Stephanodiscus hantzschii fo. tenuis

Stephanodiscus hantzschii fo. tenuis was reported from nearshore and high energy zones of lakes Erie and Ontario (Reavie and Kireta 2015). It is considered characteristic of eutrophic lakes, particularly in higher total phosphorus concentrations (Reavie and Kireta 2015), and under silica limitation (Stoermer et al. 1979). This diatom secretes long chitin fibrils from the fultoportulae. The chitin fibrils help this diatom remain buoyant in the plankton. These fibrils are clearly observable in collections of living cells.

Blooms of S. hantzschii fo. tenuis regularly occur in Pike View Reservoir, a small urban reservoir in the city limits of Colorado Springs, CO. The water treatment plant operators regularly observe this diatom, and in large numbers, the cells clog filters. Often, cell numbers increase in late fall, but the largest blooms gain momentum in February and last until mid-May. In colder months, the blooms occur under ice-cover.

Pike View Reservoir has a maximum depth of about 3 meters. The date this sample (INSTAAR 17287) was collected there were approximately 60,000 cells/mL, temperature was 8 °C, pH 9.6, dissolved oxygen 15.2 mg/L, and conductivity 1130 umhos/cm (high probably due to influx of road salt). Two weeks previous, silica concentration was 13.8 mg/L. Blooms of S. hantzschii fo. tenuis significantly raise the pH of the reservoir.