19 Sustainable Marine Structures | Volume 02 | Issue 02 | July 2020 Distributed under creative commons license 4.0 DOI: https://doi.org/10.36956/sms.v2i2.308 Sustainable Marine Structures http://ojs.nassg.org/index.php/sms ARTICLE Spatio-temporal Variability of Dinoflagellates in Different Salinity Regimes in the Coast of Rakhine Khin Khin Gyi1 Wint Thuzar Nwe1 Zin Zin Zaw2 Khin Khin San3 1.Department of Marine Science, Mawlamyine University, Mon State, Mawlamyine, 12012, Myanmar 2.Department of Marine Science, Pathein University, Ayeyarwady Division, Pathein, 10014, Myanmar 3.Department of Marine Science, Sittway University, Rakhine State, Sittway 07011, Myanmar ARTICLE INFO ABSTRACT Article history Received: 3 January 2021 Accepted: 5 February 2021 Published Online: 30 March 2021 Regarding the spatial and seasonal variations of dinoflagellates in different salinities regimes, Prorocentrum rostratum showed a strong correlation with high salinity (≥ 29 ppt.). However, P. micans had a negative correlation with salinity. In Dinophysoids, Dinophysis caudata showed a wide salinity tolerance than other species in the group. D. miles, Ornithocercus magnificus, O. steinii, and O. thumii showed a strong correlation with salinity. In Gonyaulacoids, Ceratium furca, C. fusus, C. horridum, C. trichoceros, C. tripos, Gonyaulax polygramma, G. spinifera, and Pyrophacus magnificus showed a strong correlation with salinity. In Peridinoids, Protoperidinium depressum, P. oblongum, P. oceanicum, P. pyreforme, and Podolampus palmipes showed a strong correlation with salinity. In Gymnodinoid and Noctilucoid, Gyrodinium estuariale and N. scintillans showed a strong correlation with salinity. Keywords: Dinoflagellates Salinity Seasonal Spatial 1. Introduction Dinoflagellates are important components of the phyto- plankton in the near-shore and continental shelf environ- ments [1]. Along with diatoms, over half of dinoflagellates are photosynthetic [2,3,4]. Their ecology and biology have permitted them to be among the most successful aquatic protists, capable of surviving in different conditions of resource availability [5,6]. They are one of the major groups of primary producers that constitute the basic source of energy in aquatic food webs [7,8]. Because of the annu- al variability in species composition of dinoflagellates, these species are regularly monitored in many developed countries. In Myanmar, however, has not yet set effective monitoring programs, though there are reports of some bloom events that had been occurred in the coastal area. Since the South-West Monsoon (SWM) is the main source of climatic variations subjected to make changes in the physicochemical parameters which in turn affecting dino- flagellate community structure in the water column [9,10]. Thus, observations on salinity and species occurrence of dinoflagellates were made monthly during three consecu- tive periods 2012, 2013, and 2014. 2. Materials and Methods 2.1 Environmental Parameters of the Study Area The Rakhine coast experiences intense rainfall during *Corresponding Author: Khin Khin Gyi, Department of Marine Science, Mawlamyine University, Mawlamyine City, Mon State, Myanmar; Email: khinkhin.marinescience@gmail.com 20 Sustainable Marine Structures | Volume 02 | Issue 02 | July 2020 Distributed under creative commons license 4.0 the monsoon months of June-September causing varia- tions in salinity ranges. During the summer season (Febru- ary- May), salinity was higher (32-34 ppt.) in all stations, and the lowest salinity range, 21-23 ppt. is in the rainy season, (June-September). 