Trophic coupling of the microbial and the classical food web in Lake Baikal, Siberia

Abstract

Pelagic copepods often couple the classical and microbial food webs by feeding on microzooplankton (e.g. ciliates) in oligotrophic aquatic systems, and this consumption can trigger trophic cascades within the microbial food web. Consumption of mixotrophic microzooplankton, which are both autotrophic and heterotrophic within the same individual, is of particular interest because of its influence on carbon transfer efficiency within aquatic food webs. In Lake Baikal, Siberia, it is unknown how carbon from a well‐developed microbial food web present during summer stratification moves into higher trophic levels within the classical food web. We conducted in situ experiments in August 2015 to test the hypotheses that: (a) the lake's dominant endemic copepod (Epischura baikalensis), previously assumed to be an herbivore feeding on diatoms, connects the microbial and classical food webs by ingesting ciliates; and (b) this feeding initiates top‐down effects within the microbial food web. Our results supported these hypotheses. E. baikalensis individuals consumed on average 101–161 ciliates per day, obtaining 96%–98% of their ingested carbon from ciliates and the remainder from small diatoms. Clearly, E. baikalensis is omnivorous, and it is probably channelling more primary production from both the microbial food web and the classical food web of Lake Baikal to higher trophic levels than any other pelagic consumer. Most ciliates consumed were a mixotrophic oligotrich and such taxa are often abundant in summer in other oligotrophic lakes. Consumption of these mixotrophs is likely to boost substantially the transfer efficiency of biomass to higher trophic levels with potential implications for fish production, but this has seldom been investigated in oligotrophic lakes. Feeding of E. baikalensis initiated a three‐link predatory cascade which reduced the abundance of ciliates and elevated growth rates of heterotrophic nanoflagellates but did not affect abundance or growth rates of autotrophic picoplankton. This demonstration of a potential trophic cascade in Lake Baikal indicates that investigations at larger spatial–temporal scales are needed to identify the conditions promoting or precluding trophic cascades in this lake.

Ice-on and ice-off dynamics of ciliates and metazooplankton in the Łuczański Canal (Poland)

“…It is well documented from both laboratory and field experiments that ciliates are a valuable, but still not appreciated, food resource for metazooplankton, including rotifers (Arndt 1993;Weisse and Frahm 2001;Ventelä et al 2002;Bielańska-Grajner et al 2011), cladocerans and copepods (e.g. Carrick et al 1991;Sanders and Wickham 1993;Wiackowski et al 1994;Zöllner et al 2003;Wiąckowski and Kocerba-Soroka 2017;Moore et al 2019), and fish larvae (Zingel et al 2019), due to the considerable contents of polyunsaturated fatty acids (PUFA) and sterols (Sommer et al 2012;Makhutova et al 2013) as well as nitrogen and phosphorus (Martin-Creuzburg et al 2005). Thus, small ciliates may enrich the diet of consumers even when they constitute only a minor part of the carbon diet (Sommer et al 2012).…”

Hot and sick: impacts of warming and oomycete parasite infection on endemic dominant zooplankter of Lake Baikal

“…Epischura baikalensis: As the dominant pelagic consumer in Lake Baikal, E. baikalensis 151 represents a key energy link in the food web of the lake (Yoshii et al 1999; Moore et al 2019). 152 E. baikalensis completes two generations per year in Lake Baikal: a winter and a summer 153 generation (Afanasyeva 1977).…”

Pretreatment Method for DNA Barcoding to Analyze Gut Contents of Rotifers

“…Primers were selected for specific detection of each potential prey community for rotifers. Phytoplankton and the components of the microbial food web (bacteria and protozoa) were considered as potential food sources for rotifers [6]. At this time, since we could not find a suitable primer to detect only heterotrophic nanoflagellates (HNF) specifically, we applied a universal primer for eukaryotes to HNF [38,39].…”

“…In particular, rotifers are critical components linking microorganisms with larger predatory organisms such as crustaceans and fish within the grazing food chain: bacteria, heterotrophic nano-flagellates, rotifers/copepods/cladocerans, larval fish, mature fish [2,3]. Consequently, they function as a channel for the flux of organic matter within diverse organism assemblages organized in an intermediate position between the two different food webs, and transfer nutrients and energy from the microbial loop to higher trophic levels [4][5][6]. In addition, as the problem of eutrophication increases in aquatic ecosystems, the abundance of macrozooplankton Appl.…”