(Planchon) St. John – a competitive hydrophyte in the Romanian Danube river corridors

Anca Sârbu1, Daniela Smarandache1, Georg Janauer2 and Gabriela Pascale1

Introduction The longest reach of the Danube River borders, or crosses the Romanian territory, respectively. The composition and distribution of aquatic vegetation is specific for the diversity of the channel types in the Danube River corridor. Increased eutrophication stimulates the development of some well-adapted cormophytes (Sârbu 2006). Therefore, special attention was given to the two Elodea species found in the Romanian flora: Michx., a long-established hydrophyte (Poplavskaia 1948) and Elodea nuttallii (Planchon) St. John, an adventive species (Ciocârlan et al. 1998), which is very competitive in eutrophic conditions.

Methods This study was carried out in Romania, between 2002-2004 in all the Romanian Danube river corridors: main channel (1346 km), river branches (951 km) and in ten Danube Delta channels (186 km). It was part of the international project “Macrophyte Inventory Danube – Corridor and Catchment” (www.midcc.at) funded by the Austrian Federal Ministry of Education, Science and Culture. The field assessment of aquatic macrophytes was based on the methodology developed by Kohler (Kohler et al. 1971, Kohler 1978, Kohler and Janauer 1995; contiguous survey units, 5-level estimator scale: 1 – rare, 2 – occasional, 3 – frequent, 4 – abundant, 5 – very abundant), in accordance with the European Standard EN 14184 (2003), which is also relevant for the EU Water Framework Directive. Diversity and abundance of aquatic species is displayed in diagrams: Distribution Diagrams, Relative Plant Mass (RPM) and Average Distribution of species (MMT/O/d). Structural analyses of the stem and assimilatory pigments assessment were carried out also. In stem cross section analysis Congo red & cryzoidine were used to staining the cellulose (in red color). Assimilatory pigments were analyzed spectrophotometrically (chlorophyll a λ = 662 nm, chlorophyll b λ = 644 nm, carotenoide pigments λ = 440 nm).

Results Elodea nuttallii was recorded in the Danube River main channel, except river km 252-177 (left-side), in the 5 river branches (Borcea, Măcin, Chilia, Sulina, Sf. Gheorghe) and in 50% of the assessed smaller channels in the delta. E. canadensis was found only in one oxbow located along the Danube river main channel, between river km 930-794. Regarding the metrics Relative Plant Mass and Average Distribution, E. nuttallii was assessed as “frequent” in the narrow channels in the Danube Delta (Fig. 1, Fig. 2) and in the river branches (Fig. 3, Fig. 4) and as “occasional” in the Danube river main channel (Fig. 5, Fig. 6). The mean value of the total assimilatory pigments was 14.75 mg g-1 dry weight, with a range of the mean values of 9.0-19.40 mg g-1 dry weight. This values are higher than to those recorded for E. canadensis (12.42 mg g-1 dry weight; ranges of the mean values of 9.10-14.80 mg g-1 dry weight) and closer to those of Ceratophyllum demersum (Sârbu et al. 1999). E. nuttallii has a thicker, more compact and stronger stem than E. canadensis (Fig. 7, Fig. 8). The aerenchyma

1 University of Bucharest, Department of Botany, Aleea Portocalelor 1-3, Sector 5, 060101 Bucureşti, Romania 2 Department für Limnologie und Hydrobotanik, Universität Wien, Althanstrasse 14, A – 1090 Wien, Austria

107 consists almost of one row of canals (Fig. 8). The cortex cells, the parenchyma cells from the central cylinder and also the epidermis cells develop thick cellulose walls, which provide a support for the stem, without restraining growth (Fig. 9, Fig. 10).

Danube Author:Sarbu Anca Danube Delta channels v3.5, www.biogis.net Document ID:5_05_1_9_10_87, Survey Code:40_13_20 (c) 2001-2003, Exler Alg fil Azo fil But umb Cer dem Cer sub Cha sp. Elo nut Hip vul Hot pal Hyd mor Lem gib Lem min Lem tri Myr spi Naj mar Nit sp Nup lut Nym alb Nym pel Oen aqu Pol amp Pot acu Pot cri Pot luc Pot nat Pot nod Pot pec Pot per Pot pus Sag sag Sag tri Sal nat Sch lac Spa eme Spa ere Spi pol Str alo Tra nat Val spi 1 2 3 4 5 0 0.5 1 Figure 1. Average distribution of species (MMT/O/d) – Danube Delta channels

Danube Author:Sarbu Anca Danube Delta channels v3.5, www.biogis.net Document ID:5_05_21_12_37_58, Survey Code:40_13_20 (c) 2001-2003, Exler Cer dem Sal nat Tra nat Lem min Spi pol Elo nut Nup lut But umb Sag sag Hyd mor Pot nod Pot pec Str alo Nym alb residual (25) 0 10 20 % Figure 2. Relative Plant Mass (RPM) – Danube Delta channels