2.2 Sampling Sites and Sample Collection A total of eight sampling sites were set along the Ra- khine coast. Sampling sites were plotted at Wetthe (WTE) (N17º 08´ 34.474”, E94º 27´51.226”) as station-1; MaGyi tidal creek (upper) (MGU) as station-2; MaGyi tidal creek (lower) (MGL) as station-3; MaGyi coastal area (MGC) as station-4; Kyauk-Maung-Nama (KMN) as station-5; Phoe-Kala Island (PKI) as station-6; Ngwe-Saung (NSG) as station-7 and Chithu Island (CTI) near Ngwesaung beach (N16º 49´6.243”, E94º 23´8.757”) as station-8, respectively. Among the stations, stations 2, 3, and 7 are in and near the tidal creek; stations 1, 5, and 8 are in the open coastal areas and stations 4 and 6 are at the mouth of the tidal creek. Figure 1. Sample collection sites at Rakhine coastal wa- ters. The sample collection was made by scooping a known volume of surface water using a basket and sieved with a 20 µm mesh phytoplankton net. Then transferred the wa- ter sample to the plastic bottles and immediately fixed it with formalin (final concentration 1%). While collecting the samples, water salinity was measured in-situ with a refractometer. Triplicate analysis of 1 mL sub-sample was taken from the samples and count with the Sedgwick-Raf- ter chamber. Pearson’s correlation coefficient was per- formed to analyze the relationship between dinoflagellate species and the salinity. 3. Results and Discussion 3.1 Seasonal Variations of Salinity At station 1, WTE, the highest salinity occurred in late summer, March-April, and the range was 34 ppt. in 2012; 33 ppt. in 2013 and 32-33 ppt. in 2014. During the monsoon period, July to September, salinity reaches its minimum values, 25-26 ppt. in 2012; 23-24 ppt. in 2013 and 23-25 ppt. in 2014. Mean salinities were 29.6±3.1 in 2012; 28.25±3.65 in 2013 and 28.5±2.87 in 2014. At station 2, MGU, the highest salinity occurred in late summer, March-April, and the value was the same 30 ppt. in three successive years, 2012, 2013, and 2014. Station 2 has highly fluctuated with terrestrial runoff. During the monsoon period, July to September, salinity reaches its minimum values, 13-16 ppt. in 2012; 13-19 ppt. in 2013 and 13-18 ppt. in 2014. Mean salinities were 22.92±5.79 in 2012; 23±5.24 in 2013 and 22.75±5.48 in 2014. At station 3, MGU, the highest salinity occurred in late summer, March-April, and the values were 29-32 ppt. in 2012; 32 ppt. in 2013 and 2014. During the monsoon period, July to September, salinity reaches its minimum values, 25-24 ppt. in 2012, 2013 and 24-25 ppt. in 2014. Mean salinities were 27.92±2.84 in 2012; 28.2±2.91 in 2013 and 28.2±3.1 in 2014. At station 4, MGC, the highest salinity occurred in late summer, March-April, and the values were 33-34 ppt. in three successive years, 2012, 2013, and 2014. During the monsoon period, July to September, salinity reaches its minimum values, 25-26 ppt. in 2012, 22-24 ppt. in 2013 and 23-25 ppt. in 2014. Mean salinities were 25.50±5.77 in 2012; 26.25±5.00 in 2013 and 23.93±6.24 in 2014. At station 5, KMN, the highest salinity occurred in late summer, March-April, and the values were 29-32 ppt. in 2012; 32 ppt. in 2013 and 2014. During the monsoon period, July to September, salinity reaches its minimum values, 18-21 ppt. in 2012, 24-22 ppt. in 2013 and 25- 24 ppt. in 2014. Mean salinities were 26.7±5.68 in 2012; 27.83±3.98 in 2013 and 28.08±3.04 ppt.in 2014. At station 6, PKI, the highest salinity occurred in late summer, March-April, and the values were 34 ppt. in 2012; 2013 and 2014. During the monsoon period, July to September, salinity reaches its minimum values, 26-24 ppt. in 2012, 26-23 ppt. in 2013 and 26-25 ppt. in 2014. DOI: https://doi.org/10.36956/sms.v2i2.308 21 Sustainable Marine Structures | Volume 02 | Issue 02 | July 2020 Distributed under creative commons license 4.0 Mean salinities were 29±3.81 in 2012; 29±3.51 in 2013 and 29.58±3.55 ppt.in 2014. At station 7, NSG, the highest salinity occurred in late summer, March-April, and the values were 32-33 ppt. in 2012; 33-34 ppt. in 2013 and 34 ppt. in 2014. During the monsoon period, July to September, salinity