Seasonal succession of the travertine‐forming desmid Oocardium stratum

Abstract

The calcifying Conjugatophyte Oocardium stratum occurs exclusively in spring-associated limestones (SAL) with active meteogene limestone deposition. The macroscopic colonies of Oocardium stratum form hemispherical, pinhead-like structures with a diameter of 0.5-2.0 mm. As its autecology is still poorly understood, we focused on the seasonal development of Oocardium stratum and linked environmental factors to its abundance. The study was conducted in a rivulet in Lunz/See (Austria) for 16 months on a weekly (growing season) to monthly (winter season) basis. Oocardium colonies were found throughout the whole year, with maximum abundance during the mid-summer months July and August. Repeated macro-mapping of three SAL sites measuring 750 cm(2) each showed a maximum Oocardium cover of around 30% in August; two smaller peaks developed in early summer and late autumn with ~10% cover. Diatom mats dominated by Cymbella excisiformis occurred in spring, autumn and winter, with more than 75% cover. The seasonal change between Oocardium and diatoms in limestone-precipitating springs causes a typical sequence pattern of limestone layers. Redundancy analysis revealed water temperature and bicarbonate content as the main structuring factors; these control the occurrence and growth of Oocardium, reflecting season as a background variable. Optimum growth conditions for Oocardium were an alkalinity around 4.7 meq · L(-1) and a water temperature around 13°C. Site openness, nitrate and dissolved carbon dioxide were inversely related to Oocardium biomass, the opposite for diatoms. Other environmental factors such as total ions or soluble reactive phosphorus had no significant influence on Oocardium stratum abundance.

A freshwater analog for the production of Epiphyton‐like microfossils

“…Second, Epiphyton microfossils are often found filling voids and/or growing down (Adachi et al., ; James, ; Reid & Pfeil, ). The Oocardium method of copious EPS secretion not only allows Oocardium cells to remain attached but also allows Oocardium colonies to persist and thrive in high‐energy hydrodynamic conditions (Linhart & Schagerl, ; Lugli et al., ; Sanders & Rott, ). It is possible that this unique method of attachment and preference for rapid carbonate precipitation observed in modern Oocardium colonies (~4–10 mm per year; Sanders & Rott, ; Linhart & Schagerl, ) can be used to explain why Epiphyton is found closely associated with archaeocyath‐microbial reefs, which are known to occur in turbulent hydrodynamic conditions (James & Gravestock, ; Rowland & Shapiro, ).…”

“…The Oocardium method of copious EPS secretion not only allows Oocardium cells to remain attached but also allows Oocardium colonies to persist and thrive in high‐energy hydrodynamic conditions (Linhart & Schagerl, ; Lugli et al., ; Sanders & Rott, ). It is possible that this unique method of attachment and preference for rapid carbonate precipitation observed in modern Oocardium colonies (~4–10 mm per year; Sanders & Rott, ; Linhart & Schagerl, ) can be used to explain why Epiphyton is found closely associated with archaeocyath‐microbial reefs, which are known to occur in turbulent hydrodynamic conditions (James & Gravestock, ; Rowland & Shapiro, ). A similar method of EPS attachment may have assisted Epiphyton colonies to not only remain attached under turbulent conditions but also as a mechanism to survive the high rates of calcium carbonate precipitation typical of reef settings.…”

“…Second, Epiphyton microfossils are often found filling voids and/ or growing down (Adachi et al, 2015;James, 1981;Reid & Pfeil, 1983). The Oocardium method of copious EPS secretion not only allows Oocardium cells to remain attached but also allows Oocardium colonies to persist and thrive in high-energy hydrodynamic conditions (Linhart & Schagerl, 2015;Lugli et al, 2017;Sanders & Rott, 2009). It is possible that this unique method of attachment and preference for rapid carbonate precipitation observed in modern…”

“…Oocardium colonies (~4-10 mm per year; Sanders & Rott, 2009;Linhart & Schagerl, 2015) can be used to explain why Epiphyton is found closely associated with archaeocyath-microbial reefs, which are known to occur in turbulent hydrodynamic conditions (James & Gravestock, 1990;Rowland & Shapiro, 2002). A similar method of EPS attachment may have assisted Epiphyton colonies to not only remain attached under turbulent conditions but also as a mechanism to survive the high rates of calcium carbonate precipitation typical of reef settings.…”

Exploring the niche of a highly effective biocalcifier: calcification of the eukaryotic microalga Oocardium stratum Nägeli 1849 in a spring stream of the Eastern Alps

“…Only over the past decade or so, an increasing number of springs became identified in which calcification is largely mediated by the unicellular eukaryotic alga Oocardium stratum (Sanders and Rott 2009;Rott et al 2010Rott et al , 2012Sanders et al 2011;Ibarra et al 2014;Linhart and Schagerl 2015;Cantonati et al 2016;Trobej et al 2017;Grüninger and Günzl 2018). This taxon belongs to the coccoid zygnemataleans (or desmids), a group of freshwater algae that is placed into the green algae sensu lato together with other ancestral lineages of land plants, such as the Charophyta (Streptophyta, e.g., Gontcharov et al 2003).…”