Luticola frequentissima Levkov, Metzeltin & Pavlov – morphological and ecological characteristics of a population from Southern Poland

The genus Luticola differs from Navicula sensu stricto in nearly every aspect of valve morphology and cell organization. It is a large genus with around 200 different species (Levkov et al. 2013). Luticola mutica D.G. Mann in Round et al. (1990) is typus generis for the genus Luticola D.G. Mann. Cells are usually lanceolate, linear or elliptic, with differently developed ends. The central area is transversely rectangular with one single stigma on one site. In the external view, the stigma is rounded or elongated, whereas in the internal view, in most of the taxa, it is covered by a circular and lipped structure. Striae are composed of a few areolae. Diatoms from the genus Luticola occur most frequently in freshwater or slightly saline waters, in soils or subaerial habitats and in estuaries (Round et al. 1990; Hofmann et al. 2011; Bąk et al. 2012).

Over a dozen species from the Luticola genus (previously reported as Navicula) are known in Poland, the most common of which are: L. acidoclinata, Lange-Bert., L. cohnii (Hilse) D.G. Mann, L. goeppertiana (Bleisch) D.G. Mann, L. mutica (Kütz.) D.G. Mann, L. nivalis (Ehrenb.) D.G. Mann and L. ventricosa (Kütz.) D.G. Mann (Rakowska 2001; Siemińska, Wołowski 2003; Wojtal 2009; Bąk et al. 2012; Noga et al. 2014).

Luticola frequentissima Levkov, Metzeltin & Pavlov was described from the Vardar River in Macedonia and is widespread in freshwater, but can be confused with L. mutica (Kütz.) D.G. Mann. Both species can be distinguished by the shape of the central area, the striae morphology and in the case of L. mutica – by the presence of ornamented cribrum in areolae. In L. mutica, proximal endings are close to one another, while distal endings are hooked on to the valve mantle (Levkov et al. 2013). So far, the species has not been recorded in Poland.

This paper presents new sites as well as ecological and morphological (including SEM) characteristics of Luticola frequentissima Levkov, Metzeltin & Pavlov in south-eastern Poland.

The study was conducted in the catchment areas of two large rivers: the Wisłoka River, which flows through the Magura National Park and the Wołosaty River, which flows through the Bieszczady National Park (Fig. 1).

Figure 1

The Wisłoka, which is a right-bank tributary of the Vistula River, begins its course at an elevation of 664 m a.s.l. The length of the Wisłoka River is 164 km, and the catchment area is 4 110 km². The upper and middle parts of the Wisłoka catchment area are composed of Tertiary and Quaternary flysch strata, i.e. sandstone and siltstone, and rarely marl and conglomerates (Buszko & Kiryk 1995; Boratyn & Brud 1996). Rock layers of varying thickness are arranged alternately and they make up the so-called Carpathian flysch (Klimaszewski & Starkel 1972; Winnicki & Zemanek 2014). This area is characterized by low- and medium-height mountains (650-700 m a.s.l.), and is covered by forests and scrubs in 90%, mostly within the territory of the Magura National Park. The analyzed streams show large changes in the water level, which is typical for mountain rivers. During rainless periods, the stream flow is very small and in summer, the water temperature is high (Soja 2009). The study area is sparsely populated with a small amount of tourist traffic, while single small farms are located within the buffer zone of the park.

The Wołosaty stream (the upper section of which is called ‘Wołosatka’) is a right-bank tributary of the San River. The upper part of the Wołosaty catchment area is 8.32 km² and is located between the peaks of Tarnica, Halicz and Rozsypaniec (Siwek et al. 2009). The San is the richest river in terms of water and the largest river in the Carpathians (443.4 km length), the sources of which are located in Ukraine. Much of the San catchment area is covered by protected areas, including the Bieszczady National Park. The study area is part of the Western Bieszczady, also called the High Bieszczady (900-1300 m a.s.l.) and is composed of the Carpathian flysch. The area consists mainly of sparsely populated, natural and slightly transformed ecosystems. Some parts of this area are preserved in almost primeval conditions.

