Biodiversity of phytoplankton in Duyen Hai town, Tra Vinh province

189 Vietnam Journal of Marine Science and Technology; Vol. 20, No. 2; 2020: 189–197 DOI: https://doi.org/10.15625/1859-3097/20/2/13490 Biodiversity of phytoplankton in Duyen Hai town, Tra Vinh province Le Thi Trang * , Nguyen Van Tu, Tran Thi Lan Anh, Luong Duc Thien Institute of Tropical Biology, VAST, Vietnam * E-mail: letrangenvi@gmail.com Received: 9 September 2019; Accepted: 19 December 2019 ©2020 Vietnam Academy of Science and Technology (VAST) Abstract This study was conducted to enhance the understanding of phytoplankton diversity of Duyen Hai town, Tra Vinh province. We selected 12 representative sampling sites and investigated phytoplankton diversity in both dry and rainy seasons. The phytoplankton of this area were comprised of 134 species, belonging to 64 genera, 45 families, 31 orders, 8 classes and 5 divisions. Among those divisions, Bacillariophyta was the most dominant in species, accounting for 70% of the total number of species and Cyanobacteria commonly had high density at 12 surveyed sites. The average density of phytoplankton was 1,195 cells/ l in the rainy season and 2,020 cells/l in the dry season, respectively. For water bodies with the exchange of freshwater and marine water, the diversity is typically higher than in water bodies with purely freshwater or marine conditions. Keywords: Aquatic ecology, biodiversity, diatoms, phytoplankton, Tra Vinh. Citation: Le Thi Trang, Nguyen Van Tu, Tran Thi Lan Anh, Luong Duc Thien, 2020. Biodiversity of phytoplankton in Duyen Hai town, Tra Vinh province. Vietnam Journal of Marine Science and Technology, 20(2), 189–197. Le Thi Trang et al. 190 INTRODUCTION Duyen Hai town is located in the southeast of Tra Vinh province. It is bounded in the east and the south by the East Sea, in the west by Duyen Hai district, and in the north by Cau Ngang district. Duyen Hai aquatic system is influenced by the semi-diurnal tide (two high and two low tides each day), with the regime of high tidal amplitude and strong current. The systems of Thau Rau, Ba Dong, Long Toan rivers, and Tat channel control the entire network of rivers and distribute water throughout the town. In addition, there is a network of rivers, canals, and irrigation channels that distribute water sources to inland and aquaculture development areas. Due to the characteristics of the region with dense river systems, the water resources of Duyen Hai town are plentiful and diverse. It is a favorable condition for the presence, living and diversification of aquatic species in the region. The appearance of phytoplankton is typically closely related to the ecological and environmental conditions, these species are production organisms in some food webs, capable of expediting material transition in the aquatic system and may be an indicator for water quality [1–4]. The studies of coastal phytoplankton for Vietnam started in 1926 since Maurice Rose reported 20 species of diatoms for the Nha Trang bay [5]. In 1966, Shirota described 213 species of diatoms along coastline from Thuan An (Thua Thien-Hue province) to Phu Quoc (Kien Giang province) [5]. In 1993, Truong Ngoc An described 244 species in the book “Taxonomy of Bacillariophyta plankton in marine water of Vietnam” [5]. Recently, some of the researches on coastal phytoplankton at local scale have contributed to the understanding of diversity of phytoplankton in Vietnam. At the Central coast Pham Thi My Hanh (2013) reported 144 species [6], at the West-Sea zone of Ca Mau peninsular Luong Van Thanh (2008) reported 216 species [7], and in the coastal