Contribution of biofilm-dwelling consumers to pelagic-benthic coupling in a large river

Abstract

Summary 1. Over the course of this 17‐month study, we assessed the potential loss of plankton (bacteria, algae, heterotrophic flagellates) to consumers (ciliates and rotifers) within mature biofilms established on natural substrata exposed to the main current of the River Rhine (Germany). Once a month, in flow cells in a bypass system to the River Rhine, we measured the clearance rates of the biofilm‐associated consumers on the different groups within the natural plankton. 2. Ciliates were the most dominant consumers, among which planktivorous groups, particularly peritrichs and (in spring and summer) heterotrichs dominated. Consumer biomass varied with season, with the highest density occurring directly after the appearance of the phytoplankton spring peak. 3. Clearance rates on plankton ranged from 96 to 565 L m−2 d−1 for bacteria and 66–749 L m−2 d−1 for algae, with a preference for algae in summer and for bacteria in winter. This pattern coincided with seasonal changes in the structures of the grazer communities. The consumers (both ciliates and rotifers with total standing stocks ranging between 19 and 572 mg C m−2) imported a substantial amount of organic matter (between 15 and 137 mg C m−2 d−1) into the biofilm. 4. These results highlight the potential importance of consumers in the biofilm as a trophic link between the plankton and the benthos, a function that has hitherto mostly been attributed to filter‐feeding bivalves. In contrast to bivalves, the biofilm‐dwelling consumers show a more dynamic response towards the plankton density and composition. Such dynamic components need to be considered when estimating total plankton consumption by the benthos.

Short-term effects of nutrient enrichment on river biofilm: N–NO3 − uptake rate and response of meiofauna

“…Nevertheless, our study shows that in rivers, where rotifers are important contributors to the biofilmdwelling meiofauna (Reiss & Schmid-Araya, 2008;Kathol et al, 2011;Majdi et al, 2012a), biofilm lotic meiofauna can potentially react rapidly to short-term nutrient enrichment (e.g. short-term nutrient pulses after rainfall-induced runoff from agricultural catchments).…”

“…Alternatively, since microalgal production was not measured, it can be envisaged that microalgal production might have been stimulated even though their biomass did not change. Considering that rotifers are effective grazers in river biofilms (Kathol et al, 2011;Mialet et al, 2013), the grazing of algae by increasing density of rotifer might on the one hand favour bacteria in the competition for N-NO 3 -and on the other hand keep the algal population in an active growth phase and hence stimulate N-NO 3 -uptake of the biofilms at high N-NO 3 -concentration. We can, hence, not exclude that stimulated microalgal growth also participated in the increased N-NO 3 -uptake in the enriched conditions.…”

Contribution of epilithic diatoms to benthic-pelagic coupling in a temperate river

“…Detachment of components of the biofilm can occur either through flow abrasion and/or through self-detachment processes (Biggs & Close 1989, Boulêtreau et al 2006. Also meio-and macrofauna drilling and grazing the biofilm influence its architecture and growth dynamics (Lawrence et al 2002, Gaudes et al 2006, Kathol et al 2011. In the middle course of fast-moving rivers, cells occurring in the water column are derived essentially from the detachment of phototrophic biofilms (Roeder 1977, Ameziane et al 2003.…”

Colonization dynamics of trophic-functional patterns of PFU protozoan communities in Dongchang Lake, northern China

“…The photoautotrophic group is responsible for the bulk of primary production (Cairns et al 1972;Xu et al 2010;Tan et al 2010;Zhang et al 2012). Heterotrophic protozoa can form complex communities with many different taxonomic and functional types in aquatic ecosystems (Parry 2004;Fru¨h et al 2011;Kathol et al 2011). Some bacterivorous protozoa can tolerate extreme environmental conditions and often play an important role in maintaining and improving water quality through their grazing activities (Norf et al 2009a(Norf et al , 2009bXu et al 2010Xu et al , 2012.…”

“…Protozoan grazers (e.g., groups B, A, and R) associated with surfaces utilize a variety of food particles, such as bacteria, algae, flagellates, small ciliates, and detritus particles Parry 2004;Scherwass et al 2005). General modes of food acquisition in protozoa are either the concentration of food particles from plankton origin by filter feeders (e.g., groups B and A) or the active search for food particles in the biofilm by gulper feeders, such as groups B, A, and R (Franco et al 1998;Parry 2004;Kathol et al 2011). Thus, the functional structure of the protozoan communities may represent significant changes during the initial colonization of biotopes due to the food supply (Kiørboe et al 2004;Norf et al 2009a;Wey et al 2009;Fru¨h et al 2011).…”