reaches its minimum values, 26-25 ppt. in 2012, 2013 and 28- 27 ppt. in 2014. Mean salinities were 29±3.19 in 2012; 29.33±3.22 in 2013 and 30.58±2.63 ppt.in 2014. At station 8, CTI, the highest salinity occurred in late summer, March-April, and the values were 32-33 ppt. in 2012; 33-32 ppt. in 2013 and 32-33 ppt. in 2014. During the monsoon period, July to September, salinity reaches its minimum values, 27-26 ppt. in 2012, 26-25 ppt. in 2013 and 24-25 ppt. in 2014. Mean salinities were 29.42±2.6 in 2012; 29.17±3.02 in 2013 and 28.58±3.55 ppt in 2014. In the present study, the mean salinities of the study pe- riod, 2012-2014, were 29 ppt., 27 ppt., 28 ppt., 30.3 ppt., 30.1 ppt., 29 ppt., 30 ppt., and 29 ppt. at stations 1, 2, 3, 4, 5, 6, 7 and 8 respectively. Salinity distributions in all sam- pling stations vary from month to month within seasons (Table 1). The mean salinity of the whole study area was 29±2.83, and the mean salinity at the sampling stations was 29±1.2 part per thousand. Figure 2. Mean salinity at sampling stations of the study areas during 2012-2014. 3.2 Spatio-temporal Variations of Dinoflagellates Prorocentroids cell density varied from 1500 to 1780 cells L-1 during the study period. The cell density of Di- nophysoids varied from 810 to 1590 cells L-1 during the summer and post-monsoon periods. Two genera such as Dinophysis and Ornithocercus were mainly composed in the Dinophysoid group which occupied 40% and 60%, respectively. Gonyaulacoids was the largest and dominant group in the study area, and the cell density ranged from 540 to 1770 cells L-1. A total of six genera were occupied in the Table 1. Mean salinity of the study area during 2012-2014. No. Months WTE MGU MGL MGC KMN PKI NSG CTI Mean SD 1. Jan 30.7 28.7 29.7 32 32.3 32 31.7 32 31.1 1.2 2. Feb 31.7 29.3 30 33.3 33 33 33 32.7 32 1.4 3. Mar 33 30 32 34 33.7 34 33.7 32.3 32.8 1.3 4. Apr 33.3 30 32 33.7 33 33.7 33.7 31.7 32.6 1.2 5. May 30.3 27.7 29.7 31.7 31.3 31 30.7 29.7 30.3 1.2 6. Jun 27.7 26 27.3 30 29.3 28.7 28.7 27.7 28.2 1.2 7. Jul 24.7 24 24.7 27.3 27.7 26 26.7 25.7 25.8 1.2 8. Aug 23.3 23.3 22.7 26 26 23 24.3 23.3 24 1.2 9. Sep 25 24.7 24.3 27.3 27 24 25.7 25.3 25.4 1.1 10. Oct 27 25.7 26.3 28.3 28 26.3 27.7 27.7 27.1 0.9 11. Nov 28.7 26.7 28.3 29.7 29 28.3 29.7 29.7 28.8 1.0 12. Dec 30 27.7 30 30.7 30.7 30.3 30.3 31 30.1 1.0 Mean 29 27 28 30.3 30.1 29 30 29 29 1.2 SD 3.2 2.2 2.9 2.6 2.5 3.6 3.0 3.0 2.8 0.2 DOI: https://doi.org/10.36956/sms.v2i2.308 22 Sustainable Marine Structures | Volume 02 | Issue 02 | July 2020 Distributed under creative commons license 4.0 Gonyaulacoids group, Ceratium 65%, Gonyaulax 10%, Pyrocystis 10%, Alaxandrium 5%, Spiraulax 5%, and Py- rophacus 5%, respectively. The Peridinoids cell density ranged from 800 to 1440 cells L-1, in which Protoperidinium composed 57%, Po- dolampus 28.6%, and Peridinium 14.3%, respectively. The Gymnodinoids and Noctilucoids group had the lowest cell density ranged from 90 to 112 cells L-1. In the study area, the cell density was normally higher during summer and post-monsoon periods when the salinity was ≥29 ppt. 3.3 Statistical Analysis Multiple correspondence analyses were made for the correlation coefficient of species and salinity changes. Sa- linity changes may vary from one station to another. In Table 2, P. rostratum showed a strong correlation with high salinity, 29-31 ppt. P. micans showed no cor- relation with salinity. P. gracile, P. lima, P. micans, and P. rostratum species were not found in station 2 where salinity is low. High cell densities were found normally at salinity, 30-31 ppt. in February-March. Table 2. Correlation coefficients of Prorocentroids and salinity. No. Prorocentroids 2012 2013 2014 1. Prorocentrum gracile± 0.14 0.67 0.60 2. P.lima± 0.16 0.79 0.19 3. P.micans- 0.02 0.34 0.45 4. P.rostratum++ 0.72 0.68 1 