Myriads of tiny plastic particles threaten marine ecosystems worldwide. A study once again documents how complex this environmental problem is: microplastics therefore impair the ability of hermit crabs to find a suitable snail shell as a home. This shows that the behavior of marine animals can also be affected by the particles, the scientists say.
A look at the beach goods on the coasts of the world makes it clear: The seas are heavily polluted with plastic waste. However, the large pieces are only part of a much more far-reaching problem: the oceans are teeming with tiny plastic particles that are less than five millimeters in size. Particles in care products can be a source of this microplastic, but most of all it is the remains of the decay of plastic products such as plastic bags and the like. In some areas of the sea, these tiny things can accumulate particularly intensely and threaten marine life. Some studies have already shown that ingestion creates dangers and that microplastics can also release harmful substances. The problem has dimensions that can only be guessed at so far, warn marine conservationists.
Complex environmental problem
The study by Andrew Crump’s researchers from Queen’s University Belfast is now part of the collection of information on the complex hazard potential of microplastics. The marine biologists have dealt with a creature that is known for its strange-looking behavior: the common hermit crab (Pagurus bernhardus) looks for empty snail shells as a dwelling and then uses them as a mobile shelter. On many coasts in Europe you can watch these journeyman animals, up to ten centimeters tall, crawling across the beach with their houses.
In the course of their development, moving is always necessary: ​​if the crabs grow, they need a larger snail shell. As the researchers explain, the animals are “careful” when looking for a home: They record the characteristics of available snail shells with their feelers and then decide for or against moving. The right choice is of great importance for the chances of survival of the crayfish, emphasize the researchers. As part of their study, they have now investigated the suspicion that exposure to microplastics can have an impact on this behavior.
For this purpose, they kept hermit crabs for five days in two different test tanks: one contained pure water, the other, however, was contaminated with microplastics. These were tiny polyethylene spheres with a concentration that can occur under real conditions in the animal’s habitat. After the incubation period, the scientists took the crabs out of their homes and transferred them to snail shells that were less than ideal for them. Then they were placed in observation boxes, in which they were provided with optimal mussel shells for moving.
Focus on moving behavior
As the scientists report, the behavioral analysis showed that, in contrast to the control animals, the hermit crabs that had previously been exposed to microplastics showed impairments when choosing a better dwelling: They examined the alternatives only reluctantly and were also less likely to move to an optimal house than your
Colleagues who had previously lived in unpolluted water. The researchers interpret the results as a sign that the microplastics have impaired the animals’ ability to collect or process information.
So far, however, they have not been able to say exactly what effect this effect is based on. This would have to clarify further investigations, write the scientists. However, it is possible that substances made of plastic have entered the animal’s nervous system after swallowing the particles and cause disturbances there. But it would also be possible that the absorption of particles creates a false feeling of satiety, which causes the crayfish’s energy balance to become confused and thus possibly also their behavior.
“We hope that further studies will now look into the effects of microplastic exposure on specific cognitive processes in marine animals,” the scientists conclude.