Chlorella‐bearing ciliates dominate in an oligotrophic North Patagonian lake (Lake Pirehueico, Chile): abundance, biomass and symbiotic photosynthesis

Abstract

1. Large mixotrophic ciliates (Stentor araucanus, S. amethystinus and Ophrydium naumanni) were a characteristic component of a temperate, oligotrophic lake in North Patagonia. During a 1‐year study, the abundance, biomass and primary production of these large Chlorella‐bearing ciliates were compared with those of the total plankton community. 2. Mixotrophic ciliates peaked in spring and from late summer to autumn, accounting for 1.6–43% (annual average: 16.3%) and 67–99% (annual average: 92%) of total ciliate abundance and biomass, respectively. Their contribution to total zooplankton biomass, including flagellates, rotifers, ciliates and crustaceans, was 14–76%, or 47% as an annual average. Endosymbiotic algae accounted for up to 25% of total autotrophic biomass (annual mean: 3.9%). 3. Maximum cell‐specific photosynthetic rates of S. araucanus and S. amethystinus at light saturation varied between 80 and 4400 pg C ciliate–1 h–1 with high values during autumn and winter, and low values during summer. The depth‐integrated rates of photosynthesis (0–40 m) of algal endosymbionts contributed 1–25% to total photosynthesis (annual mean: 6.5%). 4. A comparison of calculated ingestion rates with photosynthetic rates of Stentor indicates that photosynthate produced by endosymbionts generally exceeded heterotrophic food supply of Stentor during autumn and winter, but was much lower during summer, when food supply was high. 5. The mixotrophic ciliates represent an important ‘link’ between nanoplankton and higher trophic levels within the plankton community because of their high heterotrophic biomass and considerable contribution to total photosynthesis.

Acquired phototrophy in aquatic protists

“…and Ophrydium spp. with algal endosymbionts can dominate the annual ciliate biomass and make an important contribution to total photosynthetic biomass in some oligotrophic lakes (Beaver & Crisman 1989a, Bienert et al 1991, Woelfl & Geller 2002 (Table 1). Maristentor dinoferus is conspicuous on coral reefs in Guam (Lobban et al 2002).…”

Effect of UV‐B and different PAR intensities on the primary production of the mixotrophic planktonic ciliate Stentor araucanus

“…However, this situation may not apply to the UV-B-resistant mixotrophic heterotrich Stentor araucanus. This species was found in the upper levels of clear-water lakes (Modenutti et al 1998;Woelfl and Geller 2002) and is highly resistant to UVR: it survived after 72 h of exposure to solar and artificial UV-B (Modenutti et al 1998), doses lethal to other organisms such as Daphnia pulicaria (Zagarese et al 1994). S. araucanus is a planktonic endemic ciliate species described by Foissner and Woelfl (1994).…”

Inter-annual ciliate distribution variation within the late stratification oxycline in a monomictic lake, Lake Alchichica (Mexico)

“…However, much information was obtained from permanently stratifiedmeromictic lakes (Psenner and Schlott-Idl, 1985;Oikonomou et al, 2015Oikonomou et al, , 2015 that might be different comparing to common stratified lakes. Penetration of photosynthetically active radiation (PAR) through a density gradient such as a thermocline or halocline (in meromictic lakes) is very important for picocyanobacteria-following feeders (Modenutti et al, 2002;Callieri, 2007;Peštová et al, 2008;Bautista-Reyes and Macek, 2012) and for zoochlorella and kleptoplasts or kleptochloroplasts-possessing mixotrophs either aerobic (Berninger et al, 1986;Modenutti and Balseiro, 2002;Woelfl and Geller, 2002) or those related to anoxic boundaries (Guhl and Finlay, 1993;Finlay et al, 1996;Finlay and Esteban, 1998;Oikonomou et al, 2015). Also, in the absence of dissolved oxygen, ciliates could be a very active component of the microbial food web (Wagener et al, 1990;Esteban et al, 1993a, b;Massana and Pedrós-Alió, 1994;Finlay et al, 1996;Fenchel, 2012;Bautista-Reyes and Macek, 2012).…”