Spatial and temporal variations in phytoplankton abundance and species diversity in the Sundarbans mangrove forest of Bangladesh

Rahaman et al., J Marine Sci Res Dev 2013, 3:2 http://dx.doi.org/10.4172/2155-9910.1000126 Marine Science Research & Development Research Article Research Article OpenAccess Access Open Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh Rahaman SMB1*, Golder J2, Rahaman MS3, Hasanuzzaman AFM1, Huq KA1, Begum S2, Islam SS1 and Bir J1 1 2 3 Fisheries and Marine Research Technology Discipline, Khulna University, Khulna 9208, Bangladesh Environmental Science Discipline, Khulna University, Khulna 9208, Bangladesh Department of Chemistry, Comilla University, Comilla 3500, Bangladesh Abstract The study examined taxonomic composition, abundance and spatial distribution of phytoplankton, and water quality of three major river systems of the Sundarbans. A total of 134 phytoplankton species were identiied, and diversity and abundance were found to luctuate with time and space. A total of 97 species were enumerated in Rupsha-Pashur while 122 and 110 in Khalpatua-Arpangachia and Bhola-Baleswar river system respectively. Abundance was lowest (3.709×103 ± 4.257×102 cellsL-1) in monsoon and highest (2.174×105 ± 1.723×105cellsL-1) in summer in Bhola-Baleswar. Species composition was dominated by Bacillariophyta over the area except in summer in Bhola-Baleswar, where Cyanophyta become dominated. Species diversity, richness and evenness index varied between 2.03-4.64, 1.2-2.44, 0.77-1.5 in Rupsha-Pashur; 2.47-3.85, 1.8-5.84, 0.78-0.94 in Khalpatua-Arpangachia; and 0.66-4.27, 1.19-5.12, 0.59-1.29 in Bhola-Baleswar. Water temperature, pH, DO, Transparency and Salinity were determined between 19.92°C-31°C; 6.7-7.87; 3.93 mgL-1-7.37 mgL-1; 7.5 cm-60 cm; 2-23 ppt, respectively. Nutrient elements i.e. NO3-, PO43-, NH4+, SiO44- luctuated seasonally from 0.0062 to 1.633 mgL-1, 0.005 to 0.772 mgL-1, 0.038 to 2.467 mgL-1, 3.124 to 27.234 mgL-1, respectively. Chlorophyll-a concentrations were luctuated seasonally within 0.24 to 5.94 µgL-1 and highest phytoplankton biomass was observed in Bhola-Baleswar in summer. Chlorophyll concentration was found to be correlated positively with transparency, salinity and nutrients. Keywords: Water quality; Phytoplankton; Biomass production; Monsoon; River system; Estuary; Sundarbans Introduction he Sundarbans; the largest single chunk of tidal halophytic mangrove forest in the world; lies in the vast delta on the Bay of Bengal formed by the greater conluence of the Ganges; Brahmaputra and Meghna rivers. It covers 10,000 sq.km of which about 6000 sq.km area is within the political boundary of Bangladesh; and the remaining in India. he area experiences a subtropical monsoonal climate with an annual rainfall of 1600-1800 mm and severe cyclonic storms. Enormous amounts of sediments carried by the rivers contribute to its expansion and dynamics. he Hydro-geochemical environment of this area is highly dynamic in nature with numerous drainage channels and signiicant coastal processes [1]. he biodiversity includes about 350 species of vascular plants; 250 ishes and 300 birds; besides numerous species of phytoplankton; fungi; bacteria; zooplankton; benthic invertebrates; molluscs; reptiles; amphibians and mammals. Species composition and community structure vary east to west; and along the hydrological and salinity gradients. he Sundarbans with diverse gene pool for lora and fauna provides livelihoods for about 2.5 million people of Bangladesh [2]. Being in the coastal waters; the abiotic and biotic resources of the Sundarbans are highly variable in response to the coastal dynamic processes. he regulation of river lows by a series of dams; barrages and embankments for diverting water upstream for various human needs and for lood control has caused large reduction in freshwater inlow and seriously afected the biodiversity because of an increase in salinity and changes in sedimentation. Ecological characteristics; particularly intermixing of saline and fresh water; seasonally luctuating salinity and the silt brought down by the rivers greatly inluence the distribution and abundance of algae in the Sundarbans. he observed distribution of a given species is a function of diferential adaptations (diferences in reproduction and growth) in response to environmental factors such as climate; freshwater inlow; salinity; tidal coverage; sediment type; nutrients; etc. J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal he algal lora of the Sundarbans is very poorly known; but the available information suggests that the Sundarbans has a highly diverse algal lora comprised of both benthic and planktonic forms ranging from the freshwater to marine environments. here was no previous record of algal lora of the Sundarbans before studies by Islam [3]. A few works on the phytoplankton community structure and its relation to abiotic variables in the Sundarbans river systems were hitherto studied in Bangladesh [4-8]. Various published reports on the algal lora provide only a patchy picture as they are based on short-term surveys of small isolated