Hermit crabs are actually attracted to plastic additives

Hermit crabs may become sexually “excited” by an additive that is released from plastics in the ocean, according to a new study from the University of Hull.

The plastic additive oleamide is known to act as a pheromone that affects the behavior of certain marine animals, such as shrimp. 

The researchers, including PhD candidate Paula Schirrmacher, have been studying the compounding effects of marine plastic pollution and climate change on hermit crabs.

The experts found that oleamide increases the respiration rate of hermit crabs, signifying attraction and excitement. The substance can easily be mistaken for food. This means that hermit crabs may travel over a long distance in pursuit of a meal, only for the energy to be wasted on plastic. 

“Our study shows that oleamide attracts hermit crabs. Respiration rate increases significantly in response to low concentrations of oleamide, and hermit crabs show a behavioural attraction comparable to their response to a feeding stimulant,” said Schirrmacher.

“Oleamide also has a striking resemblance to oleic acid, a chemical released by arthropods during decomposition. As scavengers, hermit crabs may misidentify oleamide as a food source, creating a trap.”

“This research demonstrates that additive leaching may play a significant role in the attraction of marine life to plastic.”

Study co-author Luana Fiorella Mincarelli said that it is important to understand how plastic additives work on molecular levels, especially on reproductive success. “We have found that their toxic effect can be amplified in a climate change scenario.”

The research shows that male blue mussels were the most adversely affected by increased temperature, but females were more sensitive to DEHP, a toxic chemical found in many plastics.

The study authors concluded that rising ocean temperatures, combined with rising levels of plastic pollution, disrupt the breeding cycles of blue mussels and has a negative impact on their reproduction rates.

In another experiment, the team found evidence which confirms the theory that ocean acidification impairs the sense of smell of hermit crabs and other creatures, limiting their ability to communicate.

“Whether or not marine animals can smell plastics is a topic that previously attracted a lot of scientific controversy, but there was not much actual data,” said study co-author Dr. Jorg Hardege.

But now, Schirrmacher’s study on hermit crabs in Robin Hood’s Bay has revealed that the creatures are actually attracted to a chemical cue known as PEA (2-phenylethylamine). PEA is known to warn sea creatures of predators.

“To receive smell-related information correctly, the odor molecule needs to properly fit and bind to the receptor,” said Dr. Christina Roggatz.

“Our results show how lower environmental pH causes small changes in the chemical properties of the odour molecules, which in turn facilitate this crucial binding step. In short: pH can make or break successful communication in the ocean.”

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By Chrissy Sexton, Earth.com Staff Writer