Page - 158 - in Freshwater Microplastics - Emerging Environmental Contaminants?

Besides thesegeneral trends, available studies illustrate that speciesof the same functional feeding type have species-specific and sometimes highly divergentMP feeding rates. For instance, the filter-feeding cladoceransDaphnia longispina and Ceriodaphniaquadrangula ingested230 103PI 1h 1and176 103PI 1h 1, respectively. In comparison, rotifers (e.g.,Hexarthramira, 38.1 103 P I 1 h 1) and ciliates (e.g.,Halteria sp., 46.8 P I 1 h 1) ingestMPs at amuch slower rate [10].Whiledifferences aremainly causedby the species’morphologyandauteco- logy, numerous other factors (e.g., appetite,MP type and concentration, quantifi- cation methods) may also contribute. Overall, the most commonly studied invertebrate species are zooplankton.However,westill knowlittle about the inter- actions ofMPswith other prominent invertebrate freshwater taxa, e.g., Annelida, Insecta,Decapoda, andMollusca. 2.1.2 Vertebrates When considering vertebrate species,MPuptake is documented in laboratory and field studies for several fish species (Table 1). In contrast, no information is avail- able for amphibians. Considering the diversity of vertebrates acting as predators, herbivores,detritivores,oromnivores,wecanassume thatmanyspecies, at least in principle, have the capacity to ingestMPs depending on their feeding strategies. However, predictingMP ingestion by vertebrates solely based on feeding types maybe too short sighted. For instance, groupingfishes into specificguilds/feeding groups is an imprecise and difficult task. Indeed, typical terms like detritivores, herbivores,andcarnivoresaswellasgeneralist, specialist,andopportunistareused, but thevariabilityoffeeding(e.g.,duringdevelopment)andthetrophicadaptability (ability to switch food sources) impede aprecise classification [25]. The ingestion ofprey throughsuction feeding isutilizedby themajorityof teleosts,whichallows this high flexibility to exploit a variety of food sources [26]. Thus, accidental (mistakeMPs for prey) and indirect ingestion ofMPs (via prey containingMPs) are probable. The documentedMPs in several fishes collected in the field (e.g., catfish, perch, drum,Table 1) support this assumption. 2.2 TheRole ofParticle Size, Shape, andTaste 2.2.1 Size andShape The importance of particle size in the acquisition of particulate food has been studied for pelagic protozoans, rotifers, and crustaceans (e.g., [26, 27]). For filter- feeding taxa, a distinct relation between morphology and particle size has been observed. Here, theminimum ingested particle size is mainly determined by the mesh size of the filtering apparatus. The maximum size is determined by the morphology ofmouthparts and, in the case of cladocerans, the openingwidth of the carapace. Additionally, Burns [8] and Fenchel [27] describe a correlation 158 C.Scherer et al.