Mixotrophic nanoflagellates in coastal sediments in the western Baltic Sea

Abstract

Benthic mixotrophic nanoflagellates (MNF) were studied in coastal sediments in Kiel Fjord, western Baltic Sea. Three types of surface sediment of different grain size were investigated, each along a vertical gradient within the first centimeter depth. A tracer experiment using fluorescently labeled bacteria (FLB) was conducted to identify MNF and quantify their contribution to total bacterivory in different sediment types and depths. MNF abundances and their phagotrophic activity did not vary significantly with sediment depth and grain size. Overall, mixotrophs contributed less to total nanoflagellates in sediments from Kiel Fjord (max. 2 %) than those recorded from comparable pelagic systems, contributing a higher percentage to total phytoflagellates than to the total bacterivores (5 to 10 vs. 2 to 5%, respectively). Potential reasons for these findings could be extensive niche segregation for bacterial grazers, osmotrophic feeding strategies in sediments due to high bacterial abundances and/or rarely limiting nutrient conditions. © Inter-Research 2006.