areas. Since algal lora play very important role in ecological context; the study of phytoplankton community structure is utmost important. Phytoplankton community structures change be inluenced by their surrounding environment; physically; chemically; and biologically; in ways which favor or disfavor their continued persistence. he study of phytoplankton community response to these variables is considered useful for interpreting hydro-chemical variations in coastal areas [9]. So the temporal and spatial composition of the phytoplankton population may act as an indicator of the water quality luctuation in response to changing environment. he present study was conducted to understand the seasonal variation of phytoplankton population with water chemistry of the major three river systems (Rupsha-Pashur; Khalpatua-Arpangachia; *Corresponding author: Dr. SM Bazlur Rahaman, Professor, Fisheries and Marine Resource Technology Discipline, Khulna University, Khulna-9208, Bangladesh, Tel: +8801914325048; Fax: +88-041-731244; E-mail: riti_rahaman@yahoo.com Received May 31, 2013; Accepted June 25, 2013; Published June 30, 2013 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/2155-9910.1000126 Copyright: © 2013 Rahaman SMB, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Volume 3 • Issue 2 • 1000126 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/21559910.1000126 Page 2 of 9 Bhola-Baleswar) in the Sundarbans. hus it can provide clues to do further research in order to get the factors responsible for disturbance in ecological imbalance of the Sundarbans; one of the unique aquatic habitats of the globe. Materials and Methods Sampling strategy Fiteen stations were selected for the examination of water quality indices. Rupsha; Passur; Shibsha; Arpangachia; Khalpatua; Malancha; Raymangal; Baleswar; and Bhola are major rivers of the Sundarbans. Sampling stations were designed to cover the three major river systems of the Sundarbans such as Rupsha-Pashur; KhalpatuaArpangachia; and Bhola-Baleswar (Figure 1). Samples were collected temporally namely in monsoon (June-October); winter (NovemberFebruary); and summer (March-May) from 5 stations of RupshaPashur river system namely (1) Karamjol (89º35.962''E; 22º25.97'N) (2) Karamjol Canal (89º35.445'E; 22º25.737'N); (3) Joymoni (89º37.757'E; 22º21.053'N); (4) Harbaria (89º36.563'E; 22º17.974'N); and (5) Harbaria Canal (89º36.985'E; 22º17.998'N); and from 6 stations of KhalpatuaArpangachia namely (1) Pashurtala (89º11’934”E; 22º14'038”N); (2) Pashurtala Canal (89º12’043”E; 22º14'077”N); (3) Kalagashi (89º14’541”E 22º12'685”N); (4) Kalagashi Canal (89°14'638"E; 22°12'392"N); (5) Nildumur (89º14’708”E; 22º14'828”N); and (6) Arpangachia (89º18’581”E; 22º12'406”N); and also 4 stations of BholaBaleswar namely (1) Bogi (89º50'21.9"E; 22º12'54.4"N); (2) Sharankhola (89º48'42.4"E; 22º12'35.6"N); (3) Supati (89º49.07'E; 22º03.442'N); and (4) Supati Canal (89º48.93'E 22º3.128' N ). Sample collection For phytoplankton community structure study; 20 L of water collected from surface water of the study area was passed through a plankton net (20 µm mesh sized; silk bolting cloth or nylon monoilament screen cloth). hen the concentrated samples were preserved with Lugol's Solution (20 g potassium iodide and 10 g iodine crystals dissolved in 200 ml distilled water containing 20 ml glacial acetic acid). For chlorophyll a estimation 200 m3 volume samples were collected in the same way using plankton net and samples for nutrient analysis were collected using a grab sampler. For nutrient analysis water samples were collected from surface; middle bottom of the particular location which was iltered immediately through pre-cleaned 0.45 µm pore-size cellulose ilters. he samples were preserved in deep frozen in the dark before analysis. Sample analysis Temperature; pH; transparency; DO; and salinity were measured Study points Figure 1: Location of the study points in Rupsha-Pashur, Khalpatua-Arpangachia, Bhola-Baleswar river systems of the Sundarbans. J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal Volume 3 • Issue 2 • 1000126 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/21559910.1000126 Page 3 of 9 in-situ and water samples collected for analyzing nutrients (NO3-; PO43-; NH4+; SiO44-); chlorophyll a and phytoplankton community composition were measured later in the laboratory. Water temperature was measured with a Centigrade Mercury thermometer; pH with a Microprocessor pH meter (HANNA instruments; pH 211); salinity with a TDS meter (HI 9635; portable multirange conductivity/TDS meter; HANNA); transparency with a secchi disc; and DO in Winkler’s method (APHA 1992). Quantitative estimation of phytoplankton was done by SedgewickRater counting chamber (S-R cell) method [6] using Labomed Imaging Device (ivu 15000 microscope). Phytoplankton genera and species were identiied [10-18]. Chlorophyll a was determined by spectrophotometric method (APHA 1992); and nutrients were measured by colorimetric methods described in Yin et al. [19]. Species richness; diversity and evenness index calculation Species richness index (d); species diversity index (H); and evenness index were calculated according to following equations • Species richness index (d) [20] d=(S–1)/ Log N Where: d=Species richness index S=Number of species in a population N=Total number of individuals in S species. • Species diversity index (H) [21] Hs=∑ Pi 1ogPi Where Hs=Diversity Index i=Counts denoting the ith species ranging from 1–n Pi=Proportion that the ith species represents in terms of numbers of individuals with respect to the total number of individuals in the sampling space as whole. • Evenness index (j) [22] j=Hs / Log S Where J=Equitability index Hs=Shannon and weaver index S=Number of species in a population Data analysis To establish diferences of the phytoplankton community descriptors among the iteen sites; one-way ANOVA was carried out. Two tailed Pearson correlation was performed to identify relation among various physico-chemical and biological parameters. Analyses were performed using the sotware package SPSS Statistics 17.0. Results Water quality Water quality parameters namely temperature; pH; transparency; dissolved oxygen; salinity; nitrate; phosphate; ammonium; silicate; and J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal chlorophyll a were determined temporally in 15 stations situated in three major river systems of the Sundarbans presented in Table 1. Temperature: Mean water temperature luctuated seasonally. In Rupsha-Pashur river system temperature ranged from 20.02°C-31°C; highest in summer and lowest in winter. In Khalpatua-Arpangachia and Bhola-Baleswar River systems it was within the range 22.17°C-30.45°C; and 19.92°C-30.25°C respectively and also showed the same kind of seasonal variability of higher values in summer and lower values in winter. pH: In Rupsha-Pashur; Khalpatua-Arpangachia and BholaBaleswar river system pH varied from 7.29-7.87; 7.31-7.82; and 6.7-7.53 respectively. In Rupsha-Pashur pH values showed a seasonal trend of variation with higher values in monsoon then showed a slight gradual reduction through winter and summer. But in Khalpatua-Arpangachia and Bhola-Baleswar river system no clear seasonal trend was observed. Transparency: In all three river systems; transparency values were very low throughout the year; but also showed a seasonal trend of variation. In both Rupsha-Pashur and Bhola-Baleswar river system; transparency was the lowest in monsoon but was found to rise gradually in winter and summer. It ranged from 8cm-36cm in RupshaPashur with highest in Harbaria during summer and lowest in Joymoni during monsoon. he transparency ranged between 18 cm and 36 cm in Bhola-Baleswar highest in Sharankhola during summer and lowest in Bogi during monsoon. But in Khalpatua-Arpangachia River system the transparency was lower in monsoon but rose in winter and again fell in summer. It was found within the range of 16 cm-66 cm; highest in Pashurtala canal during winter and lowest in Kalagashi during monsoon. Annual mean transparency also was highest (34.66 ± 18.84 cm in Pashurtala) in Khalpatua-Arpangachia. Dissolved oxygen: Dissolved Oxygen concentration (DO) luctuated spatially and temporally. In Rupsha-Pashur; KhalpatuaArpangachia; and Bhola-Baleswar river systems; DO varied from 4.37 mgL-1 to 7.37 mgL-1 (highest at Harbaria Canal in monsoon & lowest at Karamjol Canal in summer); 3.93 mgL-1 to 6.4 mgL-1 (highest at Kalagashi Canal in monsoon & lowest at Kalagashi in summer); and 4.88 mgL-1 to 5.65 mgL-1 (highest at Sharankhola in summer & lowest at Supati Canal in monsoon) respectively. In Bhola-Baleswar DO luctuated very little and not showed any seasonal trend of variation. But in Rupsha-Pashur and Khalpatua-Arpangachia a little luctuation of seasonal trend was observed with higher values in monsoon and gradually decreased over the winter and summer period. he highest annual mean value was found 6.25 ± 0.80 mgL-1 at Harbaria Canal (Rupsha-Pashur). Salinity: he highest salinity was observed (23‰) at Nildumur in winter. In Rupsha-Pashur; Khalpatua-Arpangachia; and BholaBaleswar river systems salinity ranged from 5.17‰ to 16‰ (highest at Harbaria in summer and lowest at Harbaria in monsoon); 9‰ to 23‰ (highest at Nildumur in winter and lowest at Arpangachia in summer); and 2‰ to 16‰ (highest at Supati in summer and lowest at Bogi in monsoon) respectively. In both Rupsha-Pashur and Bhola-Baleswar river system salinity showed similar seasonal variation of lower values in monsoon then rose through the period of winter and summer. But in Khalpatua-Arpangachia salinity was low in monsoon; and then rose in winter and again dropped in summer. Lowest annual mean salinity was 8.29% ± 4.50‰ (Sharankhola) in Bhola-Baleswar river system. Nitrate: In maximum sampling stations annual mean nitrate (NO3) concentrations were lower than 1 mgL-1. he highest concentration (>1 mgL-1) was observed in Bhola-Baleswar in summer. In Rupsha- Volume 3 • Issue 2 • 1000126 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/21559910.1000126 Page 4 of 9 Bhola-Baleswar River System Bogi Sharankhola Supati Supati Canal Geographical Location 89°50'21.9"E, 22°12'54.4"N 89°48'42.4"E, 22°12'35.6"N 89°49.07'E, 22°03.442'N 