areas from Soc Trang to Bac Lieu Mai Viet Van et al., (2012) reported 232 species [8]. Among these studies, diatom was the most abundant group of the species list. So far, the studies on the diversity of phytoplankton in the coastal area of Tra Vinh province have not been carried out yet. This research aims to explore phytoplankton diversity in Duyen Hai town for further works on the conservation, rational use, and sustainable development. MATERIALS AND METHODS Study area This study selected 12 locations representative of the whole coastal zone and inland area of the Duyen Hai town, Tra Vinh province. Phytoplankton samples were collected during the rainy (July) and dry (December) seasons in 2017. The sampling sites are shown in figure 1 below. Sample collection Phytoplankton samples were taken by the method of Edward and David (2010) [9]. Qualitative samples of phytoplankton were collected from the surface waters by towing a plankton net (with a mesh size of 25 µm, mouth diameter of 40 cm, repeating 3–5 times/sample, and speed at 0.3 m/s). Quantitative samples of phytoplankton were collected by filtering 40 liters of water through the plankton net. The collected samples were stored in plastic jars with a volume of 250 ml and fixed with 5% formalin at the field. Data analysis Olympus BX51 optical microscope at 100- 400X magnification was used to identify phytoplankton according to the morphological method based on the classification books such as Desikachary (1959) [10]; Hendey (1964) [11]; Shirota (1966) [12]; Truong Ngoc An (1993) [5]; Duong Duc Tien and Vo Hanh (1997) [13]; Ton That Phap (2009) [14]. Quantitative samples were allowed to settle for 24 hours in the laboratory and then concentrated to 20 ml/sample. Phytoplankton density was counted in 1 ml in the Sedgewick-Rafter counting chamber by the method of Edward and David (2010) [9] and then converted to the number of cells in 1 liter. The phytoplankton taxa are searched and sorted according to AlgaeBase’s taxonomy system [15]. The samples of phytoplankton were analyzed at the laboratory of the Institute of Tropical Biology. Biodiversity of phytoplankton in Duyen Hai town 191 Figure 1. The map of sampling sites in Duyen Hai town, Tra Vinh province RESULTS Phytoplankton community structure 134 species of phytoplankton flora of Duyen Hai town, Tra Vinh province were recorded, which belong to 64 genera, 45 families, 31 orders, 8 classes, and 5 divisions, namely Cyanophyta, Bacillariophyta, Chlorophyta, Euglenophyta, and Dinophyta. Among those divisions, Bacillariophyta had the most diverse species composition with 98 species, occupying 73.1%; followed by Cyanophyta with 21 species, occupying 15.7%; Dinophyta with 8 species, occupying 6.0% and Chlorophyta with 5 species, occupying 3.7%; and the lowest species composition belonged to Euglenophyta with 2 species, occupying 1.5% (table 1, figure 2). This phytoplankton flora is comprised of many species which are typical of the phytoplankton communities of the coastal Le Thi Trang et al. 192 and estuarine regions. The Biddulphia, Coscinodiscus, Chaetoceros, Ditylum, Gyrosigma, Nitzschia, Pleurosigma, Rhizosolenia, and Skeletonema are representative genera in these groups. However, some of the species from freshwater were recorded as well, such as Anabaena, Microcystis, Oscillatoria, Pediastrum simplex, Scenedesmus quadricauda, Oedogonium sp., and Spirogyra ionia (table 2). This proves that the aquatic environment in the study area was mainly co- affected by seawater via the tide and a part of freshwater from inland region. Table 1. Structure of phytoplankton species