1. bookVolume 50 (2021): Issue 1 (March 2021)
Journal Details
License
Format
Journal
eISSN
1897-3191
First Published
23 Feb 2007
Publication timeframe
4 times per year
Languages
English
Open Access

A review of research on the Lemanea genus in Serbia

Published Online: 21 Mar 2021
Volume & Issue: Volume 50 (2021) - Issue 1 (March 2021)
Page range: 47 - 59
Received: 18 May 2020
Accepted: 13 Aug 2020
Journal Details
License
Format
Journal
eISSN
1897-3191
First Published
23 Feb 2007
Publication timeframe
4 times per year
Languages
English
Introduction

Identification of Lemanea species based on morphological features is very difficult due to multiple morphological variations, but also due to the fact that there are many synonyms in the literature (Kumano 2002; Eloranta et al. 2011). According to the available literature (Vis & Sheath 1992; Kumano 2002; Eloranta et al. 2011), differences between Lemanea species are based on diacritic features, mainly the length and width of the thallus, the way the sterile basal part transitions into the fertile part, branching, the arrangement of spermatangial papillae, the presence of the Chantransia stage, the length and diameter of Chantransia cells.

According to AlgaeBase (Guiry & Guiry 2020), 18 species of the genus Lemanea were flagged as taxonomically accepted based on morphological and reproductive features and molecular analysis. Eight of them were recognized in Europe: L. borealis Atkinson, L. ciliata (Sirodot) De Toni, L. condensata Israelson, L. fluviatilis (Linnaeus) C. Agardh, L. fucina Bory, L. mamillosa Kützing, L. rigida (Sirodot) De Toni and L. sudetica Kützing (Eloranta et al. 2011).

Most common species of the Lemanea genus is L. fluviatilis, which until now was the only species identified in Serbia (Simić 1995; 2002; 2007; Simić & Ranković 1998; Blagojević et al. 2017). The first data on the Lemanea genus in Serbia come from the late 20th century (Simić 1995). The first occurrence of L. fluviatilis was reported in 1991 in the Golema River (as the Crnovrška River; Simić 1995). Between 1991 and 2017, only L. fluviatilis was reported from 10 localities in seven upland and mountain rivers of Eastern (the Golema River, the Svrljiški Timok River, the Resava River and the Dojkinačka River) and Southern (the Vlasina River, the Božica River) Serbia (Simić 1995; 2002; 2007; Simić & Ranković 1998; Blagojević et al. 2017). These localities are characterized by specific ecological conditions (stable substrate in clean, cold, and temperate, fast-flowing, weakly alkaline and well-oxygenated waters). Although most of these habitats are protected to varying degrees, they are still affected by negative human impact (Simić et al. 2010).

Lemanea species are known to be stenovalent in relation to a large number of biotic and abiotic parameters. Any change in environmental conditions can lead to changes in the water regime and changes in ecological conditions in microhabitats where these sensitive species cannot continue to live (Eloranta & Kwandrans 2007; Simić et al. 2010; Eloranta 2019).

There are many factors that threaten habitats of Lemanea species (Eloranta & Kwandrans 2007; Simić et al. 2010). However, a major problem of habitat degradation is the intensive development of hydropower plants (HPPs), which has emerged in recent years. In order to reduce greenhouse gas emissions and mitigate climate change, the European Union established the EU Renewable Energy Directive, with HPPs as the global primary source of renewable energy (Berga 2016). HPPs are under development in all European countries, but the most dynamic development is observed in Central and Western Europe, in the Danube and Balkan regions (Schwarz 2019). Most of the HPPs are small and contribute only marginally to hydropower production (Manzano-Agugliaro et al. 2017). The most significant difference between large and small HPPs is that small HPPs are usually constructed on smaller rivers, unlike large HPPs (Kibler & Tullos 2013). Small HPPs have unavoidable negative environmental impacts, such as river fragmentation, modification of downstream hydromorphology, flow regimes, temperature, sediment transport and deposition (Liermann et al. 2012; Wiatkowski & Tomczyk 2018). The transformation of flowing rivers into standing water can have multifarious effects on primary production and changes in benthic organisms (Wu et al. 2010). Negative ecological consequences of small HPPs are recognized in many countries, resulting in their removal. In the Balkan region, the development of HPPs, especially small HPPs, is increasing. More than 3800 HPPs are planned to be constructed or are currently under construction directly on the mountain, pristine Balkan rivers characterized by the richest biodiversity (Schwarz 2019; Hunđek et al. 2020).

This paper aims to present a review of research on the Lemanea genus in Serbian riverine ecosystems and to provide new data on the diversity of Lemanea species in Serbia, their morphology, distribution and ecology, based on the analysis of 14 populations found in Serbian rivers. Possible factors threatening the habitats of Lemanea species are presented and discussed, including mainly the negative environmental impact of small HPPs.

Materials and methods
Sample collection

Field surveys were conducted at 150 localities in 97 rivers of Western, Southwestern, Eastern and Southern Serbia from April to November in 2017, 2018 and 2019. Twenty mature thalli were collected at each locality where Lemanea taxa were found. In addition to thalli of Lemanea, thalli of other macroalgal aggregations were collected. Samples of algae were collected at a depth ranging from 0 to 50 cm by scraping them from the stony substrate with tweezers. The collected material was immediately preserved with 4% formaldehyde or 96% ethanol. The percentage cover of Lemanea species was assessed by visual analysis for each 1 m section and averaged for 10 m lengths along the riverbed (Necchi & Moreira 1995; Ramirez-Rodriguez et al. 2007). All collected samples are stored in the collection of the Department of Biology and Ecology, Faculty of Science, University of Kragujevac.

Microscopic observation and species identification

Morphological features were analyzed under a Motic BA310 microscope with up to 800× magnification and photographed with BRESSER (9MP) and MicroCamLab. For the identification of Lemanea species, the following morphological and reproductive features were recorded and measured: thalli length, presence of a stalked sterile basal part and its transition into the fertile part of the thallus, presence and frequency of branching, nodal diameter (ND), internodal diameter (ID), nodal/internodal diameter ratio (ND/ID), spermatangial papillae arrangement, length and diameter of carpospores, as well as the presence of the Chantransia stage. Lemanea species were identified according to Kumano (2002), Eloranta & Kwandrans (2007) and Eloranta et al. (2011). Other algae present in the collected samples were identified according to Krammer & Lange-Bertalot (1986, 1991), Komárek & Anagnostidis (1995, 2005), Komárek (2013) and Wehr & Sheath (2003).

Environmental conditions

The type of substrate, current velocity (m s−1), maximum depth and shade were determined at each locality. Environmental conditions were measured according to the American Public Health Association (1995): temperature (°C), pH, conductivity (μS cm−1), water hardness (mg l−1), dissolved oxygen (mg l−1) and nutrient concentration. Nitrogen concentration was determined as ammonia nitrogen NH4-N (mg l−1) and nitrate nitrogen NO3-N (mg l−1), while the concentration of soluble phosphorus was determined as orthophosphate PO4-P (mg l−1) concentration.

Possible threat factors were determined at each locality by visual analysis, as well as according to the Survey of Small Hydropower Plants in the Republic of Serbia (Ministry of Mining and Energy of the Republic of Serbia): 1 – no negative impact, 2 – impact by local population (wastewater, solid waste, traffic), 3 – planned construction of HPP, 4 – small HPP constructed, 5 – planned construction of small HPP.

Literature review

The available literature on the distribution and ecology of the Lemanea genus in Serbia published between 1995 and 2017 was compiled and reviewed.

Results

During field surveys carried out in 2017, 2018, and 2019, a total of 150 riverine locations were studied and thalli of the Lemanea genus were collected from 14 locations in 12 rivers (Fig. 1, Tables 1, 2). Six of them were already known from previous studies (the Golema River, the Dojkinačka River – three localities, the Božica River and the Vlasina River), while eight of them represent new localities in Serbia (the Veljušnica River, the Jelašnica River, the Gradska River, the Božica channel, the Masurica River, the Vuneva River, the Veliki Rzav River and the Mileševka River; Fig. 1). Four taxa were identified at 14 localities: Lemanea fucina, L. rigida, Lemanea sp. and L. fluviatilis. Thalli of L. fucina and L. rigida were recorded in Serbia for the first time. Morphological features of the thalli collected from the Masurica River and the Vuneva River did not match those described in recent identification keys.