108 Test Data for Top-Down Author:Anca Sarbu Danube Author:"Sarbu Smarandache Mitache Pascale Litescu Oprea" Danube v3.5, www.biogis.net Bazias-Tulcea v3.5, www.biogis.net Document ID:5_05_3_7_16_75, Survey Code:40_13_1 (c) 2001-2003, Exler Document ID:6_06_20_13_56_98, Survey Code:40_13_1 (c) 2001-2003, Exler Alg fil Alg fil Azo fil But umb But umb Cer dem Cer dem Cer sub Cer sub Cla glo Elo can Elo nut Elo nut Hip vul Hot pal Hyd mor Hyd mor Lem min Lem gib Lem tri Lem min Myr spi Lem tri Myr ver Myr spi Naj mar Myr ver Nup lut Naj mar Naj min Nym alb Nym alb Nym pel Nym pel Oen aqu Oen aqu Pol amp Pol amp Pot cri Pot acu Pot flu Pot cri Pot luc Pot gra Pot gra Pot luc Pot nat Pot nat Pot nod Pot nod Pot pec Pot pec Pot per Pot per Pot pus Pot pus Pot tri Pot tri Sag sag Sag sag Sag tri Sag tri Sal nat Sal nat Sch lac Sch lac Spa ere Spa ere Spi pol Spi pol Tra nat Str alo Val spi Tra nat Ver ana Val spi Wol arr Ver ana Zan pal 1 2 3 4 5 0 0.5 1 1 2 3 4 5 0 0.5 1

Figure 3. Average distribution of species (MMT/O/d) – Danube river branches Figure 5. Average distribution of species (MMT/O/d) – Danube river main channel

Test Data for Top-Down Author:Anca Sarbu Danube v3.5, www.biogis.net Danube Author:"Sarbu Smarandache Mitache Pascale Litescu Oprea" Document ID:6_06_20_13_56_98, Survey Code:40_13_1 (c) 2001-2003, Exler Bazias-Tulcea v3.5, www.biogis.net Document ID:5_05_3_7_16_75, Survey Code:40_13_1 (c) 2001-2003, Exler But umb Cer dem Cer dem Pot per Alg fil Spi pol Pot nod But umb Sal nat Cer sub Pot pec Pot nat Tra nat Pot pec Pot per Pot luc Spi pol Myr spi Pot nat Lem min Cla glo Pot cri Val spi Tra nat Sch lac Pot nod Pot tri Wol arr Pot gra Elo can Lem min Elo nut residual (21) residual (24) 0 10 % 0 10 % Figure 4. Relative Plant Mass (RPM) – Danube river branches Figure 6. Relative Plant Mass (RPM) – Danube river main channel

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Figure 7. E. canadensis – stem, cross section Figure 8. E. nuttallii – stem, cross section (Poplavskaia 1948) (Oc 12,5x; Ob 10; Amp. 12,5)

Figure 9. E. nuttallii – stem, cross section, Figure 10. E. nuttallii – stem, cross section, detail of the cortex and central detail of the cortical cells cylinder (Oc 12,5x; Ob 10; Amp. 16) (Oc 12,5x; Ob 10; Amp. 25)

110 Disscusion First nominated for the Danube Delta in 1998, Elodea nuttallii was found between 2002-2004 in the majority of the Romanian Danube river corridors: in 90% of the main channel, 100% of the river branches and 50% of the assessed delta channels, but it was nowhere dominant. In the delta channels this species, evaluated as “frequent”, realized the most significant RPM value (7%), but placed under the dominance values. In the Danube river arms it was “frequent” and in the river main channel it was “occasional”, but the RPM values were very low (‘residual’). This position can be related to its short period of presence in the Romanian Danube River reach. Anyhow, the existing information (Sârbu 1999) associated with the results of the present study confirm the replacement of E. canadensis with E. nuttallii in the last 5 years, at least in two channels (Old Danube and Magearu) from the Danube Delta. Some physiological and structural characteristics support the hypothesis on the rapid increase in the E. nuttallii population: (i) higher content of assimilatory pigments, which ensure its significant success in the competition for light, (ii) the presence of a stem strengthened by the features of its cell walls, which allows for efficient vertical growth, (iii) the capacity to form a high number of “winterbuds” from which young will start to develop in spring. It is therefore of no surprise that it could effectively out-compete E. canadensis.

Summary E. nuttallii, a short-time adventive species in Romania, became a non-negligible element of the communities of Romania. Its physiological and structural features offer a significant advantage in the interspecific competition.

References CIOCARLAN, V., SARBU, I., STEFAN, N. & T. MARIAN (1998): Elodea nuttallii (Planchon) St. John a new specie in Romanian flora. – Bul. Bot. Garden. 6(1): 215-231. KOHLER, A., VOLRATH, H., BEISL., E. (1971): Zur Verbreitung, Vergesellschaftung und Ökologie der Gefäßmakrophyten im Fließwassersystem Moosach (Műnchner Ebene). – Arch. Hydrobiol. 69(3): 333-365. KOHLER, A. (1978): Methoden der Kartierung von Flora und Vegetation von Süßwasserbiotopen. Landschaft und Stadt, 10: 73-85. KOHLER, A. & JANAUER, G. (1995): Zur Methodik der Untersuchung von aquaitschen Makrophyten in Fließgewässern. In: Steinberg, Ch., Bernhard, H., Klapper, H. (eds.) Handbuch der angewandten Limnologie VIII-1.1.3, 1,22. Ecomed, Landsberg/Lech. SARBU, A. (2003): Inventory of aquatic plants in the Danube Delta, a pilot study in Romania. – Arch. Hydrobiol. Suppl. 147/1-2: 205-216 SARBU, A. (2006): Aquatic macrophytes. – In: Tudorancea, C. and Tudorancea, M. (ed.): Danube Delta Genesis and Biodiversity: 133-175. Backhuys Publichers, Leiden, The Netherlands. SARBU, A., CRISTOFOR, S., VADINEANU, A., FLORESCU, C., SMARANDACHE D. (1999): Dynamics of photosynthetic pigments content of the main submerged macrophytes in the Danube Delta. – An. St. Inst. Delta Dunării. 3: 279-289. POPLAVSKAIA, I.G. (1948): Ekologiia Rastenij. pp 294. Sovetskaia nauka, Moskva.

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