89°48.93'E, 22°3.128'N Temperature(°C) 25.39 ± 3.72 25.19 ± 3.76 25.95 ± 4.09 25.71 ± 4.05 pH 7.04 ± 0.21 6.87 ± 0.14 7.19 ± 0.23 7.23 ± 0.30 Transparency(cm) 25 ± 5.72 28.33 ± 6.55 25.33 ± 5.25 24.66 ± 4.11 DO(mgL-1) 5.43 ± 0.03 5.53 ± 0.08 5.29 ± 0.16 5.16 ± 0.21 Salinity 9.17 ± 5.24 8.29 ± 4.50 10.33 ± 5.72 9.72 ± 5.40 Nitrate(mgL-1) 0.603 ± 0.73 0.425 ± 0.48 0.470 ± 0.54 0.433 ± 0.49 Phosphate(mgL-1) 0.015 ± 0.005 0.029 ± 0.011 0.011 ± 0.005 0.023 ± 0.012 Ammonium( mgL-1) 0.041 ± 0.037 0.038 ± 0.018 0.064 ± 0.039 0.066 ± 0.041 Silicate( mgL-1) 16.106 ± 6.81 17.56 ± 9.22 16 ± 8.27 17.20 ± 9.56 Chlorophyll-a(µgL 1) 2.82 ± 2.28 1.71 ± 0.87 2 ± 0.87 2.33 ± 1.45 Rupsha-Pashur River System Karamjol Geographical Location Karamjol Canal Joymoni Harbaria Harbaria Canal 89°35.962'E,22°25.97'N 89°35.445'E,22°25.737'N 89°37.757'E,22°21.053'N 89°36.563'E,22°17.974'N 89°36.985'E,22°17.998'N Temperature(°C) 27.15 ± 4.48 27.32 ± 4.49 27.57 ± 4.30 27.05 ± 4.63 pH 7.55 ± 0.18 7.55 ± 0.24 7.51 ± 0.18 7.64 ± 0.14 26.78 ± 4.79 7.67 ± 0.10 Transparency(cm) 13.33 ± 2.36 20 ± 7.48 16 ± 5.66 23.33 ± 11.09 22.66 ± 8.99 DO( mgL-1) 6.1 ± 0.81 5.91 ± 1.09 5.93 ± 0.94 6.06 ± 0.76 6.25 ± 0.80 Salinity 9.96 ± 3.13 9.86 ± 3.64 9.22 ± 2.52 11.22 ± 4.51 10.54 ± 3.72 0.317 ± 0.21 Nitrate( mgL-1) 0.322 ± 0.26 0.627 ± 0.42 0.375 ± 0.27 0.404 ± 0.30 Phosphate( mgL-1) 0.449 ± 0.26 0.215 ± 0.17 0.291 ± 0.14 0.168 ± 0.12 Ammonium( mgL-1) 0.050 ± 0.025 0.052 ± 0.026 0.049 ± 0.022 0.051 ± 0.023 0.047 ± 0.025 Silicate( mgL-1) 12.19 ± 5.61 14.04 ± 4.50 11.45 ± 6.22 13.11 ± 7.36 12.19 ± 6.29 Chlorophyll-a (µgL-1) 1.38 ± 0.81 1.12 ± 0.57 1.44 ± 0.86 1.53 ± 1.04 1.63 ± 1.07 Pashurtala Pashurtala Canal Kalagashi Kalagashi Canal Nildumur Arpangachia Geographical Location 89°11'934"E, 22°14'038"N 89°12'043"E, 22°14'077"N 89°14'541"E, 22°12'685"N 89°14'638"E, 22°12'392"N 89°14'708"E, 22°14'828"N 89°18'581"E, 22°12'406"N Temperature(°C) 27.02 ± 3.40 27.17 ± 3.25 27.12 ± 3.19 27.26 ± 3.49 27.15 ± 3.57 27.21 ± 3.56 pH 7.48 ± 0.19 7.64 ± 0.09 7.63 ± 0.11 7.65 ± 0.13 7.60 ± 0.02 7.65 ± 0.16 Transparency(cm) 34.66 ± 18.84 34 ± 22.69 24.33 ± 7.93 30.66 ± 13.70 31.33 ± 10.66 29.66 ± 10.34 0.256 ± 0.10 Khalpatua-Arpangachia River System DO( mgL-1) 4.96 ± 0.50 5.02 ± 0.79 4.94 ± 0.72 5.08 ± 0.99 5.18 ± 0.84 5.04 ± 0.54 Salinity 14.91 ± 4.69 15.39 ± 4.27 14.66 ± 5.46 14.72 ± 5.90 14.72 ± 5.94 14.22 ± 6.03 Nitrate( mgL-1) 0.269 ± 0.26 0.247 ± 0.13 0.083 ± 0.03 0.123 ± 0.04 0.091 ± 0.003 0.145 ± 0.02 Phosphate( mgL-1) 0.108 ± 0.03 0.109 ± 0.03 0.099 ± 0.01 0.119 ± 0.008 0.118 ± 0.04 0.108 ± 0.03 Ammonium( mgL-1) 0.153 ± 0.19 0.117 ± 0.13 0.176 ± 0.16 0.155 ± 0.17 0.109 ± 0.12 0.121 ± 0.14 Silicate( mgL-1) 9.404 ± 6.32 10.689 ± 8.30 9.98 ± 7.26 9.98 ± 7.06 8.238 ± 5.17 8.311 ± 4.26 Chlorophyll-a(µgL-1) 0.813 ± 0.24 1.14 ± 0.91 0.87 ± 0.35 0.806 ± 0.39 1.17 ± 0.84 0.89 ± 0.52 Table 1: Annual mean values of water quality variables in Rupsha-Pashur, Khalpatua- Arpangachia and Bhola-Baleswar river systems. Pashur river system it ranged from 0.021 mgL-1 to 1 mgL-1 (highest at Karamjol Canal in winter & lowest at Karamjol in monsoon); and in Bhola-Baleswar it varied from 0.0062 mgL-1 to 1.633 mgL-1 (highest at Bogi in summer & lowest at Supati in monsoon). Both of these river systems showed a seasonal trend of lower NO3- values in monsoon and higher values in winter and summer. But in Khalpatua-Arpangachia NO3- values were found within the range of 0.05 mgL-1-0.65mgL-1 and no clear seasonal trend was observed. Phosphate: hroughout the study areas; phosphate (PO43-) concentrations were found lower than 1 mgL-1. In Rupsha-Pashur; Khalpatua-Arpangachia; and Bhola-Baleswar river systems it was observed within the range of 0.04 mgL-1-0.772 mgL-1 (highest at Karamjol in summer & lowest at Harbaria in monsoon); 0.063 mgL1 -0.161 mgL-1 (highest at Kalagashi Canal in monsoon & lowest at Pashurtala Canal in winter); and 0.005 mgL-1-0.045 mgL-1 (highest at Sharankhola in monsoon & lowest at Supati in winter); respectively. In J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal Rupsha-Pashur; and Bhola-Baleswar river systems PO43-concentrations showed no signiicant seasonal trend of variation. But in KhalpatuaArpangachia river system a seasonal trend with higher concentrations in monsoon and summer and lower concentrations in winter were observed. Annual mean PO43- value was the lowest (0.011 ± 0.005 mgL-1 in Supati) in Bhola-Baleswar river system. Ammonium: Mean Annual ammonium (NH4+) value was found the lowest (0.038 ± 0.018 mgL-1 in Sharankhola) in Bhola-Baleswar river system. NH4+ values varied from 0.015 mgL-1-0.087 mgL-1 (highest at Karamjol Canal in winter & lowest at Karamjol in monsoon) in Rupsha-Pashur river system. But in Khalpatua-Arpangachia and Bhola-Baleswar river systems NH4+ values ranged from 0.008 mgL-10.434 mgL-1 (highest at Pashurtala in monsoon & lowest at Pashurtala in winter); and 0.008 mgL-1-0.102 mgL-1 (highest at Supati Canal in winter & lowest at Supati both in monsoon ans winter) respectively. In Rupsha-Pashur and Bhola-Baleswar NH4+ values were lower in Volume 3 • Issue 2 • 1000126 