Figure 1

Geographical location of Lemanea fucina, Lemanea rigida, Lemanea sp. and Lemanea fluviatilis localities in Serbia

(■) Lemanea fucina: the Veljušnica River (VE); (♣) Lemanea rigida: the Jelašnica River (JR), the Gradska River (GR), the Božica channel (BC); (▲) Lemanea sp.: the Masurica River (MR), the Vuneva River (VU); (●) Lemanea fluviatilis: the Veliki Rzav River (VR), the Mileševka River (MI), the Vlasina River (VL), the Božica River (BR), the Golema River (GO), the Dojkinačka River (DR)

Geographical coordinates and environmental parameters of Lemanea fucina, Lemanea rigida and Lemanea sp. localities in Serbia

SpeciesRiver (population code)/DateGeographical coordinatesAltitude (m)Depth (cm)Substrate typeVelocity (m s−1)Temperature (°C)pHCond. (μS cm−1)Hardness (mg l−1)O2 (mg l−1)NH4 (mg l−1)NO3 (mg l−1)PO4 (mg l−1)Degree of shadeCoverage (%)Associated macroalgaeThreat factors
Lemanea fucinaVeljušnica (VE) 15.08.201843°22′05.7″N 19°54′35.0″E9920stone1.313.98.113201609.87<0.03<4<0.06++20Cladophora glomerata2
Lemanea rigidaJelašnica (JR) 20.08.201942°37′56.9″N 22°07′06.6″E4335–10stone1.517.47.535902809.72<0.03<4<0.06++10Paralemanea sp.2
Gradska River (GR) 26.05.201842°54′07.6″N 22°20′46.3″E5440stone1.814.77.51100509.96<0.03<40.19+++10Nostoc sp.2, 4
Božica channel (BC) 23.07.201942°40′44.8″N 22°21′02.1″E12120–5stone215.67.75102609.66<0.03<4<0.06+++10Audouinella hermannii Hydrurus foetidus Cladophora glomerata2
Lemanea sp.Masurica (MR) 28.05.201842°36′48.5″N 22°13′13.0″E8875–10stone1.511.57.48603010.35<0.03<4<0.06++30/1
Vuneva (VU) 28.05.201842°36′46.7″N 22°13′16.2″E88910stone1.311.27.46703010.41<0.03<4<0.06+7/1

+++ full sunlight; ++ partial shade; + full shade.

1 – no negative impact; 2 – impact by local population (wastewater, solid waste, traffic); 3 – planned construction of HPP; 4 – small HPP constructed; 5 – planned construction of small HPP

Geographical coordinates and environmental parameters of Lemanea fluviatilis localities in Serbia

SpeciesRiver (population code)/DateGeographical coordinatesAltitude (m)Depth (cm)Substrate typeVelocity (m s−1)Temperature (°C)pHCond. (μS cm−1)Hardness (mg l−1)O2 (mg l−1)NH4 (mg l−1)NO3 (mg l−1)PO4 (mg l−1)Degree of shadeCoverage (%)Associated macroalgaeThreat factors
Lemanea fluviatilisVeliki Rzav (VR)* 19.05.201843°45′12.5″N 22°00′12.1″E38950stone2.010.47.982701309.98<0.03<4<0.06+++5Nostoc sp.3
Mileševka (MI)* 06.07.201943°21′58.4″N 19°43′16.9″E5715stone1.615.18.052951509.91<0.03<4<0.06++10Nostoc sp. Cladophora glomerata2
Vlasina (VL) 26.05.201842°51′09.4″N 22°17′02.1″E7300–5stone1.514.17.59904010.1<0.03<4<0.06+++20Nostoc sp. Hydrurus foetidus Cladophora glomerata2, 4, 5
Božica River (BR) 27.05.201842°37′07.0″N 22°24′02.4″E10380stone1.313.37.0880409.35<0.03<40.21+++20Hydrurus foetidus2
Golema River (GO) 30.08.201843°23′44.2″N 22°36′18.8″E9050stone1.513.67.831801009.86<0.03<4<0.06+30/2
Dojkinačka River (DR1) 19.08.201943°15′40.9″N 22°46′50.6″E96010stone2.012.17.3216010010.31<0.03<4<0.06+10/5
Dojkinačka River (DR2) 19.08.201943°15′02.0″N 22°46′32.6″E97210stone1.512.37.2614011010.2<0.03<4<0.06++20/5
Dojkinačka River (DR3) 19.08.201943°15′32.0″N 22°46′37.8″E92410stone1.812.37.2914011010.28<0.03<4<0.06++20/5

new finding

+++ full sunlight; ++ partial shade; + full shade.

1 – no negative impact; 2 – impact by local population (wastewater, solid waste, traffic); 3 – planned construction of HPP; 4 – small HPP constructed; 5 – planned construction of small HPP

Geographical coordinates and environmental parameters of the Lemanea localities are summarized in Tables 1 and 2. Morphological and reproductive features of the identified Lemanea taxa are summarized in Tables 3 and 4.

Morphological and reproductive features of Lemanea fucina, Lemanea rigida and Lemanea sp. from Serbia

SpeciesRiverPlant length (cm)Sterile basal partBranchingNodal diameter (μm)Internodal diameter (μm)ND:IDSpermatangial papillae arrangementCarpospores length (μm)Carpospores diameter (μm)Chantransia
Lemanea fucinaVeljušnica (VE).3.2–8.7gradually expanding into the fertile parttrue/false460–690370–5601.3Protruding; 2–3 in whorls; regular or irregular15.2–19.1 (29.5–48.8)*9.6–13.8 (20.5–42.6)*+
Lemanea rigidaJelašnica (JR)5.3–8.5gradually expanding into the fertile parttrue480–720300–4501.4protruding or flat; 2–3 in whorls; regular or irregular26.8–42.1*19.3–33.2*
Gradska River (GR)5.1–9.25gradually expanding into the fertile parttrue/false410–590300–4301.4protruding or flat; 3 in whorls; regular or irregular13.6–20.510–15.2
Božica channel (BC)4.6–9.7gradually expanding into the fertile parttrue/false490–750400–5801.3protruding or flat; 2–3 in whorls; regular or irregular30.7–42.1*20.5–30.7*
Lemanea sp.Masurica (MR)2.3–5imperceptibly expanding into the fertile parttrue360–530290–4401.3plane, rarely protruding; 2–3 in whorls; regular or irregular12.1–22.56.2–13.5
Vuneva (VU)2.6–5.6imperceptibly expanding into the fertile parttrue380–520300–4401.3plane, rarely protruding; 2–3 in whorls; regular or irregular12–226–13.7

+ present; – not present

mature carpospores

Morphological and reproductive features of Lemanea fluviatilis from Serbia

SpeciesRiver (population code)Plant length (cm)Sterile basal partBranchingNodal diameter (μm)Internodal diameter (μm)ND:IDSpermatangial papillae arrangementCarpospores length (μm)Carpospores diameter (μm)Chantransia
Lemanea luviatilisVeliki Rzav (VR)2.5–5.2abruptly expanding into the fertile parttrue/false400–570290–4401.5patches; 2–3 in whorls; regular or irregular21.7–31.212.1–17.5
Mileševka (MI)4.5–11.5abruptly or gradually expanding into the fertile parttrue/false450–590300–4301.4protruding; 2–4 in whorls; regular or irregular35.8–50.5*20.5–38.5*+
Vlasina (VL)4.9–12.2abruptly expanding into the fertile parttrue/false550–680400–5501.3patches; 2–3 in whorls; regular or irregular20.5–33.713.6–18.8
Božica River (BR)4.7–7.1abruptly expanding into the fertile parttrue460–650350–5201.3patches; 2–3 in whorls; regular or irregular23.5–33.5*15.2–20.5*+
Golema River (GO)4.7–6.2abruptly expanding into the fertile parttrue/false500–620360–4501.3patches; 2–4 in whorls; regular or irregular20.5–26.210.8–18.5
Dojkinačka River (DR1, DR2, DR3)5.4–9.3abruptly expanding into the fertile partno510–780360–5801.4patches; 2–3 in whorls; regular or irregular29.5–41*18.5–25.3*+

+ present; – not present

mature carpospores

Our research covered all previously known localities of Lemanea species (10 localities) in Serbia. We found that this genus disappeared from four of them (two localities in the Resava River, one locality in the Svrljiški Timok River and one locality in the Dojkinačka River). Geographical coordinates and environmental data from previous research on Lemanea are presented in Table 5.

Geographical coordinates and environmental parameters of the previously described Lemanea fluviatilis localities from Serbia

River (population code)/DateGeographical coordinatesAltitude (m)Depth (cm)Substrate typeVelocity (m s−1)Temperature (°C)pHConductivity (μS cm−1)O2 (mg l−1)N (mg l−1)P (mg l−1)Degree of shadeAssociated macroalgaeReference
Golema River (as the Crnovrška River) 06.1991/1250/stone1.429.07.6/13.60.450.2++Chamaesiphon polonicus Phormidium favosum Tapinothrix janthina (as Homoeothrix janthina)Simić 1995
Svrljiški Timok River 06.1991/400/stone114.78.35/10.680.450.1+++Chantransia pygmaea Vaucheria sp. Cladophora glomerata Stigeoclonium elongatum Ulothrix zonataSimić 2002
Resava River 01.05.2003/450//1.5////////Simić 2007
Resava River 12.04.2004/800//1.110.07.81608.594.70.058//Simić 2007
Božica River 15.08.2004/1100//1.113.87.1708.514.60.443//Simić 2007
Vlasina River 15.08.2004/1000///////////Simić 2007
Dojkinačka River 26.07.201043°15′43.3″N 22°46′23.2″E101530//12.57.0//////Blagojević et al. 2017
Dojkinačka River 25.07.201043°15′24.5″N 22°46′31.3″E100030//15.07.5//////Blagojević et al. 2017
Dojkinačka River 25.07.201043°15′02.0″N 22°46′32.6″E97230//16.08.0//////Blagojević et al. 2017
Dojkinačka River 25.07.201043°15′32.0″N 22°46′37.8″E92430//17.07.0//////Blagojević et al. 2017

+++ full sunlight; ++ partial shade

Hypertrophies of tissue at the base of spermatangia, in the form of papules with regular or irregular edges, were observed along thalli collected from the Božica River, the Dojkinačka River, the Veljušnica River, the Jelašnica River and the Gradska River.

