Ingestion and fragmentation of plastic carrier bags by the amphipod Orchestia gammarellus: Effects of plastic type and fouling load

Highlights: • An experimental study testing the effect of biofilms and plastic type on plastic bag biodegradation by O. gammarellus. • O. gammarellus shreds plastic carrier bags generating numerous pieces of microplastic (488.59 μm average diameter). • Fouling significantly increased the amount of plastic shredded producing an average 8.23 fragments/amphipod/day. • Plastic type had no effect on the amount shredded. • Subsequent field observations confirmed the shredding of plastic carrier-bags in the field. - Abstract: Inappropriate disposal of plastic debris has led to the contamination of marine habitats worldwide. This debris can be ingested by organisms; however, the extent to which chewing and gut transit modifies plastic debris is unclear. Detritivores, such as amphipods, ingest and shred natural organic matter and are fundamental to its breakdown. Here we examine ingestion and shredding of plastic carrier bags by Orchestia gammarellus. A laboratory experiment showed these amphipods shredded plastic carrier bags, generating numerous microplastic fragments (average diameter 488.59 μm). The presence of a biofilm significantly increased the amount of shredding, but plastic type (conventional, degradable and biodegradable) had no effect. Subsequent field observations confirmed similar shredding occurred on the strandline. Rates of shredding will vary according to amphipod density; however, our data indicates that shredding by organisms could substantially accelerate the formation microplastics in the environment.