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/21559910.1000126 Page 5 of 9 monsoon and higher in winter and summer. But in KhalpatuaArpangachia trends were found diferent here NH4+ values were much higher in monsoon and lower in winter and summer season. Silicate: Silicate (SiO44-) concentration was observed extremely high throughout the study area. Annual mean SiO44- concentration was found within the range of 8.238 ± 5.17 mgL-1-17.56 ± 9.22 mgL1 (highest in Sharankhola; Bhola-Baleswar and lowest in Nildumur; Khalpatua-Arpangachia). Both Rupsha-Pashur and Bhola-Baleswar showed similar seasonal trend with lower values in monsoon and higher values in winter and summer. But in Khalpatua-Arpangachia SiO44- concentrations were recorded lower in monsoon; and it rose in winter and again fell in summer. Chlorophyll: Concentration of chlorophyll a luctuated within the range of 0.24 µgL-1-3.11 µgL-1 in Rupsha-Pashur; 0.42 µgL-1-2.43 mgL-1 in Khalpatua-Arpangachia; and 0.57 µg/L-5.94 µg/L in Bhola-Baleswar. In Rupsha-Pashur and Bhola-Baleswar river systems; phytoplankton biomass showed a seasonal trend with lower values in monsoon and gradually raised levels in winter and summer. But in KhalpatuaArpangachia it was lower in monsoon; rose in winter and again dropped in summer. Annual mean biomass production was the highest (2.82 ± 2.28 µgL-1 in Bogi) in Bhola-Baleswar river system. here were signiicant diferences in water quality data (p<0.05) among river systems and also sampling sites. Phytoplankton community composition hroughout the study areas a total of 134 phytoplankton species dominated by diatoms were identiied. 99 species from 41 genera of Bacillariophyta; 18 species from 6 genera of Pyrophyta; 12 species from 9 genera of Chlorophyta; 4 species from 4 genera of Cyanobacteria; and 1 Species of Ochrophyta were present. here were signiicant diferences (p<0.05) in abundance and diversity of phytoplankton communities. In Rupsha-Pashur; Khalpatua-Arpangachia; and Bhola-Baleswar river systems; abundance varied in the range of 3.755×103 cellsL-1-1.015×105 cellsL-1 (highest at Harbaria Canal in summer & lowest at Karamjol in monsoon); 2.951×103 cellsL-1 to 4.197×104 cellsL-1 (highest at Kalagashi in winter & lowest at Kalagashi Canal in summer); and 3.246×103 cellsL-1-5.031×105 cellsL-1 (highest at Bogi in summer & lowest at Bogi in monsoon) respectively. In Rupsha-Pashur and Bhola-Baleswar similar seasonal trend was observed with lower density in monsoon and then rose rapidly through winter and summer. But in KhalpatuaArpangachia phytoplankton density was low in monsoon; rose in River System Rupsha-Pashur Khalpatua-Arpangachia Bhola-Baleswar winter and again dropped in summer. Annual average density was the highest (8.347×104 cellsL-1) in Bhola-Baleswar river system (Table 2). Species diversity: Most diverse genera were Coscinodiscus with 12 species; Protoperidinium with 11 species; halassiosira with 10 species; Chaetoceros and Paleurosigma with 7 species. Maximun species diversity was observed in Khalpatua-Arpangachia during winter (Table 3). Species diversity index; richness index and evenness index values showed spatial and temporal variation. Annual mean diversity index was highest (2.63 ± 0.49) in Khalpatua-Arpangachia. It ranged from 1.31to 4.64 (highest at Karamjol in winter & lowest at Karamjol in monsoon) in Rupsha-Pashur; 1.58to 3.85 (highest at Arpangachia in winter & lowest at Nildumur in winter) in Khalpatua-Arpangachia; and 0.66 to 4.27 (highest at Bogi in winter & lowest at Supati in summer) in Bhola-Baleswar. Richness values were found in the range of 1.21-4.99 in Rupsha-Pashur; 1.18-11.24 in Khalpatua-Arpangachia; and 1.19-5.12 in Bhola-Baleswar; and evenness index varied from 0.77 to 1.5 in Rupsha-Pashur; 0.82 to 0.97 in Khalpatua-Arpangachia; and 0.59 to1.21 in Bhola-Baleswar. All these index values showed no clear seasonal trend of variation (Table 2). hroughout the study area over all three river system Bacillariophyta dominated the community composition. It was 81.82%-100% in Rupsha-Pashur; 64.63%-96.57% in Khalpatua-Arpangachia river system. But in Bhola-Baleswar river system Bacillariophyta dominated the composition in monsoon and winter (81.81%-98.48%); but during summer Cyanophyta dominated the composition (54.42%-78.76%) (Figure 2). Discussion Phytoplankton community in the Sundarbans river systems showed with noted abundance and diversity with spatial and temporal variation to some extent. he observed diferences are likely related to local forcing functions such as transparency; salinity and in some cases with nutrient concentrations variations in addition with some unknown reasons in this study. Phytoplankton community in relation to water quality condition Concentration of nitrate (NO3-); phosphate (PO43-); ammonium (NH4+); and silicate (SiO44-) play important role as nutrient both Item Quantity Total Species 93 species Range of Variation Abundance 2.28×104 cellsL-1 (Average) 3.755×103-1.015×105 cellsL-1 Diversity Index (H) 2.39 (Average) 1.31-4.64 Richness Index (d) 2.32 (Average) 1.21-4.99 Evenness Index(j) 0.94 (Average) 0.77-1.5 Total Species 122 species