Lemanea fucina Bory 1808

Homotypic synonym: Sacheria fucina (Bory) Sirodot

Heterotypic synonym: Lemanea mamillosa var. fucina Kützing

Morphological features

Thalli grew in tufts. Almost every collected thallus was tattered and small in size, very dark green or black in color, and covered with the epiphyte Leptolyngbya foveolarum (Gomont) Anagnostidis and Komárek. The length of such thalli ranged from 3.2 to 4.5 cm (Fig. 2: 1, Table 3). False branching was observed in most of the regenerated parts of such thalli (Table 3). Few thalli collected from the same population were delicate, light green with clearly visible abundant branching (Fig. 2: 1, Table 3) and without epiphytes. The length of such thalli ranged from 7.6 to 8.7 cm (Fig. 2: 1, Table 3). The thalli gradually narrowed toward the base and continued into the sterile basal part (Fig. 2: 2, Table 3). The sterile basal part was 0.8–2.85 cm long, thin, slightly stalked. The nodal diameter (ND) ranged from 460 to 690 μm and the internodal diameter (ID) ranged from 370 to 560 μm (Fig. 2: 3, Table 3). The ratio of nodal diameter to internodal diameter (ND/ID) was 1.3 (Table 3). Spermatangial papillae were protruding, 2–3 in whorls, regularly or irregularly distributed in the nodal region (Fig. 2: 3, Table 3). The carposporophyte zone was usually cylindrical. Young carpospores occurred in strings, cylindrical (length 15.2–19.1 μm, width 9.6–13.8 μm; Table 3). Mature carpospores were oval to oblong (length 29.5–48.8 μm, width 20.5–42.6 μm; Table 3). The Chantransia stage was present in places where the thallus was torn (Table 3), branched unilaterally and alternately. Monospores were not observed. The sporophyte develops from the Chantransia stage.

Figure 2

Morphological and reproductive features of Lemanea fucina: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Lemanea rigida (Sirodot) De Toni 1897

Basionym: Sacheria rigida Sirodot

Heterotypic synonym: Lemanea fucina var. rigida Atkinson

Morphological features

Thalli grew in tufts. Their length ranged from 4.6 to 9.7 cm (Fig. 3: 1, Table 3). They were dark green in color. The thalli gradually narrowed into the base and continued into the sterile basal part (Fig. 3: 2, Table 3). The sterile basal part was 0.4–1.6 cm long, thin, slightly stalked. True branching was present, but not abundant (Table 3). False branching was observed in the regenerated parts of the thallus in places where it was torn (the Gradska River and the Božica channel; Table 3). The nodal diameter (ND) ranged from 410 to 750 μm and the internodal diameter (ID) ranged from 300 to 580 μm (Fig. 3: 3, Table 3). The nodal to internodal diameter ratio (ND/ID) ranged from 1.3 to 1.4 (Table 3). Spermatangial papillae were protruding or flat, 3 in whorls, regularly or irregularly distributed in the nodal region (Fig. 3: 3, Table 3). The carposporophyte zone was usually cylindrical. Young carpospores were in strings, oval to oblong (length 13.6–20.5 μm, width 10–15.2 μm; the Gradska River; Table 3). Oval to oblong mature carpospores (length 26.8–42.1 μm, width 19.3–33.2 μm) were observed in specimens from the Jelašnica River and the Božica channel (Table 3). The Chantransia stage was not observed (Table 3).

Figure 3

Morphological and reproductive features of Lemanea rigida: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Lemanea sp.
Morphological features

Thalli grew in tufts. Their length ranged from 2.3 to 5.6 cm (Fig. 4: 1, Table 3). They were olive green to dark green, curved, slender. They indistinctly tapered toward the base and continued into the sterile basal part (Table 3). The sterile basal part was 0.5–0.9 cm long, thin, unstalked. True branching was present (Table 3). The nodal diameter (ND) ranged from 360 to 530 μm and the internodal diameter (ID) ranged from 290 to 440 μm (Fig. 4: 2, Table 3). The nodal to internodal diameter ratio (ND/ID) was 1.3 (Table 3). Spermatangial papillae were flat, slightly or rarely prominently protruding, 2–3 in whorls, regularly or rarely irregularly distributed in the nodal region (Fig. 4: 3, Table 3). The carposporophyte zone was usually cylindrical. Young carpospores were in strings, ellipsoidal to oblong (length 12–22.5 μm, width 6–13.7 μm; Table 3). Mature carpospores and the Chantransia stage were not observed (Table 3).

Figure 4

Morphological and reproductive features of Lemanea sp.: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Lemanea fluviatilis (Linnaeus) C.Agardh 1811

Basionym: Conferva fluviatilis Linnaeus

Homotypic synonyms: Conferva fluviatilis Linnaeus, Chantransia fluviatilis (Linnaeus) De Candolle, Sacheria fluviatilis (Linnaeus) Sirodot

Heterotypic synonyms: Chantransia nigricans De Candolle, Lemanea corallina Bory, Lemanea fucina var. subtilis Atkinson

Morphological features

Thalli grew in tufts. Their length ranged from 2.5 to 12.2 cm (Fig. 5: 1, Table 4). The thalli were yellowish olive or olive green in color. They abruptly narrowed toward the base and continued into the sterile basal part (Fig. 5: 2, Table 4). The sterile basal part was 0.5–1.5 cm long, thin, stalked. True branching was sparse; false branching was also observed (Table 4). The nodal diameter (ND) ranged from 400 to 780 μm and the internodal diameter (ID) ranged from 290 to 580 μm (Fig. 5: 3, Table 4). The nodal to internodal diameter ratio (ND/ID) ranged from 1.3 to 1.5 (Table 4). Spermatangial papillae occurred in patches, 2–4 in whorls, regularly or irregularly distributed in the nodal region (Fig. 5: 3, Table 4). The carposporophyte zone was usually cylindrical. Young carpospores were in strings, cylindrical (length 20.5–33.7 μm, width 10.8–18.8 μm; Table 4). Mature carpospores were oval to oblong (length 23.5–50.5 μm, width 15.2–38.5 μm; Table 4). The Chantransia stage was observed in specimens collected in the Mileševka River, the Božica River and the Dojkinačka River (Table 4). It branched unilaterally and alternately. Monospores were not observed.

Figure 5

Morphological and reproductive features of Lemanea fluviatilis: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Distribution and ecology

The most common species in the collected samples was L. fluviatilis, found at eight localities. Lemanea rigida was found at three localities, L. fucina at one locality, while Lemanea sp. was found at two localities. Thalli of L. fluviatilis were collected from the Veliki Rzav River, the Mileševka River (Southwestern Serbia), the Golema River and from three localities in the Dojkinačka River (Eastern Serbia), the Božica River and the Vlasina River (Southern Serbia; Fig. 1, Table 2). Thalli of L. fucina were collected from the Veljušnica River (Southwestern Serbia), while thalli of L. rigida were collected from the Jelašnica River, the Gradska River and the Božica channel (Southern Serbia; Fig. 1, Table 1). Thalli of Lemanea sp. were collected from the Masurica River and the Vuneva River (Southern Serbia) (Fig. 1, Table 1). These Lemanea taxa were found at altitudes ranging from 389 m to 1212 m in similar specific environmental conditions (Tables 1, 2). Thalli of L. fucina, L. rigida, Lemanea sp. and L. fluviatilis were found in turbulent lotic waters with current velocity ranging from 1.3 to 2 m s−1, on the stony substrate at depths ranging from 0 to 50 cm, in full sunlight, in partial or full shade (Tables 1, 2). The water from which thalli were collected was temperate (water temperature ranging from 11.2°C to 17.4°C), soft or moderately hard (water hardness ranging from 30 mg l−1 to 280 mg l−1), well-oxygenated (from 9.66 mg l−1 to 10.41 mg l−1) and weakly alkaline (pH from 7.46 to 8.11), with low, moderate or high conductivity (from 60 μS cm−1 to 590 μS cm−1) and low content of inorganic nutrients (Tables 1, 2). Only the concentration of orthophosphates was slightly increased at the localities in the Gradska River and the Božica River (Table 1).

Thalli of Nostoc sp. grew together with thalli of L. rigida (the Gradska River) and L. fluviatilis (the Veliki Rzav River, the Mileševka River and the Vlasina River). The alga Cladophora glomerata (L.) Kützing grew together with thalli of L. fucina (the Veljušnica River), L. rigida (the Božica channel) and L. fluviatilis (the Mileševka River and the Vlasina River), whereas thalli of Paralemanea sp. grew together with thalli of L. rigida (the Jelašnica River). The red alga Audouinella hermannii (Roth) Duby and the chrysophycean alga Hydrurus foetidus (Villars) Trevisan were found together with thalli of L. rigida in the Božica channel. The chrysophycean alga H. foetidus was also found growing together with thalli of L. fluviatilis in the Vlasina River.

