No, Hermit Crabs Aren't Hot For Plastic, Some Shrimps On The Other Hand...

While hermit crabs are prone to nibbling on plastic pollution, that's as far as the attraction goes. Image credit: Tiphat Banjongpru

You might have seen a few saucy headlines floating around kink-shaming hermit crabs for being sexually attracted to ocean plastic (possibly due to a wee press office snafu involving a paper about horny shrimp – more on that later), but the reality painted by a recent piece of research is slightly different. The UK-based study looked at the behavior of hermit crabs when exposed to increased concentrations of oleamide, a contaminant that can leach from plastic pollution, and found that hermit crabs were attracted to its scent and would even try and nibble on plastic, increasing their risk of ingesting this unnatural material.

Published in the Marine Pollution Bulletin, the study outlined how additive leaching could be playing a significant role in drawing marine life towards plastic. “The work is part of a research cluster on the impacts of stress on marine life and my research team working on odor/smell/olfaction as a means of communication and the impacts climate change as well as toxic compounds (i.e. from plastic) have upon this means of communication, often referred to as the language of life,” said corresponding author Dr Jorg D Hardege to IFLScience.

The specific chemical in question in this new research was the plastic additive oleamide (9-octadecenamide), which when exposed to hermit crabs (Pagurus bernhardus) was found to increase their respiration rate even in low concentrations.

Far from thinking with their genitals, the attraction exhibited by the “hungry for plastic” crabs was found to mimic that observed when they are exposed to the feeding stimulant betaine. So, what is it about oleamide that these hermits find so appetizing?

The chemical characteristics of oleamide are very similar to that of an acid released by decomposing arthropods and algae. Hermit crabs are scavengers which means they comb the seafloor looking for nice dead stuff to feast upon. It would perhaps stand to reason, then, that they would be attracted to something that mimics the chemical cues of a manky old lobster that’s ripe for the picking. The researchers suggest that this could present an “olfactory trap” for the hermit crabs, who are a slave to their food cravings.

The situation is different, however, when it comes to the hermaphroditic shrimp Lysmata boggessi. In a separate paper published in the journal Plos One back in 2011, researchers tested the hypothesis that oleamides acted like sexual cues for the shrimps as they shared characteristics with pheromones found on the female’s body that are also found on insects and event pandas. If true, it could indicate that ocean plastic presents a seductive obstacle between shrimp mating with actual shrimp.

Their results demonstrated that oleamide was a pivotal ingredient for romantic interest, with hexadecanamide and methyl linoleate enhancing the pheromone’s allure. The study demonstrates that pheromone cues appear to exist in aquatic systems, and if oleamides are leaching from ocean plastic they could well be getting shrimps hot under the collar as they attempt to mate with human trash.

"The original 2011 paper he showed that if you put Oleamide onto a small object then male shrimps will treat this as beign a female – whether sufficient quantities of Oleamide leach out of lets say polyethylene tubes to induce that I don't know, it's worth a study really and maybe something we test this autumn," explained Hardege. "So really, Oleamide is a sex cue in shrimps and when added to hermit crabs they get exited and explore as if it is food. As Oleamide occurs naturally and is chemically very similar to a compound leaching out of decomposing algae, that makes sense."

“We now try to examine what the long term effects are – do hermit crabs suffer and go hungry if they mistake plastic for food? What happens if they eat and incorporate this? Is this sort of mistaking plastic for food or as a sexual cue in the shrimps something widespread in marine life? We then combine this with our climate change research to see if the acidification of the oceans due to increasing CO2 means that these chemicals get worse or better,” Hardege told IFLScience.


 This Week in IFLScience

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