Diatom communities on an artificial substratum at two contrasting sites at South Bay, Livingston Island

We used an artificial substratum (plexiglass tiles) to compare diatom communities at three different depths at two sites differing in their hydrological conditions and glacier melt-water influence. Samples at 1 m depth were taken during early summer in 2018, whereas samples at 3 m and 6.5 m were obtained in late summer 2020. The tiles were submerged for a period of up to 45 days in 2018, and up to 34 days in 2020. Water temperature, salinity, conductivity, oxygen saturation and concentrations, and Secchi depth were measured multiple times at both sites. During late summer of 2020 Photosynthetically Active Radiation (PAR) was also measured at depths of 3, 6.5 and 10 m at both sites. A total of 50 taxa constituted the diatom communities. Colonization and community development followed the same scheme at both sites and at all depths, with an early establishment of the dominant taxa, and a decline in species richness, diversity and evenness indices over the time towards relatively stable low values. Based on the results of PERMANOVA, ANOSIM and SIMPER analyses, diatom communities were site-specific, with 49% dissimilarity between the sites. Mechanical disturbances, such as wave action and ice scouring, as well as depth (and light availability) seemed to be the main factors driving the differences. The motile Navicula aff. perminuta dominated under mechanical disturbances at various light conditions, Navicula glaciei preferred calm shallow waters, and erect diatom growth forms were present in higher numbers in deeper waters with deteriorated light conditions.