Epiphytes were found on thalli of Lemanea fucina, L. rigida and L. fluviatilis. The cyanobacterial species Chamaesiphon rostafinskii Hansgirg, L. foveolarum, L. notata (Schmidle) Anagnostidis and Komárek and the diatom taxa Gomphonella olivacea (Hornemann) Rabenhorst and Navicula sp. developed as epiphytes on L. fucina thalli, while the cyanobacterial species L. foveolarum, the red alga A. hermannii and the diatom taxa Cymbella sp., G. olivacea, Gomphonema capitatum Ehrenberg, Navicula sp. and Planothidium lanceolatum (Brébisson ex Kützing) Lange-Bertalot developed as epiphytes on L. rigida thalli. The cyanobacterial species Ch. rostafinskii and the diatom species Cocconeis placentula Ehrenberg and G. olivacea developed as epiphytes on L. fluviatilis thalli.

Threat factors

It was observed during the field surveys that only the Masurica and Vuneva river localities were not affected by negative anthropogenic impact. Whereas all other localities were found to be affected by threat factors (Tables 1, 2).

Discussion

Our research confirms the difficulties in the identification of Lemanea species based on the morphological and reproductive features described in the available literature. Kučera & Marvan (2004) speculated that small variations in diacritic features could be a consequence of the variation in age and maturity of thalli.

The above-mentioned difficulties in identifying Lemanea species are particularly evident for L. fucina and L. mamillosa. In the literature, these two species were described under different synonyms, and the morphological and reproductive differences between them are often not clear enough (Kumano 2002; Eloranta et al. 2011). Simić & Đorđević (2011) observed congruence with the basic diagnostic features of these two species in the material collected from the same locality in the Tara River during the same period of the life cycle, but in different years. The identification of thalli collected from the Veljušnica River was quite difficult due to the small size of collected thalli, which is probably a consequence of grazing by herbivorous macroinvertebrates. Grazing can also explain damage to almost every collected thallus. According to Caro-Borrero and Carmona-Jiménez (2016), red algae can be used as a food source by herbivorous macroinvertebrates, which leads to the damage of thalli and increased release and germination of carpospores and new gametophytes.

False branching was observed on thalli of L. fucina, L. rigida and L. fluviatilis in places where thalli were torn. A similar phenomenon was described in Paralemanea mexicana (Kützing) M.L.Vis and R.G.Sheath (Vis & Sheath 1992; Carmona & Necchi 2002), based on which this species was distinguished from other Paralemanea species. False branching was also described in P. annulata (Kützing) M.L.Vis and R.G.Sheath and P. catenata (Kützing) M.L.Vis and R.G.Sheath (Simić & Đorđević 2017). Some authors suggested that false branching is apparently exclusive to P. mexicana (Carmona et al. 2013). However, we disagree that those newly formed branches are taxonomic features.

Since identification of Lemanea species based on morphological and reproductive features is difficult and insufficient, morphological analysis combined with molecular analysis is required for reliable identification.

Lemanea fluviatilis is the most common species of Lemanea. It has been studied by many authors and its ecology and distribution are fairly well researched. The species occurs mainly in the Northern Hemisphere, in Europe, North America and Asia (Vis, Sheath 1992; Eloranta et al. 2011; Ganesan et al. 2018). Based on previously published data as well as this paper, L. fluviatilis is the most frequent species of Lemanea in Serbia (Simić 1995; 2002; 2007; Simić & Ranković 1998; Blagojević et al. 2017). Lemanea fucina and L. rigida occur in Europe (Eloranta et al. 2011), while L. fucina is also recorded in North America (Vis & Sheath 1992).

Data on the geographical distribution and ecology of the Lemanea genus in the Balkan region are very scarce. With the exception of Serbia, rare Lemanea species were reported from Albania (Kashta & Miho 2016), Bulgaria (Temniskova et al. 2008), Croatia (Koletić et al. 2020) and Montenegro (Simić & Djordjević 2011; Simić et al. 2019). Lemanea fucina was recorded in Croatia (Koletić et al. 2020) and Montenegro (Simić & Djordjević 2011; Simić et al. 2019), L. rigida in Croatia (Koletić et al. 2020), while L. fluviatilis was also recorded in Croatia (Koletić et al. 2020). Our collections of L. fucina and L. rigida represent the first occurrence of these rare species in Serbia and contribute to the knowledge of their distribution and ecology in the Balkan region.

In general, Lemanea species occur in turbulent flowing waters. They colonize stable and hard substrates, such as stones, rocks, but also concrete blocks, bridge pillars and rarely wood, and occur in full sunlight or partially shaded rivers with high to moderate flow rates (Vis & Sheath 1992; Simić 1995; 2002; 2007; Eloranta & Kwandrans 1996; 2007; Chemeris & Bobrov 2009; Eloranta et al. 2016; Eloranta 2019). In our study, all thalli were collected from stony substrates, at places characterized by high flow rates (from 1.3 m s−1 to 2 m s−1). Thalli of L. fluviatilis were found in full sunlight (the Veliki Rzav River, the Vlasina River and the Božica River), as well as in partial (the Mileševka River and the Dojkinačka River) and full shade (the Golema River and the Dojkinačka River). Thalli of L. fucina were found in partial shade, thalli of L. rigida were found in partial shade (the Jelašnica River) and full sunlight (the Gradska River and the Božica channel), while thalli of Lemanea sp. were found in full (the Vuneva River) and partial shade (the Masurica River).

Thalli of the Lemanea genus can be found at a depth of more than 100 cm, but they reach their maximum growth and development in early spring and summer when the water level is low and algae often remain on the rock surface within the contact zone between water and air (Vis & Sheath 1992; Eloranta & Kwandran 2007; Simić 1995; 2002; 2007). In our study, thalli of the Lemanea genus were found at a depth ranging from 0 to 50 cm.

Our research confirmed that Lemanea species prefer cold and temperate, soft or moderately hard, neutral or slightly alkaline, well-oxygenated and oligotrophic water (Vis & Sheath 1992; Simić 1995; 2002; 2007; Eloranta & Kwandrans 1996; 2007; Eloranta et al. 2016; Eloranta 2019). According to Dell'Uomo (1991), however, they can also be found in waters with moderate pollution.

Because Lemanea species are adapted to specific environmental conditions, any direct or indirect negative anthropogenic impact threatens their survival. Intensification of negative anthropogenic impact on the habitats of Lemanea species has led to Lemanea species being protected in many countries (Siemińska 1992; Temniskova et al. 2008; Hyvärinen et al. 2019). In Serbia, the Lemanea genus is not legally protected. According to the Code on declaration and protection of strictly protected and protected wild species of plants, animals and fungi, Appendix 1 (Institute for Nature Conservation of Serbia 5/2010, 47/2011, 32/2016, 98/2016), ten species of Rhodophyta from the genera Bangia, Batrachospermum, Hildenbrandia, Paralemanea, and Thorea are protected in Serbia.

Previous findings on the occurrence of L. fluviatilis in the Svrljiški Timok River (Simić 2002), the Resava River (two localities; Simić 2007) and the Dojkinačka River (Lilina česma locality; Blagojević et al. 2017) were not confirmed by this research. The locality in the Svrljiški Timok River was affected by eutrophication. One locality at the Resava River was destroyed in a wildfire, while the negative impact of the local community (wastewater, solid waste) was observed at the other locality in the same river. The riverbed at one locality in the Dojkinačka River was dry during the sampling period.

Habitats of the new Lemanea species are exposed to the impact of the local community (wastewater, solid waste, traffic), and several of them may be threatened by the development of HPPs, usually the derivative type of small HPPs.

The construction of all planned small HPPs in Serbia will provide an insignificant energy balance, but environmental damage to these ecosystems will be immeasurable (Ristić et al. 2018). Since all parts of riverine ecosystems are interconnected, any disturbance to one part of the system will trigger a response in most parts of the system (Wu et al. 2010). The significant impact of small HPPs on riverine ecosystems is particularly pronounced in periods of moderate flows, when minimum water flow prescribed by the law does not discharge into the river (Wu et al. 2010; Fijko et al. 2017). Wu et al. (2010) researched and proved the significant effects of small HPPs on the benthic algal community in terms of different physical and chemical conditions between control and dammed sites, a significant increase in chlorophyll-a concentration, total algal density and major impact on the overall benthic algal community in dry periods.

Perhaps the most striking negative ecological impact of small HPPs is observed at the multiple installation level. The presence of multiple installations reduces conductivity in rivers and impedes the dispersal ability of freshwater organisms (Kibler & Tullos 2013). The cumulative effects of small HPPs are observed on the Vlasina River, where nine small HPPs are already constructed and several are planned for construction (Ministry of Mining and Energy of Republic of Serbia). During our field surveys, the watercourse downstream from the constructed small HPPs was devasted and no benthic algae were observed.

Since Lemanea species were found at only 14 locations in Serbian riverine ecosystems affected by the above-mentioned threat factors, their protection and protection of their habitats is necessary. The construction of HPPs, especially small HPPs, planned in pristine upland-mountain Serbian rivers will destroy most of the Lemanea habitats along with the habitats of strictly protected Rhodophyta species.