Abundance 1.052×104 cellsL-1 (Average) 2.951×103-4.197×105 cellsL-1 Diversity Index (H) 2.63 (Average) 1.58-3.85 Richness Index (d) 3.36 (Average) 1.8-11.24 Evenness Index(j) 0.90 (Average) 0.82-0.97 Total Species 110 species Abundance 8.347×104 cellsL-1 (Average) 3.246×103-5.03×105 cellsL-1 Diversity Index (H) 2.80 (Average) 2.47-3.85 Richness Index (d) 2.75 (Average) 1.8-5.84 Evenness Index(j) 0.89 (Average) 0.78-0.94 Table 2: Annual mean values of phytoplankton species abundance in three major river systems. J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal Volume 3 • Issue 2 • 1000126 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/21559910.1000126 Page 6 of 9 River systems Rupsha-Pashur Seasons Species Monsoon Thalassiosira oestrupii, Thalassiosira ecentrica, Thalassiosira decipens, Coscinodiscus centralis, Coscinodiscus concinus, Coscinodiscus spiniferus, Cyclotella striata, Roperia tesselata, Nitzschia lorenziana Winter Thalassiosira wongii, Coscinodiscus granii, Cyclotella stylorum, Chaetoceros afinis, Chaetoceros debile, Skeletonema costatum, Thalassionema nitzschioides, Synedra ulna, Pleurosigma angulatum, Cylindrotheca fusiformis, Ankistrodesmus falcatus Summer Ditylum brightwelli, Anabaena cf. los-aquae and Spirulina platens Monsoon Thalassiosira ecentrica, Thalassiosira oestrupii, Thalassiosira decipens, Thalassiosira angulata, Coscinodiscus centralis, Coscinodiscus spiniferus, Coscinodiscus angsti, Coscinodiscus concinus, Cyclotella striata, Cyclotella striata, Pleurosigma angulatum, Pleurosigma directum, Pleurosigma cf. elongatum, Cerataulina bicornis, Thalassionema nitzschioides, Ceratium fusus winter Thalassiosira wongii, Thalassiosira punctigera, Thalassiosira pseudonona, Thalassiosira anguste-lineata, Coscinodiscus marginatus, Coscinodiscus wailesii, Coscinodiscus radiatus, Coscinodiscus pavillardi, Actinocyclus anulatus, Actinocyclus Pruniosus , Cylindrotheca closterium, Pleurosigma normani, Navicula meninscus, Ditylum brightwelli, Odontella sinensis, Odontella mobiliensis, Bacillaria paxillifera, Surirella gemma, Entomoneis sulcata, Entomoneis paludosa, Leptocylindrus minimus, Cladopyxis hemibrachiata, Protoperidinium biconicum, Protoperidinium subinerme, Protoperidinium claudicans, Protoperidinium leonis, Ceratium furca, Eudorina elegans, Netrium oblongum Khalpatua-Arpangachia Not available Summer Bhola-Baleswar Monsoon Thalassiosira ecentrica, Thalassiosira oestrupii, Thalassiosira decipens, Coscinodiscus centralis, Coscinodiscus spiniferus, Nitzschia behrei, Roperia tesselata, Cerataulina dentate, Eudorina elegans, Hydroductyon etc. Winter Thalassiosira lundiana, Thalassiosira wongii, Coscinodiscus angsti, Skeletonema costatum, Cylindrotheca fusiformis, Fragilaria sp., Entomoneis sulcata, Entomoneis paludosa, Chaetoceros afinis, Actinocyclus anulatus, Pleurosigma estuarii, Odontella mobiliensis, Cladopyxis hemibrachiata, Ceratium furca, Protoperidinium punctulatum, Protoperidinium subinerme, Netrium oblongum, Pediastrum simplex, Pediastrum duplex etc. Summer Anabaena cf. los-aquae, Microcystis sp, Spirulina platens, Anacystis aeruginosa etc Table 3: List of the most abundant phytoplankton genera found in the Sundarbans river-systems at different seasons. Monsoon period Winter time Summer season 100% 100% 100% 80% 80% 80% 60% 60% 60% 40% 40% 40% 20% 20% 20% 0% a 0% Ka KaC Joy Pyro 100% Har a HarC 0% Ka KaC Joy Cyano Baci Pyro Har a HarC 100% 80% 80% 80% 60% 60% 60% 40% 40% 40% 20% 20% 0% b Pa PaC Cyano Ka Chlo KaC Pyro Nil Arp 0% Pa PaC Ka Chlo 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% KaC Pyro Nil Arp Baci 100% 80% 60% 40% 20% 0% c Bo Sha Chlo Sup Baci SupC Joy Har HarC Pyro Baci KaC Pyro Nil Baci 0% b Baci KaC Cyano 100% 20% Ka Baci c Bo Sha Chlo Sup SupC Pyro Baci b Pa PaC c Ka Chlo 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Bo Cyano Sha Chlo Sup Pyro Arp SupC Baci Figure 2: Spatial distribution of relative abundance of phytoplankton at different measuring stations of (a) Rupsha-Pashur, (b) Khalpatua-Arpangachia and (c) BholaBaleswar river system during monsoon, winter, and summer respectively. J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal Volume 3 • Issue 2 • 1000126 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/21559910.1000126 Page 7 of 9 again fell in summer. Growth and production of phytoplankton in an area is a function of environmental factors prevailed in that area [29]. By pearson correlation analysis (Figure 3) we found biomass production i.e. chlorophyll a was positively correlated with transparency; salinity; and nitrate (NO3-) in Rupsha-Pashur river system. In KhalpatuaArpangachia it was positively correlated with transparency; salinity and silicate (SiO44-); and negatively correlated with temperature and phosphate (PO43-). But in Bhola-Baleswar positive signiicant correlation was observed with transparency; salinity; nitrate (NO3); ammonium (NH4+); and silicate (SiO44-). hat is; in all three river systems chlorophyll a didn’t show strong and uniform correlation with temperature and all nutrient elements. for phytoplankton growth and production. hese were estimated on a