The effects of microplastic on freshwater Hydra attenuata feeding, morphology & reproduction

Microplastic pollution has been a growing concern in the aquatic environment for several years. The abundance of microplastics in the environment has invariably led them to interact with a variety of different aquatic species. The small size of microplastics may make them bioavailable to a great range of species however, the impact this may have is not fully understood. Much of the research on microplastic pollution has focused on the marine environment and species with little research undertaken in freshwater. Here we examine the effect of microplastics on the freshwater cnidarian, Hydra attenuata. This study also describes the development and use of a bioassay to investigate the impact of microplastic on freshwater organisms. Hydra attenuata play a vital role in the planktonic make up of slow moving freshwater bodies which they inhabit and are sensitive environmental indicators. Hydra attenuata were exposed to polyethylene flakes (< 400 μm) extracted from facewash at different concentrations (Control, 0.01, 0.02, 0.04, 0.08 g mL^-1). The ecologically relevant endpoint of feeding was measured by determining the amount of prey consumed (Artemia salina) after 30 and 60 min. The amount of microplastics ingested was also recorded at 30 min and 60 min. After which Hydra attenuata were transferred to clean media and observed after 3, 24, 48 & 96 hrs with changes in their morphology and reproduction (Hydranth numbers) recorded. The results of this study show that Hydra attenuata are capable of ingesting microplastics, with several individuals completely filling their gastric cavities. Significant reductions in feeding rates were observed after 30 min in 0.02 & 0.08 g mL^-1 and after 60 min in 0.04 & 0.08 g mL^-1 exposures. Exposure to the microplastics caused significant changes to the morphology of Hydra attenuata, however these changes were nonlethal. This study demonstrates that freshwater Hydra attenuata is capable of ingesting microplastics and that microplastic can significantly impact the feeding of freshwater organisms.