Accumulation of marine microplastics along a trophic gradient as determined by an Agent-Based Model.

Abstract

Microplastics are ubiquitous in the marine environment and are now consistently found in almost all marine animals. This study examines the rate of accumulation in a modelled filter feeder (mussels) both from direct uptake of microplastics and from direct uptake in addition to trophic uptake (via consuming plankton which have consumed microplastic themselves). We show that trophic uptake plays an important role in increasing plastic present in filter feeders, especially when consumption of the plastic does not reduce its overall abundance in the water column (e.g. in areas with high water flow such as estuaries). However, we also show that trophic transfer increases microplastic uptake, even if the amount of plastic is limited and depleted, as long as plankton are able to reproduce (for example, as would happen during a plankton bloom). If both plankton and plastic are limited and reduced in concentration by filter feeding, then no increase in microplastic by trophic transfer occurs, but microplastic still enters the filter feeders. The results have important implications for large filter feeders such as baleen whales, basking and whale sharks, as these animals concentrate their feeding on zooplankton blooms and as a result are likely to consume more plastic than previous studies have predicted.