Caddisfly larvae (Trichoptera: Limnephilidae) facilitate the uptake of microplastics by a freshwater fish (Ameiurus nebulosus)

Abstract

Microplastics are pervasive in inland waters and are entering aquatic food webs through diverse pathways. Caddisflies (Trichoptera) are common prey items for fishes and some aquatic birds; they have been found to incorporate microplastic particles in their larval cases, which are a potential vector of plastic transmission to higher trophic levels. We examined this novel pathway in two sets of experiments. First, we exposed caseless Limnephilus larvae to either i) a 50% mixture of polyethylene terephthalate (PET) microfragments and natural materials, or ii) 100% natural materials, and compared their subsequent case construction. Limnephilus consistently incorporated PET into their cases, even when natural material was available. However, only 5% of larvae constructed a case completely covering the abdominal region of their body when they used PET fragments. Cases incorporating plastic had a lower mass than those constructed entirely from natural materials, regardless of the mass of the larvae. These findings suggest that the incorporation of microplastics affects case structure and, potentially, functionality. In a subsequent set of experiments, we offered four partially plastic-cased and four natural-cased caddisfly larvae to a benthivorous fish, the brown bullhead (Ameiurus nebulosus). Ninety percent (9/10) of the bullheads selected a larva with plastic in its case over a larva with a fully natural case as the first prey they attacked. Overall, consumption of plastic-cased larvae represented 63% of all prey consumed, suggesting that the incorporation of PET microplastic fragments in case matrices renders larval caddisflies more vulnerable to predation. Case-building caddisflies can thus facilitate the transfer of plastic and associated contaminants into aquatic food webs.