Acta Botanica 2-2015.indd ACTA BOT. CROAT. 74 (2), 2015 253 Acta Bot. Croat. 74 (2), 253–264, 2015 CODEN: ABCRA 25 ISSN 0365-0588 eISSN 1847-8476 DOI: 10.1515/botcro-2015-0027 First report of Navicula jakovljevicii Hustedt (Bacillariophyta) from Hungary: distribution, comparative morphology and a related species VIKTÓRIA B-BÉRES1*, ISTVÁN BÁCSI2, ENIKŐ T-KRASZNAI1, ZSUZSANNA KÓKAI1, KRISZTINA BUCZKÓ3 1 Environmental Protection and Nature Conservation Authority, Trans-Tisza Region, Debrecen, Hatvan u. 16. H-4025 Hungary 2 University of Debrecen, Department of Hydrobiology, Debrecen, Egyetem tér 1. H-4032 Hungary 3 Hungarian Natural History Museum, Budapest, Könyves Kálmán krt. 40. H-1476 Hungary Abstract – In Hungary Navicula jakovljevicii was fi rstly recorded in biofi lm of Elodea nut- tallii in 2005 in an oxbow of the catchment area of the River Danube. Subsequently, in 2006, N. jakovljevicii was also found in the same oxbow on reed stems as well. In the fol- lowing years it appeared in another oxbow, suggesting an expanding distribution in the trib- utaries of the Danube in Hungary. The Hungarian population can be characterised as having mixed morphological features in comparison with other known N. jakovljevicii populations of Europe. When the morphological study was expanded, a similar, but 'giant form' was detect ed in fossil material. We found similarities and a possible connection between N. ja- kovljevicii and Navicula lucida, a diatom taxon described from a Neogene deposit in the Carpathian Basin. Despite the morphological similarities in the shape, apices, striae pattern and raphe structure of these two species, there are signifi cant differences in valve dimen- sions: the valves of N. lucida are larger and more heavily silicifi ed than N. jakovljevicii. Keywords: biofi lm, Danube, Elodea nuttalli, Navicula jakovljevicii, Navicula lucida, ox- bow, Pantocsek collection Introduction Navicula jakovljevicii Hustedt (1945: 931) was described from the Balkan Peninsula in 1945 by Friedrich Hustedt (HUSTEDT 1945). For a long time it seemed that the distribution of this diatom species was restricted to South Europe (PLENKOVIĆ-MORAJ 1995). The taxo- * Corresponding author, e-mail: beres.viktoria@gmail.com B-BÉRES V., BÁCSI I., T-KRASZNAI E., KÓKAI Z., BUCZKÓ K. 254 ACTA BOT. CROAT. 74 (2), 2015 nomical position of the species is uncertain. According to the earlier published morphologi- cal details (REICHARDT 1992, LANGE-BERTALOT 2001, LEVKOV et al. 2005) neither the raphe structure (raphe fi ssures weakly lateral, slightly curved) nor the striae pattern (the striae consist of poroids that are elongated externally but alveolate internally) are the same as the members of Navicula s. str. Furthermore a hole can be detected on the valve apex, which is an unusual feature. LANGE-BERTALOT (2001) indicated in the Monograph of diatoms of Europe, that some fossil species from the upper Tertiary period bear the same structures as Navicula jakov- ljevicii. He mentioned Köpecz (Căpeni, Romania today) material, and published two pic- tures (Plate 62 fi gs 1–2) as Navicula (?nov.) spec. from this locality. The legends of these fi gures are the following: Köpecz, southern Carpatians. The structural pattern conforms to the recent Navicula jakovljevicii, and appears like a 'giant form' of this species (LANGE- BERTALOT 2001 p. 360). The Hungarian Natural History Museum holds the József Panto- csek diatom collection, where – among many others – diatom samples from the Carpathians are wel l represented, including samples form Köpecz (PANTOCSEK 1892, 1905, BUCZKÓ 2012). An obvious endeavour was to compare the recent Navicula jakovljevicii with other ancient Navicula taxa from