Abandoned tires dumped into the ocean are turning into deadly traps for hermit crabs, who may be resorting to eating each other in a desperate but futile gambit to survive.
According to a study out of Japan's Hirosaki University, the bottom-feeding arthropods can crawl into a tire's concave interior but can't get out.
Biologists Atsushi Sogabe and Kiichi Takatsuji found hundreds of hermit crab shells inside a discarded tire in Aomori Prefecture's Mutsu Bay.
Some still had occupants but many more were damaged and discarded—a sign, Sogabe and Takatsuji believed, that the crab inside had fallen victim to cannibalism or violent competition for food or shelter.
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Tires discarded in the ocean are becoming deadly traps for hermit crabs, who can climb into the concave structures but can't get out. Over a period of a year, researchers counted nearly 1,300 crabs stuck inside six tires in Mutsu Bay
To test their theory, they submerged six car tires about 25 feet deep in various locations in the bay and came back once a month to see if they had entrapped any hermit crabs.
Over the course of a year, they counted 1,278 hermit crabs within the six tires.
At each monthly interval, Sogabe and Takatsuji said, they released any trapped crabs more than 160 feet from any of the tires.
If they hadn't, the crustaceans surely would have died from starvation or cannibalism, they said.
The severe damage done to discarded shells (above) suggests the inhabitants were caught in violent struggles for food and shelter, and may have even been eaten by other crabs
In a separate experiment, Sogabe and Takatsuji also placed a car tire in a large aquarium and added hermit crabs—some inside the tire, some outside.
Over six trials, each lasting 18 hours, they confirmed the crabs could climb into the wheel, but not out of it.
Hermit crabs live in scavenged sea snail shells and when they die, they release a chemical signal to others of their species that a home is available.
This attracts more crabs into the rubbish that trapped them.
Hermit crabs play an important role in marine ecosystems, both as prey for larger animals like shorebirds and as scavengers that keep the seabed clean and turn and circulate soil, helping plants to grow
Marine life can often get caught in discarded fishing nets and other ocean litter, a phenomenon known as 'ghost fishing.'
However, tires are an even deadlier danger than nets, Sogabe and Takatsuji note.
'The length of time that fishing gear can ghost fish ranges from a few months to three years, depending on gear type, what it is made of, and the environment into which it was discarded,' the researchers wrote in a report published in the journal Royal Society Open Science.
'Because of their simple structure, temporal persistence and robustness, tires may ghost fish hermit crabs for considerably longer.'
Hermit crabs play an important role in marine ecosystems, both as prey for larger animals like shorebirds, and as scavengers that keep the seabed clean and turn and circulate soil,
