Microplastic Ingestion by a Benthic Amphipod in Different Feeding Modes

Abstract

Microplastics adversely affect organisms through physical damage, inhibition of food assimilation, and/or toxicity of chemical leachates. We investigated the influence of feeding mode on microplastic ingestion by using polystyrene microbeads (diameter: 4.1 and 20.6 μm) and the estuarine benthic amphipod Grandidierella japonica, which can switch between filter-feeding and deposit-feeding modes. When provided with sediment, amphipods burrowed and were in the filter-feeding mode; they ingested 4.1 and 20.6 μm beads in the ratio at which the two sizes were suspended in the water. Without sediment, however, the amphipods were mainly in the deposit-feeding mode and ingested more 20.6 μm beads, which tended to be deposited on the bottom, compared with 4.1 μm beads. In addition, the number of microbeads ingested by the amphipods in sediment increased as the amount of food provided (i.e., fish food TetraMin) increased, whereas no such increase was observed for the amphipods without sediment. These results indicate that the microbead ingestion was dependent on feeding mode (i.e., presence/absence of sediment), amount of food, and distribution of microbeads (i.e., sizes of microbeads). To better understand the ingestion, accumulation, and toxicity of microplastics in aquatic environments, we recommend that more attention be paid to behavioral changes in benthic organisms.