Behavioural Responses of Mussels to Natural and Synthetic Textile Microfibres and Their Leachates

Textile microfibres are pervasive anthropogenic debris in coastal ecosystems. Although their effects on marine organisms are increasingly documented, the relative effects of direct fibre exposure and fibre-derived leachates, and differences between natural and synthetic fibres, remain poorly understood. We experimentally tested how textile microfibres (MFs) and their leachates, from natural (cotton, wool) and synthetic (polyester, acrylic) sources, affect behavioural traits of the mussel Mytilus edulis, a coastal ecosystem engineer. After 24 h of exposure, no behavioural effects were detected at 10 MF L−1. At 1000 MF L−1, wool microfibres reduced attachment and byssal thread production. At 10,000 MF L−1, wool additionally impaired aggregation and movement, while acrylic mainly affected attachment and thread production. Leachate-only treatments produced no measurable behavioural effects, while direct fibre exposure altered behaviour at elevated concentrations. However, physical effects cannot be separated from those of fibre-associated chemicals or additives. These findings show that behavioural disruption depends on fibre concentration and composition, and that even natural fibres can impair mussel performance under elevated exposure conditions.