Understanding species-microplastics interactions : a laboratory study on the effects of microplastics on the Azorean barnacle, Megabalanus azoricus

Abstract

Understanding the impact of microplastics on the marine environment, wildlife and humans is a complex issue. Effects of contaminated microplastics (polyvinylchloride (PVC), mean size 1.5 µm) on the Azorean barnacle (Megabalanus Azoricus) were investigated within a global research project (GAME), in which akin experiments were conducted simultaneously at seven different sites worldwide in order to obtain comparable data for a range of benthic invertebrates. During a six weeks laboratory experiment individuals of M. azoricus were exposed to different microplastic density levels and the effects of these treatments on barnacle survival, respiration, motility and survival under hypoxia stress were measured. The results do not allow clear statements on a negative effect of microplastics on barnacles. Cirral activity decreased under medium plastic densities, with barnacles showing no respiratory pumping and beating, but at higher densities the behavior of the barnacles was normal. A similar pattern was observed for the respiration rates in the medium plastic density treatment group,although no statistical difference emerged between this and all other groups. At high plastic densities barnacles may have protected themselves from exposure, while barnacles at lower densities did not manage to do this, maybe because the reflex of feeding was still intact at medium particle densities. Although this experiment did not give clear answers, a comparison with all other studied species showed that under similar conditions some were clearly affected, indicating that some species might be more susceptible to microplastic exposure.An additional investigation of sediment samples from a beach (Praia Formosa) in Southern Madeira should contribute to the understanding of actual microplastics abundance of the surrounding habitat of Megabalanus azoricus. The results suggest a rather low concentration with a mean microplastic abundance of 4 particles per kilogram sediment. This study illustrates how marine science deals with uncertainty and complexity. While some microplastic-species interactions produce inconclusive results, other studies deliver first evidence of the negative influence of microplastics. This study helps to understand specieslevel impacts of microplastic pollution for range of marine organism from the base of themarine food web. While trying to understand its effects on complex biological systems, it should be highlighted that microplastic pollution is irreversible, meaning there is no method suitable for removingit. There is abundant evidence of the presence of this contaminant in the ocean and the level of pollution is expected to grow. Thus, the precautionary approach is urged to be applied and research supporting mitigation of plastic pollution and decision-makers should be prioritized.