Figure 1

Geographical location of Lemanea fucina, Lemanea rigida, Lemanea sp. and Lemanea fluviatilis localities in Serbia(■) Lemanea fucina: the Veljušnica River (VE); (♣) Lemanea rigida: the Jelašnica River (JR), the Gradska River (GR), the Božica channel (BC); (▲) Lemanea sp.: the Masurica River (MR), the Vuneva River (VU); (●) Lemanea fluviatilis: the Veliki Rzav River (VR), the Mileševka River (MI), the Vlasina River (VL), the Božica River (BR), the Golema River (GO), the Dojkinačka River (DR)
Geographical location of Lemanea fucina, Lemanea rigida, Lemanea sp. and Lemanea fluviatilis localities in Serbia(■) Lemanea fucina: the Veljušnica River (VE); (♣) Lemanea rigida: the Jelašnica River (JR), the Gradska River (GR), the Božica channel (BC); (▲) Lemanea sp.: the Masurica River (MR), the Vuneva River (VU); (●) Lemanea fluviatilis: the Veliki Rzav River (VR), the Mileševka River (MI), the Vlasina River (VL), the Božica River (BR), the Golema River (GO), the Dojkinačka River (DR)

Figure 2

Morphological and reproductive features of Lemanea fucina: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3
Morphological and reproductive features of Lemanea fucina: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Figure 3

Morphological and reproductive features of Lemanea rigida: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3
Morphological and reproductive features of Lemanea rigida: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Figure 4

Morphological and reproductive features of Lemanea sp.: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3
Morphological and reproductive features of Lemanea sp.: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Figure 5

Morphological and reproductive features of Lemanea fluviatilis: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3
Morphological and reproductive features of Lemanea fluviatilis: 1 – habit; 2 – transition of the sterile basal part into the fertile part; 3 – nodal and internodal diameter, spermatangial papillae arrangement. Scale bars: 1 cm for plate 1; 100 μm for plates 2 and 3

Geographical coordinates and environmental parameters of Lemanea fluviatilis localities in Serbia

Species River (population code)/Date Geographical coordinates Altitude (m) Depth (cm) Substrate type Velocity (m s−1) Temperature (°C) pH Cond. (μS cm−1) Hardness (mg l−1) O2 (mg l−1) NH4 (mg l−1) NO3 (mg l−1) PO4 (mg l−1) Degree of shade Coverage (%) Associated macroalgae Threat factors
Lemanea fluviatilis Veliki Rzav (VR)* 19.05.2018 43°45′12.5″N 22°00′12.1″E 389 50 stone 2.0 10.4 7.98 270 130 9.98 <0.03 <4 <0.06 +++ 5 Nostoc sp. 3
Mileševka (MI)* 06.07.2019 43°21′58.4″N 19°43′16.9″E 571 5 stone 1.6 15.1 8.05 295 150 9.91 <0.03 <4 <0.06 ++ 10 Nostoc sp. Cladophora glomerata 2
Vlasina (VL) 26.05.2018 42°51′09.4″N 22°17′02.1″E 730 0–5 stone 1.5 14.1 7.59 90 40 10.1 <0.03 <4 <0.06 +++ 20 Nostoc sp. Hydrurus foetidus Cladophora glomerata 2, 4, 5
Božica River (BR) 27.05.2018 42°37′07.0″N 22°24′02.4″E 1038 0 stone 1.3 13.3 7.08 80 40 9.35 <0.03 <4 0.21 +++ 20 Hydrurus foetidus 2
Golema River (GO) 30.08.2018 43°23′44.2″N 22°36′18.8″E 905 0 stone 1.5 13.6 7.83 180 100 9.86 <0.03 <4 <0.06 + 30 / 2
Dojkinačka River (DR1) 19.08.2019 43°15′40.9″N 22°46′50.6″E 960 10 stone 2.0 12.1 7.32 160 100 10.31 <0.03 <4 <0.06 + 10 / 5
Dojkinačka River (DR2) 19.08.2019 43°15′02.0″N 22°46′32.6″E 972 10 stone 1.5 12.3 7.26 140 110 10.2 <0.03 <4 <0.06 ++ 20 / 5
Dojkinačka River (DR3) 19.08.2019 43°15′32.0″N 22°46′37.8″E 924 10 stone 1.8 12.3 7.29 140 110 10.28 <0.03 <4 <0.06 ++ 20 / 5

Geographical coordinates and environmental parameters of the previously described Lemanea fluviatilis localities from Serbia

River (population code)/Date Geographical coordinates Altitude (m) Depth (cm) Substrate type Velocity (m s−1) Temperature (°C) pH Conductivity (μS cm−1) O2 (mg l−1) N (mg l−1) P (mg l−1) Degree of shade Associated macroalgae Reference
Golema River (as the Crnovrška River) 06.1991 / 1250 / stone 1.42 9.0 7.6 / 13.6 0.45 0.2 ++ Chamaesiphon polonicus Phormidium favosum Tapinothrix janthina (as Homoeothrix janthina) Simić 1995
Svrljiški Timok River 06.1991 / 400 / stone 1 14.7 8.35 / 10.68 0.45 0.1 +++ Chantransia pygmaea Vaucheria sp. Cladophora glomerata Stigeoclonium elongatum Ulothrix zonata Simić 2002
Resava River 01.05.2003 / 450 / / 1.5 / / / / / / / / Simić 2007
Resava River 12.04.2004 / 800 / / 1.1 10.0 7.8 160 8.59 4.7 0.058 / / Simić 2007
Božica River 15.08.2004 / 1100 / / 1.1 13.8 7.1 70 8.51 4.6 0.443 / / Simić 2007
Vlasina River 15.08.2004 / 1000 / / / / / / / / / / / Simić 2007
Dojkinačka River 26.07.2010 43°15′43.3″N 22°46′23.2″E 1015 30 / / 12.5 7.0 / / / / / / Blagojević et al. 2017
Dojkinačka River 25.07.2010 43°15′24.5″N 22°46′31.3″E 1000 30 / / 15.0 7.5 / / / / / / Blagojević et al. 2017
Dojkinačka River 25.07.2010 43°15′02.0″N 22°46′32.6″E 972 30 / / 16.0 8.0 / / / / / / Blagojević et al. 2017
Dojkinačka River 25.07.2010 43°15′32.0″N 22°46′37.8″E 924 30 / / 17.0 7.0 / / / / / / Blagojević et al. 2017

Geographical coordinates and environmental parameters of Lemanea fucina, Lemanea rigida and Lemanea sp. localities in Serbia

Species River (population code)/Date Geographical coordinates Altitude (m) Depth (cm) Substrate type Velocity (m s−1) Temperature (°C) pH Cond. (μS cm−1) Hardness (mg l−1) O2 (mg l−1) NH4 (mg l−1) NO3 (mg l−1) PO4 (mg l−1) Degree of shade Coverage (%) Associated macroalgae Threat factors
Lemanea fucina Veljušnica (VE) 15.08.2018 43°22′05.7″N 19°54′35.0″E 992 0 stone 1.3 13.9 8.11 320 160 9.87 <0.03 <4 <0.06 ++ 20 Cladophora glomerata 2
Lemanea rigida Jelašnica (JR) 20.08.2019 42°37′56.9″N 22°07′06.6″E 433 5–10 stone 1.5 17.4 7.53 590 280 9.72 <0.03 <4 <0.06 ++ 10 Paralemanea sp. 2
Gradska River (GR) 26.05.2018 42°54′07.6″N 22°20′46.3″E 544 0 stone 1.8 14.7 7.51 100 50 9.96 <0.03 <4 0.19 +++ 10 Nostoc sp. 2, 4
Božica channel (BC) 23.07.2019 42°40′44.8″N 22°21′02.1″E 1212 0–5 stone 2 15.6 7.7 510 260 9.66 <0.03 <4 <0.06 +++ 10 Audouinella hermannii Hydrurus foetidus Cladophora glomerata 2
Lemanea sp. Masurica (MR) 28.05.2018 42°36′48.5″N 22°13′13.0″E 887 5–10 stone 1.5 11.5 7.48 60 30 10.35 <0.03 <4 <0.06 ++ 30 / 1
Vuneva (VU) 28.05.2018 42°36′46.7″N 22°13′16.2″E 889 10 stone 1.3 11.2 7.46 70 30 10.41 <0.03 <4 <0.06 + 7 / 1

Morphological and reproductive features of Lemanea fucina, Lemanea rigida and Lemanea sp. from Serbia

Species River Plant length (cm) Sterile basal part Branching Nodal diameter (μm) Internodal diameter (μm) ND:ID Spermatangial papillae arrangement Carpospores length (μm) Carpospores diameter (μm) Chantransia
Lemanea fucina Veljušnica (VE). 3.2–8.7 gradually expanding into the fertile part true/false 460–690 370–560 1.3 Protruding; 2–3 in whorls; regular or irregular 15.2–19.1 (29.5–48.8)* 9.6–13.8 (20.5–42.6)* +
Lemanea rigida Jelašnica (JR) 5.3–8.5 gradually expanding into the fertile part true 480–720 300–450 1.4 protruding or flat; 2–3 in whorls; regular or irregular 26.8–42.1* 19.3–33.2*
Gradska River (GR) 5.1–9.25 gradually expanding into the fertile part true/false 410–590 300–430 1.4 protruding or flat; 3 in whorls; regular or irregular 13.6–20.5 10–15.2
Božica channel (BC) 4.6–9.7 gradually expanding into the fertile part true/false 490–750 400–580 1.3 protruding or flat; 2–3 in whorls; regular or irregular 30.7–42.1* 20.5–30.7*
Lemanea sp. Masurica (MR) 2.3–5 imperceptibly expanding into the fertile part true 360–530 290–440 1.3 plane, rarely protruding; 2–3 in whorls; regular or irregular 12.1–22.5 6.2–13.5
Vuneva (VU) 2.6–5.6 imperceptibly expanding into the fertile part true 380–520 300–440 1.3 plane, rarely protruding; 2–3 in whorls; regular or irregular 12–22 6–13.7

