Ulva flexuosa(Ulvaceae, Chlorophyta) inhabiting inland aquatic ecosystems: molecular, morphological and ecological discrimination of subspecies

Abstract

Species of Ulva (Ulvaceae, Chlorophyta) are relatively common macroalgae in most coastal areas. In this paper, we examine Ulva in inland aquatic ecosystems to determine relationships between the chemical parameters of the water and the Ulva taxa present. Two groups of samples of freshwater Ulva were selected from: (i) habitats with high salinity levels, and (ii) habitats with fresh or slightly saline waters. We showed that these two groups of Ulva, which occupy distinct habitats, represent two separate taxa. The first group represents Ulva flexuosa subsp. pilifera (Kützing) M.J. Wynne, which is very common and regularly encountered in fresh waters, but is equally well represented in slightly saline waters. The second is U. flexuosa subsp. paradoxa (C. Agardh) M.J. Wynne, which is less common, preferring mainly salt-wedge saline waters. We did not find both Ulva flexuosa subspecies together at any of the research sites.There were significant morphological differences between the Ulva flexuosa subspecies. Ulva flexuosa subsp. pilifera had longer and wider thalli and wider cells than those of subsp. paradoxa. Ulva flexuosa subsp. paradoxa cells were longer and of greater circumference than those of subsp. pilifera. Analyses of the rRNA ITS region and partial rbcL gene sequences demonstrated minor sequence variation within the two subspecies. The results of this study provide detailed information on the characteristics of limnic Ulva habitats and indicate the niches where such populations are likely to occur.

Polyphasic approach to a characteristic Ulva population from a limno-rheocrenic, mineral (chloride, sodium, sulphate) spring in the Siwa Oasis (Western Desert of Egypt)

“…paradoxa population occurs in a high-mineral-concentration (van der Aa 2003), chloride sodium sulphate, low-nitrate (due to biological consumption? ), oligo-mesotrophic (Dodds et al 1998) spring habitat (Table 1), in partial agreement with previous reports of the taxon in other parts of the world (Rybak et al 2014). Cyanobacterial taxa identified in Ain Abu Sherouf, such as Oscillatoria limosa and Phormidium tergestinum, suggest a relatively "polluted" (nutrient-rich) status (Komárek & Anagnostidis 2005).…”

“…In their recent contribution, Rybak et al (2014) reported samples of subsp. paradoxa with a comparable (although in average still larger) width of 50-400 µm, suggesting that very narrow filiform thalli may be in fact relatively common in this taxon (see Table S1 for more details).…”

“…A classical and authentic monography on the order Ulvales by Bliding (1963) identified five subspecies [including the subspecies paradoxa (C. Agardh) M.J. Wynne] and one variety as belonging to this species complex. Nevertheless, these taxa still form a taxonomic puzzle (Rybak et al 2014) and they are in need for in-depth combined studies, especially in Africa that is barely touched in this respect. Recent contribution of Kraft et al (2010) on the true species diversity of the genus Ulva in Australian waters identified some interesting U. flexuosa specimens only based on the anatomical structure but they also strongly suggested that this material might represent a novel or cryptic taxon because of its inconsistency with GenBank molecular data.…”

“…paradoxa can inhabit both marine and inland waters. In inland waters it is considered an indicator of mineral spring water habitats (Bliding 1963;Mareš et al 2011), occasionally present also in heavily anthropogenically impacted ecosystems rich in nutrient and salt content, and can tolerate salinity values exceeding 50 PSU (Rybak et al 2014;Rybak 2015Rybak , 2018. This represents a difference with respect to the similar subspecies pilifera, which seems to be restricted to freshwater habitats, such as ponds and small streams, and occurs under lower nutrient and salt concentrations on information available in the GenBank database, was another goal.…”

Freshwater population of Ulva flexuosa (Ulvaceae, Chlorophyta) as a food source for great pond snail: Lymnaea stagnalis (Mollusca, Lymnaeidae)

“…The seasonal collections of Ulva thalli were made at one location in the stream, and the species were identified using the ITS2 rDNA region and rbcL gene sequences, which were previously described by Rybak et al (2014). All specimens belonged to one species of green algae, Ulva flexuosa.…”