composition in Duyen Hai town, Tra Vinh province No. Phylum Class Order Family Genus Species Ratio % 1 Cyanophyta 1 3 5 11 21 15,7 2 Bacillariophyta 3 20 30 42 98 73,1 3 Chlorophyta 2 4 5 5 5 3,7 4 Euglenophyta 1 1 1 2 2 1,5 5 Dinophyta 1 3 4 4 8 6,0 Total 8 31 45 64 134 100 Figure 2. Composition structure of phytoplankton Table 2. List of phytoplankton species from Duyen Hai town, Tra Vinh province Taxon Taxon Phylum Cyanophyta 74. Asteromphalus flabellatus (Brébisson) Greville, 1859 Class Cyanophyceae Order Thalassiosirales Order Chroococcales Family Skeletonemataceae Family Microcystaceae 75. Skeletonema costatum (Greville) Cleve, 1873 1. Microcystis aeruginosa (Kützing) Kützing, 1846 Family Stephanodiscaceae 2. Microcystis panniformis Komárek, Komárková- Legnerová, Sant’Anna, M. T. P. Azevedo, & P. A. C. Senna, 2002 76. Cyclotella comta (Ehrenberg) Kützing, 1849 Order Oscillatoriales 77. Cyclotella meneghiniana Kützing, 1844 Family Pseudanabaenaceae Họ Lauderiaceae 3. Jaaginema sp. 78. Lauderia borealis Gran, 1900 Family Phormidiaceae Order Biddulphiales 4. Arthrospira sp. Family Biddulphiaceae 5. Phormidium tenue Gomont, 1892 79. Biddulphia aurita (Lyngbye) Brébisson, 1838 6. Planktothrix agardhii Anagnostidis & Komárek, 1988 80. Biddulphia mobiliensis (J. W. Bailey) Grunow, 1882 Family Oscillatoriaceae 81. Biddulphia regia (Schultze) Ostenfeld, 1908 7. Lyngbya majuscula Harvey ex Gomont, 1892 82. Biddulphia sinensis Greville, 1866 8. Lyngbya martensiana Menegh. ex Gomont, 1892 83. Hydrosera triquetra G. C. Wallich 9. Lyngbya sp. Order Triceratiales 10. Oscillatoria acuta Bruhl et Biswas, 1932 Family Triceratiaceae 11. Oscillatoria curviceps C. Agardh ex Gomont, 1892 84. Triceratium favus Ehrenberg, 1839 Biodiversity of phytoplankton in Duyen Hai town 193 12. Oscillatoria limosa C. Agardh ex Gomont, 1892 Order Hemiaulales 13. Oscillatoria princeps Vaucher ex Gamont, 1892 Family Hemiaulaceae 14. Oscillatoria perornata Skuja, 1949 85. Hemiaulus membranaceus Cleve, 1873 15. Oscillatoria proboscidea Gomont, 1892 86. Hemiaulus sinensis Greville, 1865 16. Oscillatoria tenuis Agardh, 1813 87. Cerataulina pelagica (Cleve) Hendey, 1937 17. Oscillatoria sp. 88. Climacodium biconcavum Cleve, 1897 18. Trichodesmium erythraeum Ehrenberg ex Gomont, 1892 Family Bellerocheaceae Order Nostocales 89. Bellerochea horologicalis Stosch, 1980 Family Nostocaceae 90. Bellerochea indica Karsten, 1907 19. Anabaena sp. Family Streptothecaceae 20. Anabaenopsis circularis Woloszynska & V. Miller, 1923 91. Streptotheca thamesis Shrubsole, 1891 21. Aphanizomenon aphanizomenoides (Forti) Horecká et Komárek, 1979 Family Lithodesmiales Phylum Bacillariophyta Family Lithodesmiaceae Class Bacillariophyceae 92. Ditylum brightwellii (T.West) Grunow, 1885 Order Achnanthales 93. Ditylum sol (Grunow) De Toni, 1894 Family Achnanthaceae Order Chaetocerotales 22. Achnanthes brevipes C.Agardh, 1824 Family Chaetocerotaceae Family Cocconeidaceae 94. Bacteriastrum hyalinum Lauder, 1864 23. Cococines sp. 95. Chaetoceros aequatorialis Cleve, 1901 Order Thalassiophysales 96. Chaetoceros affinis Lauder, 1864 Family Catenulaceae 97. Chaetoceros curvisetus Cleve, 1889 24. Amphora sp. 98. Chaetoceros decipiens Cleve, 1873 Order Naviculales 99. Chaetoceros indicus Karsten, 1907 Family Naviculaceae 100. Chaetoceros lauderi Ralfs ex Lauder, 1864 25. Navicula membranacea Cleve, 1897 101. Chaetoceros lorenzianus Grunow, 1863 26. Navicula sp. 102. Chaetoceros subtilis Cleve, 1896 27. Trachyneis aspera (Ehrenberg) Cleve, 1894 Order Rhizosoleniales 28. Trachyneis debyi (Leuduger-Fortmorel) Cleve,1894 Family Rhizosoleniaceae Family