Effects of temperature and microplastic concentration on the consumption of microplastic particles by the detritivore Asellus aquaticus

Abstract: Microplastic (MP) pollution has now reached a point where particles can be found in every environmental compartment across the globe. However, the ecological and long-term consequences of MPs are largely unknown. These particles are expected to impact many organisms through ingestion, with organisms feeding off particles and detritus predicted to be especially heavily affected. Using the model detritivore Asellus aquaticus (Crustacea: Isopoda), the ingestion of MP particles at 3 different temperatures and 3 MP concentrations was investigated, by quantifying the number of MP particles excreted in the animal's faecal matter. I predicted that (i) MP numbers in A.aquaticus faecal particles would increase with MP concentration, (ii) MP particle numbers would increase with temperature, (iii) A. aquaticus start biomass would not differ between treatments, (iiii) A. aquaticus final biomass will not differ from the start biomass, (iiiii) survivorship of A. aquaticus will be lower at warmer temperatures and higher MP concentrations, (iiiiii) Increased shedding rates in high temperatures and MP concentrations. The collected data was analysed by dying the samples using Nile Red and counting the MP particles found in the faeces of the animals for each microcosm utilising a fluorescent microscope. An ANOVA analysis was then conducted. This study showed that temperature had no effect on the excrement of MP particles, the only factor of significance was the concentration of MPs in the microcosm. These findings indicate that A. aquaticus has little capacity to avoid consuming MPs, rather it is subject to ambient concentrations- the more MPs in the environment- the more it eats. This in turn implies that A. aquaticus faecal particles might be a key pathway for the further transfer of MPs in freshwater foodwebs, passed on to further consumers that eat faecal particles. Survivorship, start biomass and final biomass was also analyzed but showed results of no significance.