ALBERT

Description: Plastic pollution is an emerging global threat for marine wildlife. Many species of birds, reptiles and fishes are directly impaired by plastics as they can get entangled in ropes and drown or they can ingest plastic fragments which, in turn, may clog their stomachs and guts. Microplastics of less than 1 mm can be ingested by small invertebrates but their fate in the digestive organs and their effects on the animals are yet not well understood. We embedded fluorescent microplastics in artificial agarose-based food and offered the food to marine isopods, Idotea emarginata. The isopods did not distinguish between food with and food without microplastics. Upon ingestion, the microplastics were present in the stomach and in the gut but not in the tubules of the midgut gland which is the principal organ of enzyme-secretion and nutrient resorption. The feces contained the same concentration of micro-plastics as the food which indicates that no accumulation of microplastics happens during the gut passage. Long-term bioassays of six weeks showed no distinct effects of continu¬ous micro-plastic consumption on mortality, growth, and intermolt duration. I. emarginata are able to prevent intrusion of particles even smaller than 1 µm into the midgut gland which is facilitated by the complex structure of the stomach including a fine filter system. It separates the midgut gland tubules from the stomach and allows only the passage of fluids and chyme. Our results indicate that micro¬plastics, as administered in the experi¬ments, do not clog the digestive organs of isopods and do not have adverse effects on their life history parameters.

Description: Microplastics accumulate worldwide in marine habitats. Especially the surface waters of the oceans (including polar sea ice), the water column and seafloor sediments are contaminated by huge amounts of microplastics. Accordingly, most studies on the uptake of microplastics and their effects focus on species from these specific habitats. Marine benthic meso-herbivores, which live primarily associated with seaweeds on rocky shores, have been widely ignored in studies on microplastics presumably because this functional group of organisms is believed to be at low risk of encountering synthetic particles in their natural habitats. We tested whether seaweeds can collect microplastics from the water column and make them available for ingestion by marine meso-herbivores. In laboratory experiments pieces of the brown seaweed Fucus vesiculosus were incubated in microplastic suspensions and subsequently screened for adhering microplastics. We used different types of fluorescent microplastics including commercial beads, fragments and fibres. Microplastics readily adhered to the surface of the algal pieces. The particle density mostly correlated with the concentration of particles in the suspension. Tidal emergence and desiccation of contaminated algae did not enhance the adherence of the particles. In feeding assays algal pieces contaminated with microplastics were offered to the herbivorous periwinkle Littorina littorea. The gastropods did not prefer clean over contaminated algae indicating that they do not recognize solid non-food particles in the sub-millimeter size range as deleterious. In dissected periwinkles microplastics were found in the stomach and in the gut but not in the hepatopancreas, which is the principle digestive organ of gastropods. Substantial amounts of microplastics were released with fecal pellets indicating that the particles do not accumulate rapidly inside the intestines. Our results indicate that benthic seaweeds may function as a vector for the entry of microplastics into marine food webs at low trophic levels.