Morphological and reproductive features of Lemanea fluviatilis from Serbia

Species River (population code) Plant length (cm) Sterile basal part Branching Nodal diameter (μm) Internodal diameter (μm) ND:ID Spermatangial papillae arrangement Carpospores length (μm) Carpospores diameter (μm) Chantransia
Lemanea luviatilis Veliki Rzav (VR) 2.5–5.2 abruptly expanding into the fertile part true/false 400–570 290–440 1.5 patches; 2–3 in whorls; regular or irregular 21.7–31.2 12.1–17.5
Mileševka (MI) 4.5–11.5 abruptly or gradually expanding into the fertile part true/false 450–590 300–430 1.4 protruding; 2–4 in whorls; regular or irregular 35.8–50.5* 20.5–38.5* +
Vlasina (VL) 4.9–12.2 abruptly expanding into the fertile part true/false 550–680 400–550 1.3 patches; 2–3 in whorls; regular or irregular 20.5–33.7 13.6–18.8
Božica River (BR) 4.7–7.1 abruptly expanding into the fertile part true 460–650 350–520 1.3 patches; 2–3 in whorls; regular or irregular 23.5–33.5* 15.2–20.5* +
Golema River (GO) 4.7–6.2 abruptly expanding into the fertile part true/false 500–620 360–450 1.3 patches; 2–4 in whorls; regular or irregular 20.5–26.2 10.8–18.5
Dojkinačka River (DR1, DR2, DR3) 5.4–9.3 abruptly expanding into the fertile part no 510–780 360–580 1.4 patches; 2–3 in whorls; regular or irregular 29.5–41* 18.5–25.3* +

American Public Health Association. (1995). Standard methods for examination of Water and Wastewater, 19th ed.. Washington, DC: Port City Press. American Public Health Association 1995 Standard methods for examination of Water and Wastewater 19th ed. Washington, DC Port City Press Search in Google Scholar

Berga, L. (2016). The role of hydropower in climate change mitigation and adaptation: a review. Engineering 2: 313–318. DOI: 10.1016/J.ENG.2016.03.004. BergaL. 2016 The role of hydropower in climate change mitigation and adaptation: a review Engineering 2 313 318 10.1016/J.ENG.2016.03.004 Open DOISearch in Google Scholar

Blagojević, A., Subakov Simić, G., Blaženčić, J., Ilić, M., Petrović, J. et al. (2017). First record of Paralemanea torulosa (Roth) Sheath & A.R. Sherwood and new findings of Lemanea fluviatilis (Linnaeus) C. Ag. and Hildenbrandia rivularis (Liebmann) J. Agardh (Rhodophyta) in Serbia. Botanica Serbica 41(1): 55–63. DOI: 10.5281/zenodo.454096. BlagojevićA. Subakov SimićG. BlaženčićJ. IlićM. PetrovićJ. 2017 First record of Paralemanea torulosa (Roth) Sheath & A.R. Sherwood and new findings of Lemanea fluviatilis (Linnaeus) C. Ag. and Hildenbrandia rivularis (Liebmann) J. Agardh (Rhodophyta) in Serbia Botanica Serbica 41 1 55 63 10.5281/zenodo.454096 Open DOISearch in Google Scholar

Carmona, J.J. & Necchi, O.Jr. (2002). Taxonomy and distribution of Paralemanea (Lemaneaceae, Rhodophyta) in Central Mexico. Cryptogamie Algol. 23: 39–49. DOI: 10.1016/S0181-1568(02)85006-1. CarmonaJ.J. NecchiO.Jr. 2002 Taxonomy and distribution of Paralemanea (Lemaneaceae, Rhodophyta) in Central Mexico Cryptogamie Algol. 23 39 49 10.1016/S0181-1568(02)85006-1 Open DOISearch in Google Scholar

Carmona, J.J., Bojorge, M. & Ramirez, R.R. (2013). Phenology of Paralemanea mexicana (Batrachospermales, Rhodophyta) in high-altitude stream in central Mexico. Phycol Res. 62: 86–93. DOI: 10.1111/pre.12042. CarmonaJ.J. BojorgeM. RamirezR.R. 2013 Phenology of Paralemanea mexicana (Batrachospermales, Rhodophyta) in high-altitude stream in central Mexico Phycol Res. 62 86 93 10.1111/pre.12042 Open DOISearch in Google Scholar

Caro-Borrero, A. & Carmona-Jiménez, J. (2016). Associations Between Macroinvertebrates and Paralemanea mexicana, an endemic freshwater red alga from a Mountain River in Central Mexico. Neotrop Entomol. 45(6): 665–674. DOI: 10.1007/s13744-016-0420-z. Caro-BorreroA. Carmona-JiménezJ. 2016 Associations Between Macroinvertebrates and Paralemanea mexicana, an endemic freshwater red alga from a Mountain River in Central Mexico Neotrop Entomol 45 6 665 674 10.1007/s13744-016-0420-z 27394719 Open DOISearch in Google Scholar

Chemeris, E.V. & Bobrov, A.A. (2009). Records of Rhodophyta species in rivers of the upper Volga region and adjacent areas. Botanitsetskij Journal 94: 1568–1583. ChemerisE.V. BobrovA.A. 2009 Records of Rhodophyta species in rivers of the upper Volga region and adjacent areas Botanitsetskij Journal 94 1568 1583 Search in Google Scholar

Dell'Uomo, A. (1991). Use of benthic macroalgae for monitoringrivers in Italy. In B.A. Whitton, E. Rott & G. Friedrich (Eds), Use of algae for monitoring river (pp. 129–138). Innsbruck: Universität of Innsbruck, Institut für Botanik. Dell'UomoA. 1991 Use of benthic macroalgae for monitoringrivers in Italy In WhittonB.A. RottE. FriedrichG. (Eds), Use of algae for monitoring river 129 138 Innsbruck Universität of Innsbruck, Institut für Botanik Search in Google Scholar

Eloranta, P. (2019). Freshwater red algae in Finland. Plant and Fungal Systematics 64(1): 4–51. DOI: 10.2478/pfs-2019-0006. ElorantaP. 2019 Freshwater red algae in Finland Plant and Fungal Systematics 64 1 4 51 10.2478/pfs-2019-0006 Open DOISearch in Google Scholar

Eloranta, P. & Kwandrans, J. (1996). Distribution and ecology of freshwater red algae (Rhodophyta) in some central Finnish rivers. Nordic Journal of Botany 16: 107–117. ElorantaP. KwandransJ. 1996 Distribution and ecology of freshwater red algae (Rhodophyta) in some central Finnish rivers Nordic Journal of Botany 16 107 117 10.1111/j.1756-1051.1996.tb00220.x Search in Google Scholar

Eloranta, P. & Kwandrans, J. (2007). Freshwater red algae (Rhodophyta). Identification guide to European taxa, particularly to those in Finland. Finland: Norrlinia. ElorantaP. KwandransJ. 2007 Freshwater red algae (Rhodophyta) Identification guide to European taxa, particularly to those in Finland. Finland Norrlinia Search in Google Scholar

Eloranta, P., Kwandrans, J. & Kusel-Fetzmann, E. (2011). Rhodophyceae and Phaeophyceae. In B. Budel, G. Gartner, L. Krienitz, H.R. Preisig & M. Schagerl (Eds.), Freshwater flora of Central Europe (pp. 1–155). Heidelberg: Spectrum Akademischer Verlag. ElorantaP. KwandransJ. Kusel-FetzmannE. 2011 Rhodophyceae and Phaeophyceae In BudelB. GartnerG. KrienitzL. PreisigH.R. SchagerlM. (Eds.), Freshwater flora of Central Europe 1 155 Heidelberg Spectrum Akademischer Verlag Search in Google Scholar

Eloranta, P., Eloranta, A. & Perämäki, P. (2016). Intensive study of freshwater red algae (Rhodophyta) in Finland. Fottea 16(1): 122–132. DOI: 10.5507/fot.2015.025. ElorantaP. ElorantaA. PerämäkiP. 2016 Intensive study of freshwater red algae (Rhodophyta) in Finland Fottea 16 1 122 132 10.5507/fot.2015.025 Open DOISearch in Google Scholar

