Short-Term Microplastic Exposure Impairs Cognition in Hermit Crabs.

We tested whether acute microplastic exposure impacts information gathering and processing (cognition) in hermit crabs ( Pagurus bernhardus ). For five days, we kept 51 hermit crabs in tanks containing either polyethylene microspheres ( n = 27) or no plastic ( n = 24). We then transferred individuals into an intermediate-quality shell and presented them with two vials containing either a better or worse shell. Because touching both shell vials required an equivalent behavioural response, this design controlled for general activity. Plastic-exposed hermit crabs were less likely and slower than controls to touch the better shell vial, instead preferring the worse shell vial. Microplastics, therefore, impaired assessments and decision-making, providing direct evidence of acute microplastic exposure disrupting hermit crab cognition.