Pinnulariaceae 103. Guinardia flaccida (Castracane) H. Peragallo, 1892 29. Pinnularia major (Kützing) Rabenhorst, 1853 104. Dactyliosolen mediterraneus H. Peragallo, 1892 Family Pleurosigmataceae 105. Rhizosolenia alata f. genuina Gran, 1908 30. Gyrosigma acuminatum (Kützing) Rabenhorst, 1853 106. Rhizosolenia alata f. indica (H. Peragallo) Gran, 1905 31. Gyrosigma attenuatum (Kützing) Rabenhorst, 1853 107. Rhizosolenia bergonii H. Peragallo, 1892 32. Gyrosigma balticum (Ehrenberg) Rabenhorst, 1853 108. Rhizosolenia calcar- avis Schultze, 1858 33. Gyrosigma scalproides (Rabenhorst) Cleve 1894 109. Rhizosolenia crassispina J. L. B. Schröder, 1906 34. Gyrosigma sp. 110. Rhizosolenia imbricata Brightwell, 1858 35. Gyrosigma sinense (Ehrenberg) Desikachary, 1988 111. Rhizosolenia imbricata var. shrubsolei Schröder, 1906 36. Gyrosigma wormleyi (Sullivant) Boyer, 1922 112. Rhizosolenia robusta G. Norman ex Ralfs, 1861 37. Pleurosigma angulatum (Queckett) W. Smith, 1852 113. Rhizosolenia setigera Brightwell, 1858 38. Pleurosigma elongatum W. Smith, 1852 114. Rhizosolenia styliformis T. Brightwell, 1858 39. Pleurosigma naviculaceum Brébisson, 1854 Class Fragilariophyceae 40. Pleurosigma strigosum W. Smith, 1852 Order Climacospheniales Order Bacillariales Family Climacospheniaceae Family Bacillariaceae 115. Climacosphenia moniligera Ehrenberg, 1843 41. Cylindrotheca closterium Reimann & J. C. Lewin, 1964 Order Thalassionematales 42. Nitzschia closterium (Ehrenberg) W. Smith, 1853 Family Thalassionemataceae 43. Nitzschia lorenziana Grunow, 1880 116. Lioloma pacificum (Cupp) Hasle, 1996 44. Nitzschia paradoxa (J. F. Gmelin) Grunow, 1880 117. Thalassionema nitzschioides Mereschkowsky, 1902 45. Nitzschia palea (Kützing) W.Smith, 1856 118. Thalassionema frauenfeldii Hallegraeff, 1986 46. Nitzschia plana W.Smith, 1853 Order Fragilariales 47. Nitzschia sigma (Kützing) W. Smith, 1853 Family Fragilariaceae 48. Pseudo-nitzschia seriata (Cleve) H. Peragallo, 1899 119. Synedra ulna (Nitzsch) Ehrenberg, 1832 Family Surirellaceae Phylum Chlorophyta 49. Campylodiscus daemelianus Grunow, 1874 Class Chlorophyceae 50. Campylodiscus echeneis Ehrenberg ex Kützing, 1844 Order Chlorococcales Le Thi Trang et al. 194 51. Surirella fastuosa (Ehrenberg) Ehrenberg, 1843 Family Hydrodictyaceae 52. Surirella gemma Ehrenberg, 1839 120. Pediastrum simplex Meyen, 1829 53. Surirella ovata Kützing, 1844 Family Scenedesmaceae 54. Surirella ovalis Brébisson, 1838 121. Scenedesmus quadricauda (Turpin) Brébisson, 1835 55. Surirella robusta Ehrenberg, 1840 Order Oedogoniales Order Cymbellales Family Oedogoniaceae Family Cymbellaceae 122. Oedogonium sp. 56. Cymbella lanceolata (C. Agardh) Kirchner, 1878 Order Volvocales 57. Cymbella tumida (Brébisson) van Heurck, 1880 Family Volvocaceae Order Plagiogrammales 123. Volvox aureus Ehrenberg, 1832 Family Plagiogrammaceae Class Zygnematophyceae 58. Plagiogramma vanheurckii Grunow, 1881 Order Zygnematales Class Coscinodiscophyceae Family Zygnemataceae Order Coscinodiscales 124. Spirogyra ionia Wade, 1949 Family Coscinodiscaceae Phylum Euglenophyta 59. Coscinodiscus asteromphalus Ehrenberg, 1844 Class Euglenophyceae 60. Coscinodiscus concinnus W.Smith, 1856 Order Euglenales 61. Coscinodiscus gigas Ehrenberg, 1841 Family Euglenaceae 62. Coscinodiscus jonesianus (Greville) Ostenfeld, 1915 125. Euglena acus Ehrenberg, 1830 63. Coscinodiscus bipartitus Rattray, 1890 126. Trachelomonas hispida (Perty) F.Stein,1878 64. Coscinodiscus radiatus Ehrenberg, 1841 Phylum Dinophyta 65. Coscinodiscus rothii (Ehrenberg) Grunow, 1878 Class Dinophyceae 66. Coscinodiscus subtilis Ehrenberg, 1841 