the Köpecz material and try to fi nd this 'giant form'. Due to the hydrological impacts of the Bős/Gabčikovo dam, a low water fl ow condition was formed both in the main river channel of the Danube and in the smaller arms (OTHELO- VA and VALACHOVIC 2002, RÁTH et al. 2003, HAJÓSY 2012). Based on these facts, a macro- and microfl ora monitoring project (including diatom monitoring also) was conducted be- tween 1994 and 2009 on the River Danube, on its river branches and on the oxbows. The aim of that study was to follow up the effects of the Bős/Gabčikovo dam on the macro- and microfl ora assemblages of the so-called Szigetköz region (HAJÓSY 2012). It was observed, that the changing water discharge and fl ow conditions allowed appearances and distribution of adventive and invasive macrophytes, as Elodea canadensis Michaux (1803: 20) and Elo- dea nuttallii (Planchon 1848: 86) H. St John (1920: 29) (RÁTH et al. 2003, OTHELOVA and VALACHOVIC 2003, KIRÁLY et al. 2007, KOČIĆ et al. 2014). Although macrophytes could serve as ‘spreading transport substrate’ for invasive species, diatoms among them (HOR- VÁTH and LAMBERTI 1997), the fi rst Hungarian observation of a characteristic diatom taxa during the counting procedure in 2005 was surprising. This diatom taxa was identifi ed as Navicula jakovljevicii. The main aims of the present study were (i) to report for the fi rst time observation of Navicula jakovljevicii in Hungary; (ii) to compare the morphological features of the Hun- garian N. jakovljevicii population with other known populations of the species; (iii) to re- port the observation of fossil analogues of Navicula jakovljevicii in Miocene material and (iv) to give a possible explanation of the recent observation and spread of N. jakovljevicii in Hungary. Material and methods Sampling localities Szigetköz is a major island of the Danube, harbouring a complex system of habitats. It is situated in northwest Hungary, where the river enters the Carpathian Basin (Fig. 1). Here, the fast fl owing river slows down, deposits the gravel carried from the Alps, divides into many smaller arms turning into a braided channel. Diatom samples were collected between DISTRIBUTION AND COMPARATIVE MORPHOLOGY OF NAVICULA JAKOVLJEVICII ACTA BOT. CROAT. 74 (2), 2015 255 1994 and 2009 on the River Danube and in its catchment area twice a year (Fig. 1). Sam- ples were collected from different macrophytes of sixteen sampling locations (Fig. 1). Dur- ing the sixteen years, more than 1300 samples were collected and analysed. Nearly 300,000 valves were identifi ed from the samples. Sample preparation Diatom samples were prepared using standard digestion procedures (BATTARBEE 1986). Aliquot-evaporated suspensions were embedded in Zrax. At least 400 valves were counted from each sample using a light microscope (LM) (LEICA DM LB2 with 100 HCX PLAN APO objective). Light microscopic pictures were taken by Fujifi lm Digital Camera FinePix S2 Pro and later by VSI–3.OM(H) digital camera. For scanning electron microscopic (SEM) analyses, cleaned samples were air–dried on an aluminium stub. Coating with gold– palladium was accomplished using a XC7620 Mini Sputter Coater for 120 s at 16 mA. A Hitachi S–2600N SEM operated at 20 kV and 5–8 mm distance was used. Morphological terminology follows BARBER and HAWORTH (1981) and ROUND et al. (1990). Valve measure- ments were made from digital images using the camera software. The following materials were examined and presented in this paper: raw materials and permanent slides of the Hungarian Natural History Museum BP 2007/72; BP 2007/73; Pan- tocsek diatom collection Köpecz material (new permanent slides and stubes for SEM were made from dried diatom sample