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated Table 3. Correlation coefficients of Dinophysoids and salinity. No. Dinophysoids 2012 2013 2014 1. Dinophysis caudata± 0.83 0.41 0.86 2. D. miles++ 0.80 0.74 0.79 3. Ornithocercus magnificus++ 0.55 0.72 0.84 4. O.steinii++ 0.74 0.71 0.99 5. O.thumii++ 0.9 0.75 0.57 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated In the Dinophysoids group, O. thumii species showed low salinity, 23-25 ppt. tolerant than other species in the group. D. miles, O. magnificus, O. steinii, and O. thumii showed a strong correlation with a wide salinity range, 23-34 ppt. O. steinii cannot tolerate low salinity than O. magnificus species. D. caudata cannot be found in low salinity of less than 22 ppt. (Table 3). The Gonyaulacoids, the largest and dominant group in the study area, and among them nine species show a strong correlation with a wide range of salinity. They were Ceratium dens, C. furca, C. fusus, C. horridum, C. trichoceros, C. tripos, Gonyaulax polygramma, and G. spinifera, respectively. G. polygramma was found in low salinity, 23 ppt. (Table 4). Table 4. Correlation coefficients of Gonyaulacoids and salinity. No. Gonyaulacoids 2012 2013 2014 1. Alexandrium concavum± 0.24 0.65 0.05 2. Ceratium breve- 0.02 0.34 0.45 3. C. dens++ 0.72 0.68 0.67 4. C. extensum± 0.48 0.41 0.76 5. C. furca++ 0.70 0.92 0.79 6. C. fusus++ 0.65 0.50 0.78 7. C.horridum++ 0.67 0.71 0.66 8. C.inflatum± 0.48 0.75 0.66 9. C.lineatum- 0.25 0.49 0.19 10. C.porrectum± 0.27 0.39 0.53 11. C.macroceros± 0.53 0.36 1 12. C.schmidtii± 0.42 0.61 0.69 13. C. trichoceros++ 0.71 0.60 0.93 14. C. tripos++ 0.89 0.75 0.51 15. Gonyaulax polygramma++ 0.65 0.71 0.74 16. G.spinifera++ 0.76 1.0 0.50 17. Spiraulax kofoidii- 0.44 0.47 0.19 18. Pyrocystis lunula± 0.08 0.45 0.07 19. Pyrophacus magnificus++ 0.53 0.53 0.67 20. P.steinii± 0.48 0.40 0.65 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated DOI: https://doi.org/10.36956/sms.v2i2.308 23 Sustainable Marine Structures | Volume 02 | Issue 02 | July 2020 Distributed under creative commons license 4.0 In the Peridinoid group, all the members of Protoperi- dinium show a strong correlation with salinity. Some Peridinium were assigned to the genus Protoper- idinium in some systematic studies. In this study, this spe- cies shows less correlation with salinity. The cell density of Protoperidinium may vary with salinity changes. Cell density will increase when the salinity increases in the water column. (Table 5). Table 5. Correlation coefficients of Peridinoid and salinity. No. Peridinoid 2012 2013 2014 1. Protoperidinium depressum++ 0.85 0.62 0.93 2. P. oblongum++ 0.57 0.53 0.92 3. P.oceanicum++ 0.51 0.69 0.99 4. P.pyreforme++ 0.64 0.71 0.62 5. Peridinium pentagonum- 0.24 0.65 -0.04 6. Podolampas elegans± 0.39 0.47 0.77 7. P.palmipes++ 0.74 0.72 0.93 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated In the Gymnodinoids and Noctilucoids group, all spe- cies show a strong correlation with salinity. The abun- dance of Gymnodinoids and Noctilucoids was lower than that of other morphospecies groups throughout the study period. Distinct temporal and spatial variations in dinofla- gellate cell densities were clear. Cell density changes may associate with the salinity concentration. (Table 6). Table 6. Correlation coefficients of Gymnodinoids and Noctilucoids and salinity. No. Gymnodinoids and Noctilucoids 2012 2013 2014 1. Gyrodinium estuariale++ 0.74 0.72 0.93 2. Noctiluca scintillans++ 0.88 0.64 0.61 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated In the Prorocentroid morphospecies group, P. rostratum shows a strong correlation with salinity while P. micans shows less correlation with salinity. P. gracile and P. lima show more or less correlation with salinity. In the Dino- physoid group, D. caudata shows less correlation with salinity