Order Gonyaulacales 67. Coscinodiscus sp. Family Ceratiaceae Family Heliopeltaceae 127. Ceratium furca Claparède & Lachmann, 1859 68. Actinoptychus undulatus (Kützing) Ralfs, 1861 128. Ceratium fusus (Ehrenberg) Dujardin, 1841 Family Hemiaulaceae 129. Ceratium macroceros (Ehrenberg) Vanhöffen, 1897 69. Hemidiscus hardmannianus (Greville) Kuntze, 1898 130. Ceratium vultur Cleve, 1900 Order Melosirales Order Peridiniales Family Melosiraceae Family Kolkwitziellaceae 70. Melosira granulata (Ehrenberg) Ralfs,1861 131. Diplopsalis lenticula Bergh, 1882 71. Melosira moniliformis (O. F. Müller) C. Agardh, 1824 Family Protoperidiniaceae 72. Melosira nummuloides C.Agardh, 1824 132. Protoperidinium divergens (Ehrenberg) Balech, 1974 Order Paraliales 133. Protoperidinium subinerme (Paulsen) Loeblich III, 1969 Family Paraliaceae Order Thoracosphaerales 73. Paralia sulcata (Ehrenberg) Cleve, 1873 Family Thoracosphaeraceae Family Asterolampraceae 134. Goniodoma sphaericum Murray & Whitting, 1899 Phytoplankton densities and dominant species The density and dominant species of phytoplankton in Duyen Hai town have shown a difference between seasons and locations. In the rainy season, the density of phytoplankton between locations had a significant difference, ranging from 129 to 3,830 cells/l, with the maximum at the station DH08 and the minimum at the station DH11. The filamentous blue-green algae such as Oscillatoria perornata, O. princeps, O. proboscidea, and Lyngbya sp. grew well. These species dominated at ten of twelve sampling sites, at each station these species occupied from 35.3% to 77.2% of the total cells. Particularly, at two sampling sites of DH10 and DH11, diatom species like Coscinodiscus jonesianus and Melosira granulata were dominant, occupying 24.8% and 54.3% of the total cells, respectively (table 3). In the dry season, phytoplankton density was somewhat higher than in the rainy season, the cell number of phytoplankton ranged from 66–10,636 cells/l, with the highest at the station DH03 and the lowest at the station DH07. The dominant species in dry season were Oscillatoria princeps, Lyngbya majuscula, Lyngbya sp. belonging to blue-green algae which occupied from 19.4% to 93.9% of the total cells, except for two sampling sites of DH07 and DH09, the diatom Skeletonema costatum dominated, occupying 45.5% and 52.9% of the total cells, respectively (table 3). Biodiversity of phytoplankton in Duyen Hai town 195 Table 3. Density and dominant species of phytoplankton from Duyen Hai town, Tra Vinh province Sampling sites Dominant species Total density (cells/l) Density of dominant species (cells/l) Ratio of dominant species (%) Rainy season DH01 Oscillatoria perornata 2,225 814 36.6 DH02 Oscillatoria princeps 1,932 1,000 51.8 DH03 Lyngbya sp. 756 200 26.5 DH04 Oscillatoria proboscidea 486 375 77.2 DH05 Lyngbya sp. 2,590 1,214 46.9 DH06 Lyngbya sp. 279 200 71.7 DH07 Lyngbya sp. 177 86 48.6 DH08 Oscillatoria perornata 3,830 1,351 35.3 DH09 Oscillatoria princeps 342 150 43.9 DH10 Coscinodiscus jonesianus 137 34 24.8 DH11 Melosira granulata 129 70 54.3 DH12 Oscillatoria princeps 1,452 520 35.8 Dry season DH01 Lyngbya majuscula 693 200 28.9 DH02 Oscillatoria princeps 145 70 48.3 DH03 Oscillatoria princeps 10,636 5,720 53.8 DH04 Lyngbya majuscula 2,058 400 19.4 DH05 Oscillatoria princeps 4,873 1,764 36.2 DH06 Lyngbya sp. 391 367 93.9 DH07 Skeletonema costatum 66 30 45.5 DH08 Oscillatoria princeps 1,284 420 32.7 DH09 Skeletonema costatum 820 434 52.9 DH10 Oscillatoria princeps 204 166 81.4 DH11 Oscillatoria princeps 2,719 1,280 47.1 DH12 Oscillatoria princeps 353 220 62.3 DISCUSSION In