no BP-88, and Bibarczfalva no BP-22). Results In Hungary Navicula jakovljevicii was fi rst recorded in autumn of 2005 in an oxbow at Ásványráró (Fig. 1). The substrate of the biofi lm was the waterweed Elodea nuttallii. Elo- dea nuttallii was present also in the following three years in this oxbow en masse. In 2006 N. jakovljevicii was also found on reed stems in the same oxbow, as well as on the Elodea Fig. 1. The sample locations of hydrobiological monitoring and the occurrences of Navicula jakov- ljevicii (arrows) in the Szigetköz section of the River Danube. Ásványráró (EOV X: 535520 EOV Y: 279130; and EOV X: 535570 EOV Y: 278990); Cikolasziget (EOV X: 525150 EOV Y: 290300). B-BÉRES V., BÁCSI I., T-KRASZNAI E., KÓKAI Z., BUCZKÓ K. 256 ACTA BOT. CROAT. 74 (2), 2015 species. The diatom appeared in another oxbow in Szigetköz on E. nuttallii in 2008. Al- though the diatom species had moved upwards in the catchment area of Danube, its relative abundance was low in every sample, never reaching 3%. Altogether N. jakovljevicii was found only at three sampling sites from the sixteen sites, it was recorded continuously from 2005 until the end of the monitoring in 2009. The recent distribution of the species is shown on On-line Supplement Fig. 1. A detailed morphological description about this characteris- tic species for comparison with other known populations (HUSTEDT 1945, REICHARDT 1992, LEVKOV et al. 2005) is given below. Morphological observations of Navicula jakovljevicii Light microscopy Valves are lanceolate to elliptic-lanceolate with obtusely to broadly rounded ends, 32– 53 μm long, 7–8.7 μm broad (Pl. 1, Figs. 1–7). Raphe fi ssures are weakly lateral. Axial area is narrow, linear, central area is small, weakly asymmetrically rounded. Striae are moder- ately lateral, parallel to weakly convergent at the ends; there are 14–17 striae in 10 μm (Pl. 1, Figs. 1–7). Scanning electron microscopy Raphe fi ssures are distinctly lateral, narrower to the secondary side of the valve, slightly expanded at the proximal part. The proximal raphe endings externally are forked (Pl. 2, Figs. 1–4; Pl. 3, Figs. 1, 3), a silicate tongue divides the raphe terminal. Lineolae are nar- row, elongated, 29–32 in 10 μm. The alveoli are partly occluded on the valve interior (Pl. 2, Fig. 5). The distal raphe ends straight (Pl. 2, Figs. 1–2) or bent to the secondary side (Pl. 2, Fig. 4) and has a well close to the valve ends (Pl. 2, Figs. 1–4; Pl. 3, Fig. 4). Internally, a hole can be detected on the valve apex (Pl. 2, Fig. 5; Pl. 3, Fig. 2). Internally, the distal ra- phe ends are lateral, close to each other (Pl. 3, Fig. 5). The mantle is narrow (Pl. 3, Fig. 6). Pl. 1. Figs.1–7: Navicula jakovljevicii light microscopy (LM) micrographs of type population in the Ásványráró section of the Danube, collected from Elodea nuttallii (sample BP 2007/73). Scale bar represents 10 μm. DISTRIBUTION AND COMPARATIVE MORPHOLOGY OF NAVICULA JAKOVLJEVICII ACTA BOT. CROAT. 74 (2), 2015 257 A related Navicula species from Tertiary diatom deposits (Navicula lucida Pantocsek 1892: tab. 18, fi g. 264) Based on the indication of LANGE-BERTALOT (2001) the Köpecz and Bibarczfalva mate- rials were reinvestigated and some valves of a characteristic, long diatom were found in the samples that are reminiscent of the published pictures in the Monograph of diatoms of Eu- rope (LANGE-BERTALOT 2001 Plate 62 fi gs 1, 2). We identifi ed this diatom species as Navic- ula lucida Pantocsek (1892, 1905: 73; Plate 4, fi g.1). This species was very rare, altogether twelve valves having been documented. The Latin diagnosis (PANTOCSEK 1905) refers to only one valve that is 192 μm long and 19 μm wide. The striae number is 