Diatom sampling
Samples of benthic biofilms were collected in the shoreline of 22 ponds in June 2018. Epiphytic diatom samples were collected from submerged stems of Schoenoplectus lacustris following the methodology proposed by Blanco, Ector, & Bécares, (2004). A scheme of the diatom sampling procedure and the subsequent processes is provided onFigure 2. A total of 10-12 stems were cut 10 cm below the water surface. Stems were placed in a plastic bottle with 500 ml of distilled water and shaken for 2 minutes to dislodge attached diatoms following previous studies (Zimba and Hopson, 1997; Riato, Leira, Della Bella, & Oberholster, 2018; Borrego-Ramos, Olenici, & Blanco, 2019). The suspension was split in two samples. One of them was fixed with 4% v/v formaldehyde and used for morphological identification, and the other one fixed with 70% v/v ethanol and used for molecular identification. All samples were transferred to the laboratory in a cool box. Samples for molecular identification were kept at -20 °C until DNA extraction.