Vietnam, several studies on phytoplankton in some areas, which have environmental characteristic similarity to Duyen Hai, Tra Vinh province, have been conducted so far. In 2008, Luong Van Thanh [7] reported 16 species of phytoplankton belonging to seven algal divisions (Cyanophyta, Chrysophyta, Xanthophyta, Bacillariophyta, Chlorophyta, Euglenophyta, Dinophyta) in the estuaries of West-Sea zone of Ca Mau peninsula; in this research, Bacillariophyta was dominant with 53.7% of the total number of species. With similar environment condition in the coastal areas from Soc Trang to Bac Lieu province, the research of Mai Viet Van et al., (2012) [8] reported 232 algal species belonging to only four divisions (Bacillariophyta, Dinophyta, Cyanophyta, and Chlorophyta), however, Bacillariphyta randomly occupied 74.57% of the total number of species. In the other study, Pham Thi Minh Hanh (2013) [6] recorded 144 species belonging to three divisions (Bacillariophyta, Dinophyta, and Cyanophyta), and confirmed that the Bacillariophyta was the dominant group in species number at the Central coastal region of Vietnam (Deo Ngang, Dong Hoi, Con Co, Thuan An, Da Nang, Dung Quat, Sa Huynh, Quy Nhon). The result of Huynh Thi Ngoc Duyen et al., (2018) [16] shown 238 species belonging to four divisions (Bacillariophyta, Dinophyta, Ochrophyta, and Cyanophyta) in the coastal waters of Ninh Thuan - Binh Thuan and Bacillariophyta played the main role in the structure of species composition. In comparison to the above researches, the phytoplankton flora of Duyen Hai town does not reflect diversity in species but show higher diversity in the division. Similar to other research, this research again confirms that Bacillariophyta plays the leading role in the structure of phytoplankton composition at the estuary and coastal waters. The diversity of phytoplankton in the coastal area of Duyen Hai town has been Le Thi Trang et al. 196 clearly shown at the diatom group. Among 98 species of diatom recorded for this area, many of them have been reported in a single genus. The number of species in the diatom genera was ordered as follows: Rhizosolenia (10 species) > Coscinodiscus (9 species) > Chaetoceros (8 species) > Gyrosigma (7 species) > Nitzschia (6 species) > Surirella (5 species) > Biddulphia, Pleurosigma (4 species). Only Oscillatoria genus of the blue-green algae group was recorded with eight species and only Ceratium genus of dinoflagellate group was recorded with four species. The other genera appeared with only 1 or 2 species. Phytoplankton are the primary producer in the aquatic food chain and play a significant role in the aquatic ecosystem. The density of phytoplankton in both rainy and dry seasons in Duyen Hai town ranged from 1,000 to 2,000 cells/l, this density is settled at medium level but contributes an important role in connecting the food web in this area. CONCLUSION 134 species of phytoplankton flora in the coastal region of Duyen Hai town, Tra Vinh province were recorded, belonging to 64 genera, 45 families, 31 orders, 8 classes, and 8 divisions. The number of species in the flora list was arranged as follows: Bacillariophyta > Cyanophyta > Dinophyta > Chlorophyta > Euglenophyta. The species composition of phytoplankton was characteristic of the estuarine and coastal areas, however, there were some freshwater species that were widely environmentally distributed. These phytoplankton species are a primary food source for aquatic organisms. Bacillariophyta was dominant in the number of species and Cyanophyta was dominant in cell density. 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