during the study period, 2012-2014. The other species in the group show a strong correlation with salini- ty. In the Gonyaulacoid group, C. dens, C. furca, C. fusus, C. horridum, C. trichoceros, C. tripos, G. polygramma, G. spinifera, and Pyrophacus magnificus show strongly cor- related with salinity during the study period. Alexandrium concavum, C. extensum, C. inflatum, C. porrectum, C. macroceros, C. schmidtii, Pyrocystis lunula, and Pyropha- cus steinii show more or less correlated with salinity. C. breve, C. lineatum, and Spiraulax kofoidii show less cor- relation with salinity. In the Peridinoid group, Protoperidinium depressum, P. oblongum, P. oceanicum, P. pyreforme, and Podolampas palmipes show a strong correlation with salinity during the study period. Peridinium pentagonum, and P. elegans show more or less correlation with salinity. In Gymnodinoid and Noctilucoid group, G. estuariale and N. sintillans show a strong correlation with salinity during the study period. 4. Conclusions In terms of dinoflagellates distribution which was based on different salinity regimes, the Gonyaulacoid species, Ceratium comprises 65% and stands first in the dinoflagel- late community. In the Dinophysoid group, Ornithocercus takes 60% in species composition. Moreover, in the Perid- inoid group, Protoperidinium takes 57% in species com- position of it. In the study areas, 52.6% of dinoflagellates are strongly correlated with salinity while 13.2% shows less in correlation with salinity. Braaurd (1961) suggested that some dinoflagellate species such as Ceratium spp., Peridinium spp. and Prorocentrum spp. reproduced more actively at the lower salinities. Thus, changing salinity in nearshore areas might influence the dinoflagellate species composition. Acknowledgment The authors are indebted to Dr. Aung Myat Kyaw Sein, Rector, and Dr. San San Aye, Pro-Rector of Mawlamyine University, for their support in preparing this research work. We are thankful to Dr. San Tha Tun, Professor and Head of the Department of Marine Science, Mawlamyine University, for providing the use of departmental facili- ties. Many thanks are especially to Dr. Khin Maung Cho, Pro-Rector (Retired), Mawlamyine University, for his kind suggestions in preparing the manuscript. Also, per- mission for this work from the Department of Higher Ed- ucation, the Ministry of Education, and for facilities of the Department of Marine Science, Mawlamyine University DOI: https://doi.org/10.36956/sms.v2i2.308 24 Sustainable Marine Structures | Volume 02 | Issue 02 | July 2020 Distributed under creative commons license 4.0 is most appreciated. References [1] Sahu, G., Mohanty, A.K., Samantara, M.K., Satpathy, K.K., “Seasonality in the distribution of dinoflagel- lates with special reference to harmful algal species in tropical coastal environment, Bay of Bengal”, Environmental Monitoring and Assessment, Spring- er International Publishing Switzerland, 2014, 186: 6627-6644. [2] Gaines, G., Elbrächter, M., “Heterotrophic nutrition. In: Taylor, F.J.R. (Ed.) The biology of dinoflagel- lates”, Botanical Monograph,1987, 21: 224-268. [3] Butterfield, E.R., Howe, C.J., Nisbet, R.E., “An anal- ysis of dinoflagellate metabolism using EST data”, Protist, 2013, 164: 218-236. 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[9] D’Costa, P.M., Anil, A.C., Patil, J.S., Hegde, S., D’Silva, M.S., Chourasia, M., “Dinoflagellates in a mesotrophic, tropical environment influenced by monsoon, Estuarine”, Coastal and Shelf Science, 2008, 77(1): 77-90. [10] Sahu, G., Mohanty, A.K., Samantara, M.K., Satpathy, K.K., “Seasonality in the distribution of dinoflagel- lates with special reference to harmful algal species in tropical coastal environment, Bay of Bengal”, Environmental Monitoring and Assessment, 2014, 186(10): 6627-6644. DOI: https://doi.org/10.36956/sms.v2i2.308