166.
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