Fijko, R. & Zeleňáková, M. (2017). Impact of small hydropower plant on the biodiversity of the selected area. In 10th International Conference “Environmental Engineering”, 27–28 April 2017 (pp. 1–6). Lithuania: Vilnius Gediminas Technical University. DOI: 10.3846/enviro.2017.077. FijkoR. ZeleňákováM. 2017 Impact of small hydropower plant on the biodiversity of the selected area In 10th International Conference “Environmental Engineering” 27–28 April 2017 1 6 Lithuania Vilnius Gediminas Technical University 10.3846/enviro.2017.077 Open DOISearch in Google Scholar

Ganesan, E.K., West, J.A. & Necchi, O.Jr. (2018). A catalogue and bibliography of non-marine (freshwater and estuarine) Rhodophyta (red algae) in India. Phytotaxa 364(1): 1–48. DOI: 10.11646/phytotaxa.364.1. GanesanE.K. WestJ.A. NecchiO.Jr. 2018 A catalogue and bibliography of non-marine (freshwater and estuarine) Rhodophyta (red algae) in India Phytotaxa 364 1 1 48 10.11646/phytotaxa.364.1 Open DOISearch in Google Scholar

Guiry, M.D. & Guiry G.M. (2020). AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Available from: http://algaebase.org (accessed 22 June 2020). GuiryM.D. GuiryG.M. 2020 AlgaeBase. World-wide electronic publication National University of Ireland Galway Available from: http://algaebase.org (accessed 22 June 2020). Search in Google Scholar

Hunđek, H., Žganec, K. & Pusch M.T. (2020). A review of hydropower dams in Southeast Europe – distribution, trends and availability of monitoring data using the example of a multinational Danube catchment subarea. Renewable and Sustainable Energy Reviews 117: 1–11. DOI: 10.1016/j.rser.2019.109434. HunđekH. ŽganecK. PuschM.T. 2020 A review of hydropower dams in Southeast Europe – distribution, trends and availability of monitoring data using the example of a multinational Danube catchment subarea Renewable and Sustainable Energy Reviews 117 1 11 10.1016/j.rser.2019.109434 Open DOISearch in Google Scholar

Hyvärinen, E., Juslén, A., Kemppainen, E., Udström, A. & Liukko, U-M. (Eds.) (2019). The 2019 Red List of Finnish Species. Ministry of the Environment & Finnish Environmental Institute. Helsinki. (In Finnish) HyvärinenE. JuslénA. KemppainenE. UdströmA. LiukkoU-M. (Eds.) 2019 The 2019 Red List of Finnish Species Ministry of the Environment & Finnish Environmental Institute Helsinki. (In Finnish) Search in Google Scholar

Kashta, L. & Miho, A. (2016). The more frequently occurring macroalgae in Albanian running waters, BSHN 21/2016: 31–40. KashtaL. MihoA. 2016 The more frequently occurring macroalgae in Albanian running waters BSHN 21/2016 31 40 Search in Google Scholar

Kibler, K.M. & Tullos, D.D. (2013). Cumulative biophysical impact of small and large hydropower development in Nu River, China. Water Resources Research 49: 3104–3118. DOI: 10.1002/wrcr.20243. KiblerK.M. TullosD.D. 2013 Cumulative biophysical impact of small and large hydropower development in Nu River, China Water Resources Research 49 3104 3118 10.1002/wrcr.20243 Open DOISearch in Google Scholar

Koletić, N., Alegro, A., Rimac, A., Vuković, N. & Šegota V. (2020). Catalogue of Croatian Freshwater Rhodophytes. Phytotaxa 434(2): 151–169. DOI: 10.11646/phytotaxa.434.2.2. KoletićN. AlegroA. RimacA. VukovićN. ŠegotaV. 2020 Catalogue of Croatian Freshwater Rhodophytes Phytotaxa 434 2 151 169 10.11646/phytotaxa.434.2.2 Open DOISearch in Google Scholar

Komárek, J. (2013). Cyanoprokaryota 3. Teil: Heterocytous Genera. In B. Büdel, G. Gärtner, L. Krienitz & M. Schagerl (Eds), Süßwasserflora von Mitteleuropa 19/3 (pp. 1–1130). Heidelberg, Berlin: Springer Spektrum Verlag. KomárekJ. 2013 Cyanoprokaryota 3. Teil: Heterocytous Genera In BüdelB. GärtnerG. KrienitzL. SchagerlM. (Eds), Süßwasserflora von Mitteleuropa 19/3 1 1130 Heidelberg, Berlin Springer Spektrum Verlag 10.1007/978-3-8274-2737-3_1 Search in Google Scholar

Komárek, J. & Anagnostidis, K. (1999). Cyanoprokaryota 1. Teil: Chroococcales. In H. Ettl, G. Gärtner, H. Heynig & D. Mollenhauer (Eds), Süßwasserflora von Mitteleuropa 19/1 (pp. 1–548). Heidelberg, Berlin: Spektrum Akademischer Verlag. KomárekJ. AnagnostidisK. 1999 Cyanoprokaryota 1. Teil: Chroococcales In EttlH. GärtnerG. HeynigH. MollenhauerD. (Eds), Süßwasserflora von Mitteleuropa 19/1 1 548 Heidelberg, Berlin Spektrum Akademischer Verlag Search in Google Scholar

Komárek, J. & Anagnostidis, K. (2005). Cyanoprokaryota 2. Teil: Oscillatoriales - In B. Büdel, G. Gärtner, L. Krienitz & M. Schagerl (Eds), Süβwasserflora von Mitteleuropa 19/2 (pp. 1–759). Heidelberg: Elsevier. KomárekJ. AnagnostidisK. 2005 Cyanoprokaryota 2. Teil: Oscillatoriales In BüdelB. GärtnerG. KrienitzL. SchagerlM. (Eds), Süβwasserflora von Mitteleuropa 19/2 1 759 Heidelberg Elsevier Search in Google Scholar

Krammer, K. & Lange-Bertalot, H. (1986). Bacillariophyceae. 1. Teil: Naviculaceae. In H. Ettl, J. Gerloff, H. Heynig & D. Mollenhauer (Eds), Süsswasserflora von Mitteleuropa 2/1 (pp. 1–876). Jena: G. Fischer Verlag. KrammerK. Lange-BertalotH. 1986 Bacillariophyceae. 1. Teil: Naviculaceae In EttlH. GerloffJ. HeynigH. MollenhauerD. (Eds), Süsswasserflora von Mitteleuropa 2/1 1 876 Jena G. Fischer Verlag Search in Google Scholar

Krammer, K. & Lange-Bertalot, H. (1991). Bacillariophyceae. 4. Teil: Achnanthaceae. In H. Ettl, G. Gartner, J. Gerloff, H. Heynig & D. Mollenhauer (Eds), Süsswasserflora von Mitteleuropa 2/4 (pp. 1–437). Stuttgart: G. Fischer Verlag. KrammerK. Lange-BertalotH. 1991 Bacillariophyceae. 4. Teil: Achnanthaceae In EttlH. GartnerG. GerloffJ. HeynigH. MollenhauerD. (Eds), Süsswasserflora von Mitteleuropa 2/4 1 437 Stuttgart G. Fischer Verlag Search in Google Scholar

Kumano, S. (2002). Freshwater Red Algae of the World. Bristol: Biopress Ltd. KumanoS. 2002 Freshwater Red Algae of the World Bristol Biopress Ltd. Search in Google Scholar

Kučera, P. & Marvan, P. (2004). Taxonomy and distribution of Lemanea and Paralemanea (Lemaneaceae, Rhodophyta) in the Czech Republic. Preslia 76:163–174. KučeraP. MarvanP. 2004 Taxonomy and distribution of Lemanea and Paralemanea (Lemaneaceae, Rhodophyta) in the Czech Republic Preslia 76 163 174 Search in Google Scholar

Liermann, C.R., Nilsson, C., Robertson, J. & Ng, R.Y. (2012). Implications of dam obstruction for global freshwater fish diversity. BioScience 62: 539–548. DOI: 10.1525/BIO.2012.62.6.5. LiermannC.R. NilssonC. RobertsonJ. NgR.Y. 2012 Implications of dam obstruction for global freshwater fish diversity BioScience 62 539 548 10.1525/BIO.2012.62.6.5 Open DOISearch in Google Scholar

Manzano-Agugliaro, F., Taher, M., Zapata-Sierra, A., Juaidi, A. & Montoya, F.G. (2017). An overview of research and energy evolution for small hydropower in Europe. Renewable and Sustainable Energy Reviews 75: 476–489. DOI: 10.1016/j.rser.2016.11.013. Manzano-AgugliaroF. TaherM. Zapata-SierraA. JuaidiA. MontoyaF.G. 2017 An overview of research and energy evolution for small hydropower in Europe Renewable and Sustainable Energy Reviews 75 476 489 10.1016/j.rser.2016.11.013 Open DOISearch in Google Scholar

Ministry of Mining and Energy of Republic of Serbia. Survey of small hydropower plants in Serbia. Available from: (http://mhe.mre.gov.rs/). Ministry of Mining and Energy of Republic of Serbia Survey of small hydropower plants in Serbia Available from: (http://mhe.mre.gov.rs/). Search in Google Scholar

