Acidophilic phytoplankton in Argentina: the case study of Lake Caviahue (Patagonia)

Abstract

This article presents a review of the studies carried out over a 10-year period in Lake Caviahue, a natural acidic lake located in Patagonia. The main patterns of the phytoplankton populations are described. Five extremophiles phytoplanktonic species were studied in relation to the zooplankton and nutrients bioavailability under the environmental conditions registered in Lake Caviahue: very low pH (~3), high concentrations of iron (18.4 mg L-1) and sulphur (130 mg L-1). During the 10-years studies, the biomass (0.2 and 1.4 mg fw L-1) and the biodiversity were very low being Keratococcus rhaphidioides the dominant species (60 to 100% of the total biomass). Philodina sp. (Bdelloidea) was the only zooplankter responsible of the zooplankton biomass. From the lack of relationship between phytozooplankton biomass, as well as from the results obtained in the feeding experiments, we conclude that no control of algal abundance by the zooplankton occurs. The microalgae were nitrogen limited in the lake and according to the results from experiments with nutrient addition, the phytoplankton showed nitrogen limitation on growth rate and yield. The species have also the capacity to use mixotrophically alternative sources of organic and inorganic carbon and organic nitrogen. The importance of the uptake and the expression of CO2 concentrating mechanisms (CCMs) were demonstrated in Euglena and in the ellipsoidal form of Watanabea but not in the spherical form of Watanabea and in Palmellopsis. The two forms of Watanabea differed in their possession of a CCM.