Page - 155 - in Freshwater Microplastics - Emerging Environmental Contaminants?

sediments, fluid feeders feed on other biotas fluids, and suction feeders ingest the prey together with the surrounding water. The utilized morphological structures determine further classifications. For example, filter feeders (e.g., daphnids) use specialized filtering structures to strain suspended particles, and raptorial feeders (e.g., copepods) actively capture and process suspended particles by modified appendages.Further typicallyusedclassificationsarecollectors(e.g.,chironomids), shredders (e.g., amphipods), scrapers (e.g., gastropods), and predators (e.g., odo- nates) [7]. Another way to categorize species is based on their diet. For instance, bacterivores feedonbacteria,herbivores feedonplants, carnivores feedonanimals (e.g., zooplanktivores, insectivores), and detritivores feed on decomposingmate- rials. These groupings imply clear boundaries, although some species feed on multiple food sources (e.g., generalist, omnivorous) or have the ability to switch between food sources (opportunistic feeders). Primaryproducers likeunicellularalgaeorbacteriaaswellasparticulateorganic matter (POM) provide nutrients for a broad range of pelagic and benthic species. Thus, smallMPsare ina similar size range to thenatural foodof theseconsumers. To understand the capacities of different species to feed on specific size classes, limnologistshave frequentlyusedpolymerbeadsas tracers [8–10].Although these studiesprimarily focusonpelagiczooplanktoncommunities, they illustrate that the intake of food and MPs depend on complex interactions between biotic (e.g., feeding type, physiological state, competition, food size, and availability) and abiotic factors (e.g., temperature). Accordingly, they provide a useful starting point to discussMP ingestion and effects. 2.1 TheRole ofFeedingTypes 2.1.1 Invertebrates Suspension andfilter feeders like protozoans, rotifers, cladocerans, andmussels are assumed to be especially prone toMP ingestion because they commonly feed on suspended particulatematter (SPM) and ingest a variety of seston components. The ingestion of MPs by these feeding types has been shown in numerous studies (Table 1). For instance, bacterivorous and herbivorous ciliates (e.g.,Halteria sp.), flagellates (e.g., Vorticella sp.), rotifers (e.g., Anuraeopsis fissa), and cladocerans (Daphnia sp.) can feed readilyonplastic beads [9, 10].Whiledata onMP ingestion bypelagicfilter-feedingzooplankton is relatively abundant, oneprominent groupof filterfeeders, thebivalves, isunderrepresented.Bivalvesareknowntofeedeffectively on SPM, includingMP, which is ingested bymarinemussels (e.g.,Mytilus edulis, [24]) and freshwater clams (Sphaerium corneum, 1–10 μmpolystyrene (PS) beads; Anodontacygnea,5–90μmpolystyrene(PS)beadsandfragments;unpublisheddata). In addition toorganisms specialized in feedingonSPM,avariety of organisms forage for particles in sediments. AlthoughMP exposure may be as relevant for deposit feeders (feeding on fine particulate matter and associated biota in sedi- ments) as for filter feeders, only a few studies have investigated the ingestion of MPs for this mode of feeding. The blackworm Lumbriculus variegatus and the Interactions ofMicroplasticswithFreshwaterBiota 155