seasonal basis during the study. Results showed no uniform seasonal trend of all these nutrient elements. Nitrate (NO3-) followed a seasonal trend of lower concentration in monsoon and increased through winter and summer in Rupsha-Pashur; and Bhola-Baleswar. But in Khalpatua-Arpangagchia; it showed no clear seasonal trend. Phosphate didn’t show any seasonal pattern in Rupsha-Pashur; and Bhola-Baleswar; but in Khalpatua-Arpangachia it showed a trend of lower amount in monsoon then rose in winter and again dropped in summer. Only in Bhola-Baleswar a seasonal pattern of Ammonium (NH4+) was observed with lower values in monsoon; and gradual higher values through winter and summer. In Rupsha-Pashur silicate (SiO44-) showed a pattern of lower concentrations in monsoon and higher in winter and summer. But in Khalpatua-Arpangachia it was diferent; higher concentrations were found in winter and lower in monsoon and summer. his signiicant variation suggests the coexistence of diferent processes in water quality conditions. In marine coastal systems; there can be many sources of nutrients like upwelling; river input; sediment resuspension or remineralization; aquaculture eluents; and urban; agricultural; and industrial wastewater; thereby making it diicult to determine the relative contribution of nutrient sources to coastal water quality [23,24]. Water temperature and transparency are most important among various physical factors afecting the distribution and seasonal variation of phytoplankton growth [30]. In the present study we have found signiicant positive correlation with transparency but no signiicant positive correlation with temperature. It may be due to the cross interaction between temperature and transparency. In summer temperature and transparency both are high and biomass production was also high; but in monsoon temperature was high but low transparency limited the light penetration and as a result limited the growth [31]. Concentration of Chlorophyll a (algal biomass) is normally used as an index of the productivity [25] and trophic condition of estuaries; coastal and oceanic waters [26-28]. It relects the net result (standing stock) of both growth and loss processes. here is generally a good agreement between planktonic primary production and algal biomass. Algal biomass is associated with the visible symptoms of eutrophication. It is considered the principal variable to use as a trophic state indicator. Present study analyzed algal biomass production in terms of chlorophyll a concentration on seasonal basis. hroughout the study area highest biomass production (5.94 µgL-1) was observed in the Bhola-Baleswar river system in summer. Rupsha-Pashur and BholaBaleswar river systems showed the similar trend of seasonal variation with lower concentrations in monsoon and gradually increased value through winter and summer. But in Khalpatua-Arpangachia river system concentrations were lower in monsoon; rose in winter; and Phytoplankton abundance and biomass production both showed similar trend of seasonal variation in Rupsha-Pashur and BholaBaleswar river systems with highest production in summer but difered in Khalpatua-Arpangachia with lower production in summer. his noncompliance may be due to the late sampling time for the summer season in Khalpatua-Arpangachia (26th May-2011); when early monsoonal impact (144mm rainfall in May-2011) has already started. Silicate concentrations varied a great deal among the sites and seasons. It was found within the range of 3.201 mgL-1-26.122 mgL-1. hese higher concentrations of SiO44- may result from the shrimp-farm eluents and nutrient export from the harbor that enriched the coastal water with nutrient [32]. Oten; SiO44- acts as a limiting nutrient for diatom growth; and it could therefore control replacement of diatoms by dinolagellates in conditions of Si deiciency; which means that SiO44- Silicate* Silicate Silicate** Ammonium Ammonium Phosphate Phosphate** Nitrate** Nitrate Salinity** Salinity** DO** DO DO Transparency** Transparency** Transparency* pH** pH* pH Temperature Temperature** Temperature a -1 -0.5 0 0.5 1 b Ammonium* Phosphate Nitrate** 1st Qtr -1 -0.5 Salinity** 0 0.5 1 c 0 0.2 0.4 0.6 0.8 1 Figure 3: Pearson correlation between phytoplankton biomass and different water quality parameters in (a) Rupsha-Pashur, (b) Khalpatua-Arpangachia, and (c) BholaBaleswar river systems (* indicate signiicant correlation at 0.05 level (2 tailed) & ** indicate signiicant correlation (2 tailed) at the 0.01 level). J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal Volume 3 • Issue 2 • 1000126 Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. J Marine Sci Res Dev 3: 126. doi:10.4172/21559910.1000126 Page 8 of 9 can play an important role in phytoplankton community-structure changes [33]. High inputs of SiO44- could also cause an imbalance of the normal phytoplanktonic communities by stimulating diatom growth; some of which may have harmful efects. he salinity is also one of the main parameters that can be attributed to the phytoplankton diversity and acts as a limiting factor which inluences the distribution of