15–16 in 10 μm; they are slightly radial in the middle but almost through parallel along the valves. It was found in the Tertiary, in the Miocene, in fresh water, at localities close to Köpecz and Bodos by Pantocsek. Morphological observations of Navicula lucida Light microscopy Valves are lanceolate, gradually tapering to the apex. The ends of these valves are ob- tusely rounded. The lengths are 110–200 μm (n = 10), the breadths are 15–22 μm. Raphe is Pl. 2. Figs. 1–5: Navicula jakovljevicii scanning electron micrographs (SEM) of the population from Elodea nuttallii (sample 2007/73); Figs. 1–2: external view of entire valves; Fig. 3: oblique position showing the girdle bands; Fig. 4: broken valve; Fig. 5: internal detail of a broken valve. Scale bars represent 10 μm. B-BÉRES V., BÁCSI I., T-KRASZNAI E., KÓKAI Z., BUCZKÓ K. 258 ACTA BOT. CROAT. 74 (2), 2015 distinctly lateral, outer fi ssure curved distinctly towards the central pores. Axial area is moderately narrow and linear, central area is slightly elliptic. Striae are almost parallel, 14–16 in 10 μm; lineolae hardly distinct in LM (Pl. 4, Fig. 2). Scanning electron microscopy Raphe is lateral; externally the central raphe endings are distinctly forked (Pl. 4, Fig. 2; Pl. 5, Fig. 1) just as in N. jakovljevicii (Pl. 2, Figs. 1–4; Pl. 3, Figs. 1, 3). Lineolae are nar- row, elongated, 34–38 in 10 μm. The alveoli are partly occluded on the valve interior (Pl. 4, Fig. 4). Externally, the distal raphe ends turn to the girdle (Pl. 4, Fig. 3; Pl. 5, Fig. 3). Inter- nally, the proximal raphe endings are close to each other (Pl. 5, Fig. 2). Internally, there is an expansion on the proximal part of the raphe fi ssure (Pl. 5, Fig. 2). There is a hole on the apex close to the valve end (Pl. 5, Fig. 4). Discussion Taxonomical remarks on Navicula jakovljevicii and its distribution In the original description by HUSTEDT (1945), N. jakovljevicii was characterized by 32–60 μm in length, 8–11 μm in width and 16–18 striae in 10 μm. REICHARDT (1992) found Pl. 3. Figs: 1–6: Navicula jakovljevicii scanning electron micrographs (SEM) of the population from Elodea nuttallii (sample 2007/73); Figs. 1, 3: External detail of the central area with the proximal raphe endings and the typical ornamentation, note the forked central raphe ends; Fig. 2: internal detail of a valve apex showing a hole; Fig. 4: external detail of a valve apex showing the turning raphe end; Fig. 5: internal detail of the central area; Fig. 6: external detail of a frustulum apex in oblique view showing the mantle elements. Scale bars represent 2 μm. DISTRIBUTION AND COMPARATIVE MORPHOLOGY OF NAVICULA JAKOVLJEVICII ACTA BOT. CROAT. 74 (2), 2015 259 Pl. 4. Figs. 1–4: Navicula lucida; Fig. 1: iconotype, reprint from Pantocsek 1892; Fig. 2: light mi- croscopy (LM) micrograph from Köpecz (Romania), Miocene; Figs. 3–4: scanning electron micrographs (SEM), Fig. 3: external but oblique view of a whole frustule, Fig. 4: internal view. Scale bar for LM is 10 μm; on SEM bars are 50 μm. Pl. 5. Figs. 1–4: Details of Navicula lucida valves. Fig. 1: external view of central area with the characteristic forked central raphe endings; Fig. 2: internal details of central area. Fig. 3: ex- ternal view of a valve apex. Fig. 4: internal view of a valve apex with hole. Scale bars repre- sent 5 μm. B-BÉRES V., BÁCSI I., T-KRASZNAI E., KÓKAI Z., BUCZKÓ K. 260 ACTA BOT. CROAT. 