New records of diatoms for the algal flora of Ukraine from water bodies of Nyzhniosulsky National Nature Park

Here we present new records of diatoms for the algal flora of Ukraine from water bodies of Nyzhnosulsky National Nature Park. The following species are recorded for the first time in Ukraine: Achnanthidium eutrophilum, Caloneis biconstrictoides, Encyonema lacustre, Gomphonema angusticephalum, Karayevia kolbei, K. suchlandtii, Placoneis abiskoensis, P. paraelginensis, Stauroneis balatonis, and Tryblionella salinarum. Some of them are rare and noteworthy taxa. For Caloneis biconstrictoides, it is the third known record in the world; Placoneis abiskoensis is a rare Holarctic species. The reported records of the new, rare and interesting taxa in the investigated water bodies may indicate a high nature conservation significance of Nyzhniosulsky National Nature Park as an algal reserve. The taxonomic position, synonymy, morphological features, information about ecology, distribution and original photomicrographs are provided.


Introduction
Although diatoms in Ukraine have been studied for more than 150 years, considerable territories of Ukraine remain poorly investigated until now. This is the case especially for the Left-Bank Forest-Steppe of Ukraine where, according to the literature data, only 350 species of diatoms have been reported (Algae of Ukraine…, 2009). In particular, one of the interesting areas in this respect is Nyzhniosulsky National Nature Park (NSNNP), located in the lower reaches of the Sula River in Poltava and Cherkasy regions. According to the algofloristic zoning of Ukraine, this territory belongs to the Poltava Plain Algofloristic District (Palamar-Mordvintseva, Tsarenko, 2015). A complex of various types of water bodies with different hydrological and hydrochemical parameters are presented in NSNNP (Nyzhniosulsky…, 2018). However, until now, data on the algal flora of the park were limited and did not represent the actual diversity of the diatom flora of this territory (Kryvosheia, Kapustin, 2019).
During the study of diatoms of NSNNP we revealed 284 species (285 infraspecies taxa, incl. typical ones) (Kryvosheia, Kapustin, 2019), including a number of new and interesting species for the flora of Ukraine which are presented in this article.

Materials and methods
Periphyton, plankton and benthos samples (38) from various types of water bodies of Nyzhniosulsky National Nature Park (N49°36′28′′, E33°11′27′′) were collected during different seasons in 2016-2017. Samples were fixed by 4% formaldehyde for later storage in the National Herbarium of Ukraine (KW-A). For diatom research, the samples were treated according to a standard technique using concentrated 35% H 2 O 2 (Prygiel, Coste, 2000). The obtained frustules were mounted in Naphrax® (refractive index 1.74) (Fleming, Roy, 1943). In addition, this material was used for scanning electron microscopy (SEM). Permanent slides were studied using light microscopes MBI-6 with phase contrast (LOMO, Russia), Olympus BX-53 (Olympus, Japan) and a scanning electron microscope JEM-1230 (JEOL, Japan) at the Center for the Collective Use of Electron Microscopes NASU.
In the article we followed the system of Medlin and Kaczmarska (2004) accepted in the series Algae of Ukraine…(2009), with some updates (Kulikovskiy et al., 2016).

Results and discussion
Ten species are newly reported for Ukraine. Their taxonomic position, synonymy, morphological features, information about ecology, distribution and original photomicrographs are given below.  Ecology. This species seems to be a northern one, in oligotrophic to mesotrophic lakes (Cox, 2003).
Note. According to E. Cox (2003), valves of this species have a length of 36-46 μm, while we found specimens with longer valves.
Central area transversely rectangular, occupies more than ½ valve width. Striae radiate throughout the valve, slightly wider apart at the centre of the valve, and shorter in the central area, 12 in 10 μm.
Ecology. Recent and fossil freshwater (Cox, 2003), occurs in waters with high level of mineralization and low level of organic matter (Bey, Ector, 2013b).
Note. With respect to its valve shape, it resembles Caloneis silicula var. tumida Hust. differing from the latter mainly by the presence of macula on the central area. Caloneis schumanniana var. biconstricta (Grunow) Reichelt differs in the valve shape with distinctly triundulated valve margins and strongly protracted and cuneate apices.
Distribution. Widely distributed in Europe, North and South America, Asia, Australia and New Zealand (AlgaeBase..., 2019).
Stauroneis balatonis Pantocsek (Fig. 1, H Distribution. This species was recorded only in lakes Ohrid and Prespa (North Macedonia), where it occurs in sediments from various water depths; it has a broad distribution in Europe as a fossil (under the name S. smithii var. incisa Pantocsek) (Levkov et al., 2016). Keel strongly excentric, with the central nodule formed by two fibulae. Fibulae 9 in 10 μm. Transapical ribs distinct, 12 in 10 μm. Striae indistinct in LM.
Ecology. This species occurs in salt-water of sea coast, brackish-water of river mouth and also in continental waters with high content of electrolytes, α-mesosaprobe (Lange-Bertalot et al., 2011).
Remark. The valves shape of this species is similar to that of T. levidensis W.Smith and T. calida (Grunow) D.G.Mann. However, T. levidensis has a smaller number of support ribs (7-10 in 10 μm) and T. calida has pronounced rostrate apices (Lange-Bertalot et al., 2011).

Conclusions
Ten species of diatoms were recorded for the first time in Ukraine. It is very likely that some of them have been previously found but not distinguished from the similar species. For instance, Gomphonema angusticephalum and Achnanthidium eutrophilum were formerly lumped under Gomphonema acuminatum Ehrenb. (Reichardt, 1999;Kulikovskiy et al., 2015) and Achnanthidium minutissimum (Kütz.) Czarn. (Lange-Bertalot, Metzeltin, 1996), respectively, and only recently were recognized as separate species.
Other species (e.g. Encyonema lacustre, Placoneis paraelginensis, Karayevia kolbei, K. suchlandtii, Tryblionella salinarum) are widely distributed but they have not been previously recorded in Ukraine due to the lack of detailed investigations. It should be noted that the record of T. salinarum, a species that prefers brackish waters, in the Sula River indicates the high electrolyte content of its waters. This conclusion is confirmed by hydrochemical analysis (Aqualandscape..., 2014).
Moreover, we have recorded several rare diatom species, such as Placoneis abiskoensis and Caloneis biconstrictoides. Stauroneis balatonis has a few extant records from lakes Ochrid and Prespa in North Macedonia (Levkov et al., 2016) but it is widely distributed in Europe and Asia as a fossil, known under the name S. smithii var. incisa Pantocsek.
Generally, the presence of the new, rare and interesting taxa in the water bodies of Nyzhniosulsky NNP may indicate its high nature conservation significance as an algal reserve.