Periphyton communities

Periphyton communities of microalgae on the submerged stems of Totora 

Prepared by William Lanza Aguilar (IE/UMSA)

We sampled the periphyton microalgal community only at stations with the presence of Totora (Schoenoplectus californicus ssp. tatora), an endemic emergent aquatic macrophyte, as the periphyton was collected by shallow scraping of its stems. Thus, it was not sampled at deep stations such as the Buoy (BH, 10 m) or Chua trench (LC, 40 m). We identified microalgae to genus level with density estimation (org/mL). We represented the results as bar graphs and relative abundance maps (%). We performed linear regression analysis to identify relationships between genera and nutrients. 

We recorded 57 genera distributed in 5 groups (phyla): Bacillariophyta (= Diatoms) with 20 genera; Chlorophyta with 15 genera; Cyanobacteria with 12 genera; Charophyta with 8 genera; Euglenozoa (= Euglenophyta) with 3 genera; and Miozoa with only 1 genus. The density of microalgae in the periphyton generally showed a dominance of the Bacillariophyta or "Diatoms" group; on average it was 52 %. In fact, diatoms have been reported as the dominant group in the periphyton associated with Totora, in studies conducted at TDPS (Lanza et al. 2017, Flores et al. 2019). 

The density (org/cm2) and composition of periphyton at the phylum level varied by study area and season. The densities per group or phyla (note: 'phyla' is the plural of 'phylum') of microalgae was highly variable. We found the highest densities (from 2,547 to 139,093 org/cm2) at the Cohana Bay stations (EC5 to EC10). Densities were also high at the Inca bridge of the Katari System (16,502 org/cm2, in SK10), Cumana (19,145 org/cm2 in NE4), Cojata Island (35,893 org/cm2), and Chojasivi (103,643 org/cm2 in CE17). The stations with the highest density presented a considerable predominance of green algae (Chlorophyta + Charophyta), particularly filamentous algae such as Oedogonium, Stigeoclonium and Spirogyra; as well as Cyanobacteria, with a greater occurrence of filamentous genera Oscillatoria, Geitlerinema, and Lyngbia. 

We performed a linear regression analysis to identify relationships between genera and groups with physicochemical variables. A significant positive relationship was identified between the sum of abundances of the taxonomic groups Chlorophyta + Cyanophyta (%) with phosphate concentration (Fig. 1 left). This indicates that the increase in abundance of these two groups would be a good indicator of the level of eutrophication. Our results are in agreement with some studies conducted in other regions, where a higher dominance of filamentous forms (Chlorophyta and/or Cyanobacteria) was recorded under eutrophic conditions (Cattaneo 1987, McCormick et al. 2001, DeNicola et al. 2006, Lu et al. 2016). Similarly, the genus Oedogonium (Chlorophyta) was positively related to increased phosphate. Also in their study, Schneider & Lindstrøm (2011) identified a similar relationship, suggesting that this genus is a good indicator of eutrophic conditions. Therefore, the abundance of the genus Oedogonium is a potential bioindicator of eutrophication for Lago Menor.

We developed distribution maps of relative (average) abundance (Fig. 2) for the Cyanobacteria, Chlorophyta and the genus Oedogonium. We observed a greater dominance of these groups and Oedogonium at stations near Cojata Island, Cumana Bay, Cohana Bay and Taraco Peninsula, suggesting that they present eutrophication conditions.