Marine benthic foraminifera and microplastics (Accumulation and effects following short- and long-term exposure)

Microplastics contaminate marine environments worldwide, but there is little knowledge of whether and how benthic foraminifera are affected. The aim of this project was to clarify whether microplastics accumulate in and affect benthic foraminifera. Sediment was collected at 163m water depth in the Oslofjord, Norway, on September 2018. Collected sediment was stored in a climate room 7C° at the Department of Biosciences, University of Oslo until further use. Treatments were prepared by adding one of three sized fluorescent polystyrene microspheres (0.5 μm; 1 μm and 6 μm) into containers with 10 mL of gently homogenized sediment. In the control treatment, no microplastic was added to the sediment. Two experiments were performed, exposing benthic foraminifera communities to microplastics for 6 hours and 4 weeks. Following both exposures, rose Bengal-stained foraminifera were identified, counted and the number of specimens with microplastics inside were counted. There was no significant change in community composition after exposure to microplastics (0.5 μm, 1 μm, 6 μm) for six hours or four weeks compared to control. Cluster and multidimensional scaling analyses showed around 85% similarity between samples from the two sampling times. Shannon diversity index of live foraminifera varied from 3.53 to 4.03. In total 17 species ingested microplastic in the six-hour experiment and 21 species ingested microplastic in the four-week experiment. In six-hour and four-week experiments, 8 and 13 species accumulated microplastic in at least three out of five replicates respectively. Most foraminifera did not differentiate between microplastic sizes, but two species differentially accumulated the three sizes of microplastics: Nonionella turgida accumulated 6 μm plastic particles more than 1 μm in the six-hour experiment and did not at all accumulate 0.5 μm plastic particles; Uvigerina peregrine accumulated 0.5 μm plastic particles more than 1 and 6 μm plastic particles in the four-week experiment. Most of the species accumulated more microplastic after 4 weeks compared to 6 hours. Thirteen foraminifera species accumulated more 0.5 μm microplastic in the four-week experiment than in the six-hour experiment; seven species accumulated more 1 μm microplastic in the four-week experiment than in the six-hour experiment; and ten species accumulated more 6 μm microplastic in the four-week experiment than in the six-hour experiment. Food preferences and test composition of foraminifera affected the accumulation of microplastics, whereas species with high tolerance to organic carbon and or their microhabitat preferences did not appear to influence the accumulation of microplastics. This study shows that there are differences in the accumulation of microplastics in foraminifera species. Accumulation of microplastics in foraminifera may be an entry of such particles into the marine benthic food webs.