Effects of temperature increase on the grazing of planktonic bacteria by biofilm-dwelling consumers

Abstract

ABSTRACT: Biofilms, the complex microbial communities associated with surfaces, can play animportant role in the flux of matter in running waters. In addition to bacteria and algae, heterotrophicprotists and small metazoans can also occur in high abundances in biofilms. By grazing on planktonicprey, biofilm-dwelling grazers can act as a trophic link between planktonic and benthic food webs,parallel to filter-feeding benthic macroinvertebrates. Here we introduce a flow cell method for thequantification of grazing rates of semi-natural biofilms on suspended bacteria, parallel to microscopicbiofilm community analysis. This technique was used to measure the temperature response of thegrazing rates of complex biofilm communities (established in a bypass system to the River Rhine, Ger-many) on planktonic bacteria. Results showed that 14 d old biofilms (dominated by ciliates) clearplanktonic bacteria at rates between 29 (in winter) and 99 l m –2 biofilm d –1 (in summer) at ambienttemperature. These rates increased with test temperature, even at temperatures (>30°C) at which thegrazing rates of filter-feeding macrofauna in moderate climates are negatively influenced. The accli-mation temperatures under which the biofilm developed can have a significant effect on communityclearance rates, largely due to a temperature effect on the abundance and structure of the grazercommunity, whereas no indication of an acclimation effect on individual grazing rates could befound. In the function of bentho-pelagic couplers, biofilm-dwelling consumer communities can reactto temperature changes substantially faster than macrofaunal filter feeders.KEY WORDS: Biofilms · Ciliates · Protists · Bentho-pelagic coupling · Ingestion rates · Picoplankton ·Running waters · Periphyton