Abstract
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.