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Ecological preferences of freshwater Ulva flexuosa (Ulvales; Ulvophyceae) : development of macroalgal mats in a Tulce fishpond (Wielkopolska Region, Poland)

Rybak A. S.

Oceanological and Hydrobiological Studies

2016

Vol. 45, No. 1

100--111

Research on the diversity of thalli and mats built by freshwater Ulva flexuosa, as well as the impact of abiotic factors on the development and distribution of Ulva mats, was conducted from May to August 2013. The study describes the dynamics of “green tides” formation by U. flexuosa. The study assessed abiotic factors that may influence the colonization and the growth of Ulva populations in freshwater systems. The results are of major importance to the trade and industry sectors. In total, eleven environmental parameters were included in the analysis. The most important environmental parameters characterizing the Ulva sites are sodium chloride levels and conductivity. High values of pH inhibited the development of Ulva, leading to a lower percentage of mature thalli in the mats. The water depth was positively correlated with an increase in the density of thalli in the mats and the average thallus length. Significant differences were identified between the concentrations of nitrates under and outside the Ulva mats. Concentrations of nitrate under the Ulva thalli were always lower.

Differentiation of inland Ulva flexuosa Wulfen (Ulvaceae, Chlorophyta) from Western Poland

Rybak A. S., Czerwoniec A.

Oceanological and Hydrobiological Studies

2015

Vol. 44, No. 3

393--409

The macroalgae representing the cosmopolitan Ulva flexuosa Wulfen species have been found in inland water ecosystems of Europe since the mid-1800s. The presence of the Ulva genus in waters of inland salt marshes was explained by high salinity of water in such systems. However, Ulva flexuosa thalli were found in lakes and rivers having no supply from strongly mineralized sources, either of natural or anthropogenic origin. The study focused only on populations of Ulva flexuosa subsp. pilifera (Kűtz.) M.J. Wynne and Ulva flexuosa subsp. paradoxa (C. Agardh) M.J. Wynne occurring in inland ecosystems isolated from seawater. The differentiation of inland U. flexuosa subsp. pilifera and subspecies paradoxa was assessed by using classical morphological data and molecular techniques. We found that only two subspecies of Ulva flexuosa Wulfen occur in inland water ecosystems of Poland. On the basis of the analysis combining morphological features with the ITS region and rbcL gene sequences, a small degree of differentiation of the two inland taxa was demonstrated. These two subspecies have high differentiation of the habitat niches. U. flexuosa subsp. paradoxa settled in habitats featuring high salinity levels, and the second subspecies pilifera occurred only in fresh waters.