Plastic additive oleamide elicits hyperactivity in hermit crabs

Highlights: • The plastic additive oleamide is a known signalling molecule present in the animal kingdom as olfactory chemical signal. • Oxygen consumption in hermit crabs (Pagurus bernhardus) increases significantly in response to oleamide. • Hermit crabs are attracted to low concentrations of oleamide in a manner comparable to the feeding stimulant betaine. • Oleamide may be perceived as a feeding cue by marine species potentially increasing the consumption of microplastics. Numerous studies have estimated the abundance of plastics in our oceans and warned of its threat to wildlife. However, mechanisms underlying its attractiveness to marine life remain unclear. Though visual similarities to food sources have been suggested, recent studies show that biofouled plastics release dimethyl sulfide which marine fauna mistake for food whilst foraging. Our study shows that the plastic additive oleamide (9-octadecenamide) attracts hermit crabs (Pagurus bernhardus). Respiration rate increases significantly in response to low concentrations of oleamide, and hermit crabs show a behavioral attraction comparable to their response to the feeding stimulant betaine. Oleamide has a striking resemblance to the necromone oleic acid, a chemical released by arthropods during decomposition. As scavengers, hermit crabs may misidentify oleamide as a food source, creating an olfactory trap. As such, our short communication demonstrates that additive leaching may play a significant role in the attraction of marine life to plastic.