Page - 160 - in Freshwater Microplastics - Emerging Environmental Contaminants?

2.2.2 TasteDiscrimination Many species are able to identify particles with nutritional value. For example, some bacterivorous and herbivorous protozoan, rotifer, and copepod species do not ingest polymer particles in their preferred size ranges (Table 1). Studieswith fluorescently labeledbacteria have shown that someciliates (estuarineoligotrichs) and flagellates prefer bacteria over MPs, while other species (estuarine scuti- cociliates; e.g., Uronema narina) cannot discriminate between bacteria and MPs [32]. The essential role of “taste” in the feeding of zooplankton [14, 32, 33] was acknowledgedwhendiscussing thecomparabilityof feeding studieswith synthetic microspheres and labeledbacteria or algae [9, 10, 15]. In rotifers,Bosmina (clado- ceran), and copepods (calanoid and cyclopoid), DeMott [14] observed significant differences between feeding rates onflavored and non-flavored polymer particles. WhileBosmina and the rotiferFilinia terminalis preferred algal-flavored spheres over untreated ones, D. magna and Brachionus calyciflorus did not [14]. This degree of selectivity was even higher in feeding trials with copepods. Here, calanoid (e.g., Diaptomus siciloides) and cyclopoid (e.g., Cyclops bicuspidatus thomasi) species strongly avoideduntreatedpolymer spheres [14]. Despite the abundance of studies that illustrate pelagic zooplankton feeding on MPs, information about benthic invertebrates and vertebrates in general is scarce. Although drawing conclusions for unexamined species is highly speculative, knowledge on zooplankton can be used as a template to a certain extent. The examined species cover a broad spectrum in terms of their autecology (feeding types, selectivity, and food preferences). The same is true for the unexamined species,which inhabit similarnichesandhaveequallydiverseautecologies.There- fore, we hypothesize a similar pattern regarding species-specific size and taste discrimination: Some species will directly feed on available MPs in the size rangeof their food,whilemore selective feederswill avoidMP ingestion. 2.3 Conclusion Primary consumers featuring bacterivorous, herbivorous, detritivorous, and deposit-feedingspeciesarecommonlyspecialized in foragingonparticulatematter andhave thecapacity to ingestMPparticles.Thedirect ingestionofMPsmightbe the major route for primary (e.g., herbivores) and secondary consumers (e.g., zooplanktivores),while apexpredators are additionally prone to an indirect inges- tionofMPsviaprey (foodweb).The limited literature suggests thatgeneralist and nonselective filter feeders (e.g., daphnids) have higher feeding rates compared to raptorial (e.g., copepods) and deposit feeders. Although studies on benthic invertebrates are scarce, specieswith detritivorous and omnivorous feeding types (e.g., Annelida, Insecta, Decapoda) may have the potential for ingesting MPs. 160 C.Scherer et al.