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

Abstract

Water residence time in the middle course of rivers is often too short to allow substantial phytoplankton development, and primary production is essentially provided by benthic phototrophic biofilms. However, cells occurring in the water column might derive from biofilm microalgae, and, reciprocally, sedimenting microalgae could represent a continuous source of colonizers for benthic biofilms. A comparative study of biofilm and pelagic microphytic communities (with special focus on diatoms) was carried out over 15 mo in the Garonne River, France. Diatoms dominated both biofilm and pelagic microphytic communities. Typically benthic diatoms were found in high abundance in the water column, and their biomass in the water was correlated with their biomass in the biofilm, indicating the benthic origin of these cells. Variations in river discharge and temperature drove the temporal distribution of benthic and pelagic communities: under high flow mixing (winter) communities showed the greatest similarity, and during low flow (summer) they differed the most. Even during low flow, typical benthic species were observed in the water column, indicating that benthic−pelagic exchanges were not exclusively due to high water flow. Moreover, during low flow periods, planktonic diatoms typically settled within biofilms, presumably because of higher water residence times, and/or upstream reservoir flushing.KEY WORDS: Periphyton · Distribution · Biofilm · Microphytobenthos · Phytoplankton · Algal ecology · Community structure · HPLC Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 69: [47][48][49][50][51][52][53][54][55][56][57] 2013 Benthic algae on the river bed are generally associated with heterotrophic microorganisms (bacteria, flagellates and ciliates) embedded in a mucous matrix composed of exopolymeric exudates (EPS) and trapped detritic and mineral particles, to form biofilms (Lock et al. 1984, Romaní et al. 2004. These biofilms are shaped by abiotic and biotic influences (e.g. light, flow, nutrients, grazing, allelopathy) that affect their structure and functions (e.g. Hillebrand 2002, Sabater et al. 2002, Lyautey et al. 2005a, Boulêtreau et al. 2006, Mathieu et al. 2007). The dynamics of epilithic biofilms include a growth phase, corresponding to an ecological succession of microbial colonizers onto the substratum (e.g. Korte & Blinn 1983, Lyautey et al. 2005a, and a detachment phase. 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. Conversely, drifting microalgae could represent a continuous source of...

Selective Feeding of Bdelloid Rotifers in River Biofilms

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Reservoirs override seasonal variability of phytoplankton communities in a regulated Mediterranean river

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