74 (2), 2015 three, slightly different, populations in Lake Zug, in the River Krka and in the Plitvice Lakes. The population found in Lake Zug was slightly thinner (8.4–9.7 μm in width) and smaller (32.9–53.0 μm in length), moreover there were fewer striae (14–15 in 10 μm) than in the form described by HUSTEDT. In contrast, valves from the River Krka were character- ized by being 39–85 μm in length and 8.8–11.7 μm in width. The characteristics of the valves from populations originating in the the Plitvice Lakes were completely in the middle range. Subsequently, LEVKOV et al. (2005) published a detailed morphometric analysis of N. jakovljevicii populations from Nidze Mountain and Lake Ohrid. They found that at least two different populations could be distinguished: the fi rst, N. jakovljevicii morphotype 1, is similar to HUSTEDT’s (1945) description as regards the number of striae in 10 μm (16–18) and the presence of a longitudinal band, but has a greater length (50–80 μm). The second, N. jakovljevicii morphotype 2, has smaller valves (30–50 μm), an indistinct longitudinal band and considerably fewer striae in 10 μm (12–14). The lengths of the valves of the Hungarian populations were partly similar to the transi- tional forms described by HUSTEDT (1945), and partly to the populations from Lake Zug (REICHARDT 1992). The numbers of striae of individuals from Hungary were the closest to the original description (HUSTEDT 1945). Navicula jakovljevicii was primarily known from southern, south-east, and central Eu- rope (Lake Ohrid – JURILJ 1954, Lake Zug, River Krka and Plitvice Lakes – REICHARDT 1992, France – COSTE and ECTOR 2000, Transylvania in fossil deposit – LANGE-BERTALOT 2001, Nidze Mountain and Lake Ohrid – LEVKOV et al. 2003, Macedonia – SMITH and SMITH 2003, River Trnovcica – LEVKOV et al. 2005, Apennine Mountains – TORRISI and DELL’UOMO 2008, River Raška – VIDAKOVIC et al. 2014; On-line Supplement Fig. 1). Recently N. jakov- ljevicii was reported from the northern region of Europe (The Netherlands, 2010, On-line Supplement Fig. 1). Only few data are available regarding to the substrate of this diatom taxon. Samples containing N. jakovljevicii were collected from limestone (Lake Zug – REICHARDT 1992, Apennine Mountains – TORRISI and DELL’UOMO 2008), branches (River Krka – REICHARDT 1992) and encrusted moss (Plitvice Lakes – REICHARDT 1992). A related species: Navicula lucida We proved the presence of the 'giant form' of Navicula jakovljevicii in Tertiary deposits that was mentioned by LANGE-BERTALOT (2001). This large diatom was described by József Pantocsek as Navicula lucida (PANTOCSEK 1982). All of the main valve features (shape, api- ces, striae pattern, raphe) of these two species are the same, but there are signifi cant differ- ences in valve dimensions. In our observation the valves belonging to N. lucida are large and heavily silicifi ed. This is not surprising, since most diatomite in Central Europe is con- nected to volcanisms (e.g. HAJÓS 1986). High silicate concentration in the lake water, relat- ed to volcanic activity, probably facilitated the development of strong diatom cell walls during the Miocene (WITKOWSKI et al. 2011). All characteristic features are in agreement with N. jakovljevicii and N. lucida, but probably the forked raphe terminals are the most remarkable. We can only speculate about the connection between the extinct and the extant Navicula species. It might be possible that these two species are close relatives. N. lucida could be the ancestor of N. jakovljevicii, the large form gradually diminishing in parallel with the restricted silica supply because of the reduced volcanic activity. But maybe they developed independently from each other. Due to the sporadic occurrences of diatom de- DISTRIBUTION AND COMPARATIVE MORPHOLOGY OF NAVICULA JAKOVLJEVICII ACTA BOT. CROAT. 