Uptake of sub-micrometre- and micrometre-sized detrital particles by bacterivorous and omnivorous ciliates

Abstract

We used a new model type of detritus to observe and quantify the uptake of detrital particles by bacterivorous and omnivorous ciliates. It consisted of freshly prepared, fluorescently labeled dead organic particles. To represent autochthonous dead organic matter we chose the diatom Cyclotella meneghiniana, the green algae Monoraphidium minutum and Scenedesmus acutus, the copepod Cyclops abyssorum praealpinus and leaves of the macrophyte Elodea canadensis. Leaves of the copper beech Fagus sylvatica and grass stalks of Poa annua were considered as allochthonous detritus. The different types of organic matter were stained with the fluorescent dye DTAF and artificially disrupted to produce 7 different kinds of fluorescently labeled detritus (FLD) with a size spectrum of 0.2 to 20 μm (depending on the organic material we used). The uptake of 6 different kinds of FLD by the ciliates Dexiostoma campylum and Paramecium caudatum was demonstrated. Furthermore, a size dependent uptake of FLD was observed for the ciliate D. campylum and ciliates of the Stylonychia mytilus complex. Our study suggests that fine particulate detritus can be an additional food source besides bacteria or other picoplankton in the pelagic zone of lakes. This may increase the complexity of microbial food webs as well as the decomposition rate of particulate detritus.