Samples were collected between 2013 and 2015 (September 2013, March and October 2014 and October 2015) in the catchment area of the Wołosaty within the Bieszczady National Park, and between 2013 and 2014 (April, July, August, October 2013 and April and October 2014) in the upper Wisłoka River within the Magura National Park (Fig. 1). Nine sampling sites were designated in the Wołosaty catchment area and 26 sampling sites in the catchment area of the Wisłoka. In total, the research covered 12 rivers and streams in the Magura National Park and 3 streams in the Bieszczady National Park (Table 1).

Table 1

Characteristics of the studied watercourses in Bieszczady and Magura National Park

Samples were collected and prepared according to methods used by Kawecka (1980) for river algae. Diatom samples were preserved in 4% solution of formaldehyde. A portion of each sample was cleaned with chromic mixture (a mixture of sulfuric acid and potassium dichromate), then washed in a centrifuge (at 2500 rpm). Diatoms were mounted in synthetic resin (Pleurax; refractive index 1.75).

Diatoms were identified and counted under a Carl Zeiss Axio Imager A2 microscope equipped with a 100× Plan Apochromatic objective with differential interference contrast (DIC) for oil immersion (NA 1.4). For scanning electron microscope (SEM) observations, samples were coated with 20 nm of gold using a Quorum Q 150OT ES Turbo-Pumped Sputter Coater and observed under Hitachi SU 8010 and Phenom Pro microscopes.

Species composition was determined in the collected samples by counting 400 specimens within randomly selected fields of view under a light microscope. Species with a content above 5% in a given diatom assemblage were defined as the most abundant.

Luticola frequentissima Levkov, Metzeltin & Pavlov was found only at two watercourses (Wołosaty and Terebowiec) within the Bieszczady National Park, in the Wisłoka River and in two small streams within the Magura National Park. The taxon was also found in the soil of the Wilsznia and Ryjak catchment areas, in the Magura National Park. Luticola frequentissima was recorded mostly in small and shallow streams, which dry up in summer.

Morphological description

Valves are lanceolate, rhombic-lanceolate to elliptic (especially small cells) and asymmetrical (Fig. 2a-ad). A detailed morphological description was made by Levkov et al. (2013), which is mostly consistent with our observations (Fig. 3). However, cells in the analyzed samples were much smaller, narrower and contained a larger number of striae. Valves of the studied material were 6.2-22.5 μm, with a breadth of 4.0-7.6 μm, and the number of striae ranged from 18 to 27 per 10 μm. Whereas Levkov et al. (2013) found that frustules were 12-27 μm in length, 6.5-9.0 μm in breadth and contained 20-24 striae per 10 μm (Table 2). Much smaller and narrower cells were also observed by Ector et al. (2015) in France (7.7-13.8 ´ 4.8-6.8 μm; 20-24 striae in 10 μm).

Figure 2

Figure 3

Table 2

Description of the sampling sites and valve dimensions of L. frequentissima

Sampling site	Bieszczady National Park		Magura National Park
	Wołosaty	Terebowiec	Ryjak’s tributary	Wisłoka	Wisłoka’s tributary	soil (Ryjak, Wilsznia catchments)
Date	03/2014	03/2014	07/2013	10/2013	04/201310/2014	04/201407/201410/2014
Insolation	high	low	low	high	low	high
Type of substrate	stones (large ones covered with moss)	stones	stones (near shore covered with mud)	stones	stones (large ones covered with moss)	soil overgrown with grass in ca. 50%
Temperature (°C)	5.6	6.1	13.4	10.2-11.7	8.1-11.8	-
pH	8.5	8.4	8.1	6.3-6.5	7.3-7.4	5.6-6.5
Conductivity (μS cm–1)	166	138	288	378-402	174-341	-
NO3- (mg l-1)	0.22	0.23	0.84	<0.01	1.91-5.76	-
SO42- (mg l-1)	16.37	13.74	18.78	20.39-26.53	18.20-21.26	-
L. frequentissima valve dimensions
Length (μm)	9.4	14.1	8-13.3	11.6-16.5	6.2-22.5	8.6-16.6
Breadth (μm)	5.0	6.6	5.5-6.2	4.0-6.0	4.4-7.6	5.1-6.4
Striae per 10 μm	22	21	23-27	22	18-21	22-27

According to Levkov et al. (2013), proximal raphe endings are long and hooked on the same site as proximal endings. In the present study, we found frustules with one proximal raphe end in the opposite direction to the proximal endings (Fig. 3j).