74 (2), 2015 261 posits, the lack of a continuous profi le makes the answer to this question diffi cult. Navicula lucida was found in Neogene fossil deposits – Köpecz (Căpeni), Bodos (Bodoş) and Bibarczfalva (Baraolt) – in Romania. Furthermore, the presence of this taxon was detected in the Kichevo Basin Macedonia (OGNJANOVA-RUMENOVA and DUMURDZHANOV 2008 as Brachysira sp. on Plate 2 fi g. 6). Perspectives Notwithstanding the intensive studies on the biogeography of diatoms, our knowledge about their distribution pattern is very limited. Detailed taxonomical studies have often re- vealed several new taxa (POTAPOVA and HAMILTON 2007, NOVAIS et al. 2009), but changes in species’ distribution are poorly known. Recently, attention has been paid to invasive and expansive diatom taxa (COSTE and ECTOR 2000, BLANCO and ECTOR 2009, KAŠTOVSKÝ et al. 2010, JELLYMAN et al. 2011, BELTRAMI et al. 2012, T-KRASZNAI et al. 2014), but there are only a few taxa with suffi cient available data. The species mostly in the focus of attention are those that have caused drastic ecological and/or economic events (BLANCO and ECTOR 2009). The incorrect identifi cation of certain taxa (especially closely related-taxa, or centric diatoms) could create diffi culties in the interpretation of the appropriate biogeographical data in some cases (KAŠTOVSKÝ et al. 2010). Navicula jakovljevicii has even been regarded as a rare species (COSTE and ECTOR 2000, VIDAKOVIC et al. 2014). Its occurrence in the Hungarian part of the Danube catchment area might be related to the invasive Elodea nuttallii, which may refer to the changes of the habitat. Affected by the Bős/Gabčikovo dam, water fl ow conditions have changed and wa- ter discharge has decreased in the Danube and its catchment area (RÁTH et al. 2003). These changes in hydrological circumstances primarily led to the spread of adventive and/or inva- sive species, like the waterweeds Elodea canadensis and E. nuttallii (RÁTH et al. 2003). A lot of abiotic and biotic factors control the appearance of non-native species in new habitats (B-BÉRES et al. 2012, PORTER et al. 2013, T-KRASZNAI et al. 2014). We speculated that the new observations of N. jakovljevicii in the Hungarian fl ora were primarily due to the spread of E. nuttallii. These macrophytes could be regarded as the transport substrate of N. jakov- ljevicii. But it is pertinent to emphasize that this ‘transport substrate assumption’ requires a lot of further studies. The improving taxonomical skills of diatomologists and the available fl ora books (e.g. Diatoms of Europe) could also contribute new data of the presence and ecological demands of N. jakovljevicii. Conclusion Appearance of new taxa in diatom-fl ora, especially a rare species with little information about its ecological relevancy, requires a lot of care. Even if the abundance of the given taxa is low, its effects on the local microfl ora are unknown and unpredictable. Our results were the fi rst report about the distribution of Navicula jakovljevicii in Hungary. There are only a few data about its distribution in Europe. In order to predict the effects and the direc- tions of the current expansion of the taxon, every single item of data has a major impor- tance. Our result suggests that N. jakovljevicii might appear in the further Danubian catch- ment area, not only in Hungary but in adjacent countries as well. B-BÉRES V., BÁCSI I., T-KRASZNAI E., KÓKAI Z., BUCZKÓ K. 262 ACTA BOT. CROAT. 74 (2), 2015 Acknowledgements We thank the Hungarian Scientifi c Fund for the fi nancial support (OTKA 83999). Fur- thermore, the authors are thankful for the support of TÁMOP 4.2.4. A/2-11-1-2012-0001 »National Excellence Program – Elaborating and operating an inland student and research- er personal support system«, projects (T-Krasznai E., B-Béres V.). 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