Necchi, O.Jr. & Moreira, J.C.L. (1995). Longitudinal distribution of macroalgae in two tropical lotic ecosystems from southeastern Brazil. Arch Hydrobiol. 135: 113–128. NecchiO.Jr. MoreiraJ.C.L. 1995 Longitudinal distribution of macroalgae in two tropical lotic ecosystems from southeastern Brazil Arch Hydrobiol. 135 113 128 10.1127/archiv-hydrobiol/135/1995/113 Search in Google Scholar

Institute for Nature Conservation of Serbia. (5/2010, 47/2011, 32/2016, 98/2016). Code on declaration and protection of strictly protected and protected wild species of plants, animals and fungi. Serbia: Official Gazette of the Republic of Serbia. Institute for Nature Conservation of Serbia (5/2010, 47/2011, 32/2016, 98/2016). Code on declaration and protection of strictly protected and protected wild species of plants, animals and fungi Serbia Official Gazette of the Republic of Serbia Search in Google Scholar

Ramirez-Rodriguez, R., Carmona, J. & Martorell, C. (2007). Microhabitat and morphometric variation in two species of Prasiola (Prasiolales, Chlorophyta) from stream in central Mexico. Aquat Ecol. 41: 161–168. DOI: 10.1007/s10452-006-9068-9. Ramirez-RodriguezR. CarmonaJ. MartorellC. 2007 Microhabitat and morphometric variation in two species of Prasiola (Prasiolales, Chlorophyta) from stream in central Mexico Aquat Ecol. 41 161 168 10.1007/s10452-006-9068-9 Open DOISearch in Google Scholar

Ristić, R., Malušević, I., Polovina, S., Milčanović, V. & Radić, B. (2018). Small hydropower plants – derivation type: insignificant energy benefit and immeasurable environmental damage. Vodoprivreda 50(294–296): 311–317. (English summary) RistićR. MaluševićI. PolovinaS. MilčanovićV. RadićB. 2018 Small hydropower plants – derivation type: insignificant energy benefit and immeasurable environmental damage Vodoprivreda 50 294–296 311 317 (English summary) Search in Google Scholar

Schwarz, U. (2019). Hydropower pressure on European rivers: The story in numbers. For FLUVIUS, WWF, RiverWatch, EuroNatur & GEOTA. SchwarzU. 2019 Hydropower pressure on European rivers: The story in numbers For FLUVIUS, WWF, RiverWatch, EuroNatur & GEOTA. Search in Google Scholar

Siemińska, J. (1992). List of threatened plants in Poland (2nd edition). In K. Zarzycky, W. Wojewoda & Z. Heinrich (Eds), List of threatened plants in Poland (pp. 7–19). Poland: Polish Academy of Sciences, W. Szafer Institute of Botany. SiemińskaJ. 1992 List of threatened plants in Poland 2nd edition In ZarzyckyK. WojewodaW. HeinrichZ. (Eds), List of threatened plants in Poland 7 19 Poland Polish Academy of Sciences, W. Szafer Institute of Botany Search in Google Scholar

Simić, S. (1995). Benthic algae communities of the Trgoviški Timok. Master's thesis, University of Belgrade, Belgrade, Serbia. (In Serbian). SimićS. 1995 Benthic algae communities of the Trgoviški Timok Master's thesis, University of Belgrade Belgrade, Serbia (In Serbian). Search in Google Scholar

Simić, S. (2002). Macroalgae in streams of hill-mountain areas of Serbia. Doctoral dissertation, University of Belgrade, Belgrade, Serbia. (In Serbian). SimićS. 2002 Macroalgae in streams of hill-mountain areas of Serbia Doctoral dissertation, University of Belgrade Belgrade, Serbia (In Serbian). Search in Google Scholar

Simić, S. (2007). Morphological and ecological characteristics of rare and endangered species Lemanea fluviatilis (L.) C. Ag. (Lemaneaceae, Rhodophyta) on new localities in Serbia. Krag. J. Sci. 29: 97–106. SimićS. 2007 Morphological and ecological characteristics of rare and endangered species Lemanea fluviatilis (L.) C. Ag. (Lemaneaceae, Rhodophyta) on new localities in Serbia Krag. J. Sci. 29 97 106 Search in Google Scholar

Simić, S. & Ranković, B. (1998). New data on the distribution, morphology and ecology of red algae (Rhodophyta) in rivers of Serbia. Arch. Biol. Sci. 50(1): 43–50. SimićS. RankovićB. 1998 New data on the distribution, morphology and ecology of red algae (Rhodophyta) in rivers of Serbia Arch. Biol. Sci. 50 1 43 50 Search in Google Scholar

Simić, S. & Djordjević, N. (2011). Lemanea fucina Bory, 1808 (Lemaneaceae, Rhodophyta), a rare species with a variable morphology: first record in the Republic of Montenegro. Arch. Biol. Sci. 63(2): 511–515. DOI: 10.2298/ABS1102511S. SimićS. DjordjevićN. 2011 Lemanea fucina Bory, 1808 (Lemaneaceae, Rhodophyta), a rare species with a variable morphology: first record in the Republic of Montenegro Arch. Biol. Sci. 63 2 511 515 10.2298/ABS1102511S Open DOISearch in Google Scholar

Simić, S.B. & Đorđević, N.B. (2017). Morphology, distribution and ecology of the freshwater red algae Paralemanea (Batrachospermaceae, Batrachospermales, Rhodophyta) in Serbia. Arch. Biol. Sci. 69(1): 167–174. DOI: 10.2298/ABS160211093S. SimićS.B. ĐorđevićN.B. 2017 Morphology, distribution and ecology of the freshwater red algae Paralemanea (Batrachospermaceae, Batrachospermales, Rhodophyta) in Serbia Arch. Biol. Sci. 69 1 167 174 10.2298/ABS160211093S Open DOISearch in Google Scholar

Simić, S., Pantović, N. & Vasiljević, B. (2010). Factors threatening the habitats of rare species of Rhodophyta in Serbia. In Conference on water observation and information system for decision suport, Balwois, 25–29 May 2010 (pp. 440–451). Republic of Macedonia, Ohrid: University St. Kliment Ohridski, Hydrobiological Institute Naum. SimićS. PantovićN. VasiljevićB. 2010 Factors threatening the habitats of rare species of Rhodophyta in Serbia Conference on water observation and information system for decision suport, Balwois 25–29 May 2010 440 451 Republic of Macedonia, Ohrid University St. Kliment Ohridski, Hydrobiological Institute Naum Search in Google Scholar

Simić, B.S., Đorđević B.N. & Mitrović, B.A. (2019). Review of the research on red algae (Rhodophyta) in freshwater ecosystems in Montenegro. International Conference “Adriatic Biodiversity Protection”, 07–11 April 2019 (p. 113). Montenegro, Kotor: University of Montenegro, Institute of Marine Biology. SimićB.S. ĐorđevićB.N. MitrovićB.A. 2019 Review of the research on red algae (Rhodophyta) in freshwater ecosystems in Montenegro International Conference “Adriatic Biodiversity Protection” 07–11 April 2019 113 Montenegro, Kotor University of Montenegro, Institute of Marine Biology Search in Google Scholar

Temniskova, D., Stoyneva, P.M. & Kirjakov, K.I. (2008). Red List of the Bulgarian algae. I Macroalgae. Phytol Balc. 14(2): 193–206. TemniskovaD. StoynevaP.M. KirjakovK.I. 2008 Red List of the Bulgarian algae. I Macroalgae Phytol Balc. 14 2 193 206 Search in Google Scholar

Vis, L. & Sheath, R.G. (1992). Systematics of the freshwater red algal family Lemaneaceae in North America. Phycologia 31(2): 164–179. DOI: 10.2216/i0031-8884-31-2-164.1. VisL. SheathR.G. 1992 Systematics of the freshwater red algal family Lemaneaceae in North America Phycologia 31 2 164 179 10.2216/i0031-8884-31-2-164.1 Open DOISearch in Google Scholar

Wehr, J.D. & Sheath, RG. (2003). Freshwater Algae of North America Ecology and Classification. USA: Academic Press. WehrJ.D. SheathRG. 2003 Freshwater Algae of North America Ecology and Classification USA Academic Press Search in Google Scholar

Wiatkowski, M. & Tomczyk, P. (2018). Comparative assessment of the hydromorphological status of the rivers Odra, Bystrzyca, and sleza using the RHS, LAWA, QBR, and HEM methods above and below the hydropower plants. Water 10: 1–16. DOI: 10.3390/w10070855. WiatkowskiM. TomczykP. 2018 Comparative assessment of the hydromorphological status of the rivers Odra, Bystrzyca, and sleza using the RHS, LAWA, QBR, and HEM methods above and below the hydropower plants Water 10 1 16 10.3390/w10070855 Open DOISearch in Google Scholar

Wu, N.C., Jiang, W.X., Fu, X.C., Zhou, S.C., Li, F.Q. et al. (2010). Temporal impacts of a small hydropower plant on benthic algal community. Fundam. Appl. Limnol. 177(4): 257–266. DOI: 10.1127/1863-9135/2010/0177-0257. WuN.C. JiangW.X. FuX.C. ZhouS.C. LiF.Q. 2010 Temporal impacts of a small hydropower plant on benthic algal community Fundam. Appl. Limnol. 177 4 257 266 10.1127/1863-9135/2010/0177-0257 Open DOISearch in Google Scholar

Recommended articles from Trend MD