Changes in the phytoplankton community structure in a monomictic temperate lake

Abstract

Changes in the phytoplankton community structure in a monomictic temperate lakeThis study focused on the phytoplanktonic community of lake Sanabria (NW Spain) during the mixing period. We integrated the classic phytoplankton counting method and the pigment analysis via high performance liquid chromatography, to obtain a global image of the community structure, which was very similar among the study zones and unaltered despite a temporal increasing of biomass during this period. The diatom Asterionella formosa Hassall (around 80 %), and consequently the fucoxanthin were the species and the secondary pigment more abundant, respectively. This dominance contrasted with the studies performed in 90´s, where the community structure was distributed among chlorophytes, cryptophytes, diatoms, dinoflagellates and cyanophytes, with no clear and persistent dominance of any of the main taxonomic groups and an occasional presence of Asterionella formosa. However, the classical variables, such as nutrients or chlorophyll a concentration, used for trophic definition have barely changed since the studies of 90's. It is possible that other parameters, such as the residence time or the effect of the increase in the temperature since 90´s could have influenced the phytoplankton community structural changes observed.

Taxonomic composition, community structure and molecular novelty of microeukaryotes in a temperate oligomesotrophic lake as revealed by metabarcoding

“…The altered values of chlorophyll a in the east basin may be related to higher anthropogenic impact due to the presence of three camping sites on this side of the lake. Chlorophyll a values measured in Sanabriás east basin in March 2017 (Llorente and Seoane 2020) are lower than the ones presented in our study, implying that the stressor was temporal and that water quality has been restored.…”

“…Since 2012, the Duero International Biological station has raised concerns that Sanabria Lake is undergoing a eutrophication process due to contamination from a deficient sewage depuration system (Guillen, 2015). However, studies based on pigment measurements and microscopy observation of the phytoplankton community do not support the eutrophication scenario and confirm the current oligotrophic state of the lake (Pahissa, Fernández-Enríquez, and De Hoyos 2015; Llorente and Seoane 2020).…”

“…No anoxic conditions have been observed in any layer of the water column during the thermal stratification (Vega et al 1992;de Hoyos 1996;Pahissa, Fernández-Enríquez, and De Hoyos 2015). Sanabria Lake is considered as oligotrophic to oligomesotrophic in view of its low levels of chlorophyll a, nutrient concentration, phytoplanktonic biovolume values and production rates (Planas 1991;Vega et al 1992;de Hoyos 1996;Pahissa, Fernández-Enríquez, and De Hoyos 2015;Llorente and Seoane 2020;De Hoyos and Comín 1999). The oligotrophic state of the lake is a result of its geology.…”

“…The prevalence of Rhizophydiales in the Sanabria Lake ecosystem was not surprising given that they are the most common planktonic chytrids in lacustrine ecosystems (Monchy et al 2011). A species of Rhizophydiales was probably the causative agent of a chytrid infection in Sanabria Lake in 2014 that diminished the population of the diatom Tabellaria fenestrata and controlled an algal bloom caused by eutrophication (Llorente and Seoane 2020). The relative abundance of Perkinsea, a group of parasitic alveolates, ranged from 13% to 18% of total parasite abundance across the different sampling sites.…”

“…In comparison to lakes of other trophic states, oligomesotrophic lakes harbour the richest and most diverse lentic organismal communities (Lefranc et al 2005). Sanabria Lake is the biggest natural glacial lake in the Iberian Peninsula (Vega et al 2005) and has already been the subject of many traditional limnological studies (Taboada 1913;Margalef 1955;Aldasoro et al, 1992;Vega et al, 1992;De Hoyos, 1996;De Hoyos et al, 1998;De Hoyos and Comín, 1999;Negro, De Hoyos, and Aldasoro 2003;Luque 2002;Jambrina-Enríquez et al 2014;Pahissa, Fernández-Enríquez, and De Hoyos 2015; Llorente and Seoane 2020) Negro et al, 2000;Luque & Julià, 2002;Rico et al, 2007;Jambrina-Enríquez et al, 2014;Pahissa et al, 2015;Llorente and Seoane 2020). However, no molecular data are currently available for this freshwater system.…”