Ingestion and egestion of microplastic fibers in the green sea urchin Strongylocentrotus droebachiensis: An experimental exposure

Abstract

Plastic is a major component of marine litter in the world’s oceans and therefore it is critical we develop a better understanding of the fate of plastic in the marine environment, and the potential impacts on biota. Microplastics are the most abundant size class (<5 mm) of plastic found in the marine environment and have the potential to interact with smaller marine organisms at lower trophic levels. Microplastic fibers are a predominant type of microplastics found in the ocean, and in field studies of microplastics in benthic species. The main pathway of microplastic exposure to organisms is ingestion, which can be influenced by polymer type and biofouling state. A wide range of organisms ingest microplastic fibers, however without a better understanding of species-specific ingestion, retention, and egestion it is difficult to predict the potential ecological consequences. The current study exposed urchins to microplastic fibers, and wool as a natural fiber control, between 1 to 5 mm in length at a concentration of 128 fibers mL-1 for 48 hours. Fibers were exposed in two states, non-biofouled and biofouled. Post exposure urchins were kept for a depuration period of 86 hours. Intestines and faecal pellets were analyzed to investigate the influence of biofouling and fiber length on uptake, retention, and egestion of microplastic fibers. All urchins had ingested and egested microplastic fibers, but no statistically significant difference was found in ingestion or egestion between non-biofouled and biofouled fibers. Fiber length was not affected by urchin digestion. Findings about fiber retention was hampered due to low survival of urchins during the depuration period. Improvements in captivity conditions for future studies may be able to build upon understanding of retention time of microplastic fibers. This study demonstrated urchins can egested microplastic fibers in faecal pellets. As urchin faecal pellets are an important food source, microplastic fibers in faecal pellets could be an exposure pathway for other benthic species. Retained fibers in urchin intestines will be available for trophic transfer, potentially increasing the harmful impact of microplastic fibers in the environment.