planktonic community [34-37]. Generally; changes in the salinity of the brackish water habitats such as estuaries; backwaters and mangrove are due to the inlux of freshwater from land run of; caused by monsoon or by tidal variations. Presently recorded higher values in dry season could be attributed to the higher degree neritic water dominance from sea [38,39]. Diferences among sites in dissolved oxygen concentrations; as well as seasonal changes within sites; result from the balance between physical (e.g. turbulence; difusion and solubility of oxygen) and biogeochemical (e.g.; consumption; production; remineralization) processes [40]. In the study area comparatively higher values were observed in monsoon and lower in summer. In monsoon it may be due to precipitation and higher turbulence and in summer which could be a function of lower turbulence and warmer water temperatures that increase respiration and decrease solubility of oxygen. Phytoplanktonic community composition as bioindicator he phytoplankton community structures in coastal Sundarbans were determined as signiicantly dynamic with respect to spatial and temporal level. hese diferences in phytoplankton production may be related to a variety of environmental factors in aquatic environment [29]. he number of phytoplankton species identiied in major three river systems of Sundarbans; relecting the high species richness characteristics of tropical coastal areas [41]. In general diatoms dominate the whole area. But in Bhola-Baleswar Cyanophyta dominate the composition in summer. Dinolagelates are common only in Khalpatua-Arpangachia. Chlorophytes are abundant in BholaBaleswar. hese variations in species composition suggests; however hydrological connectivity exists among these river systems; it was local hydrological conditions that determined phytoplankton community structure at each site. Silicate concentrations were much higher in the study area. It probably acted as a factor for stimulating diatom growth [33]. In BholaBaleswar community composition was dominated by Cyanophyta and in summer; when highest NO3- concentrations were observed among all sites. his NO3- enriched condition probably stimulated the growth of Cyanophyta [42]. his community composition indicated high nutrient status and the presence of toxic contaminants [43-45]. It also relects the possibility of anthropogenic activities for the enrichment of nutrient [42]. Phytoplankton community structural changes are a good indicator of water quality or aquatic ecological status as they show complex and rapid responses to luctuations of environmental conditions [46]. Skeletonema costatum is an abundant species in the study areas. It is a eurytharmal and euryhaline species. So its presence is an indicator of stress environmental condition. halassionema nitzschioides was also abundant throughout the area; and its presence indicates resuspension and remineralization processes happening there. Amphora sp. and Nitzschia sp. etc. are benthic diatoms. hese were mostly abundant in Khalpatua-Arpangachia river system. heir presence indicates higher concentrations of SiO44- and resuspension of sediments. Nitzschia J Marine Sci Res Dev ISSN:2155-9910 JMSRD, an open access journal longissima and Protoperidinium were also abundant throughout the area. hese are opportunistic and indicator species of shrimp farm eluents [24,47]. Conclusion he Sundarbans which environmental conditions are highly dynamic and variable in nature is rich in phytoplankton community. Variation both in abundance and diversity is due to rainfall; transparency; salinity and nutrient concentartions. Variable water quality conditions at spatial and temporal level indicates the inluence of various climatic and local forcing functions. A relationship among local water quality characteristics with phytoplankton community is noticed. Favorable climatic condition and nutrient status of water led to a blooming condition in summer. he study will provide a number of information regarding water chemistry of the Sundarbans river systems and phytoplankton community structure in order to ind factors responsible for biodiversity loss. Acknowledgements The study was supported by the Grants for Advanced Research in Science from the Ministry of Education (MoE) of Bangladesh. The authors are thankful to the laboratory staff of Fisheries & Marine Resource Technology Discipline and Environmental Science Discipline of Khulna University for their cooperation during sample analysis. 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Estuarine, Coastal and Shelf Science 52: 91-109. Submit your next manuscript and get advantages of OMICS Group submissions Unique features: • • • User friendly/feasible website-translation of your paper to 50 world’s leading languages Audio Version of published paper Digital articles to share and explore Special features: Citation: Rahaman SMB, Golder J, Rahaman MS, Hasanuzzaman AFM, Huq KA, et al. (2013) Spatial and Temporal Variations in Phytoplankton Abundance and Species Diversity in the Sundarbans Mangrove Forest of Bangladesh. 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