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Seasonal Distribution of Phytoplankton Community in a Subtropical Estuary of the South-eastern Coast of Bangladesh

M. Mehedi Iqbal
Atmosphere and Ocean Research Institute (AORI), The University of Tokyo, Kashiwa, Chiba, Japan; bInstitute of Marine Sciences and Fisheries, University of Chittagong, Chittagong, Bangladesh

Md. Masum Billah
The United Graduate School of Agriculture Sciences, Kagoshima University, Kagoshima, Japan

Md. Nurul Haider
Department of Fisheries Technology, Bangladesh Agricultural University, Mymensingh, Bangladesh

Md. Shafiqul Islam
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong, Bangladesh

H. Rajib Payel
Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong, Bangladesh

Md. Khurshid Alam Bhuiyan
Faculty of Marine and Environmental Sciences, Department of Physical Chemistry, University of Cádiz, Cádiz, Spain

Mahmoud A. O. Dawood
Laboratory of Aquatic Animal Nutrition, Faculty of Fisheries, Kagoshima University, Kagoshima, Japan; g Faculty of Aquatic and Fisheries Sciences, Department of Aquaculture, Kafrelsheikh University, Kafrelsheikh, Egypt

Abstract/ Executive Summary:

Phytoplankton is the basic component of the aquatic food chain. To date phytoplankton communities from the coastal waters of Bangladesh have received only little scientific attention. Consequently, the abundance and community composition of phytoplankton and their relationship with some abiotic factors were studied during December 2014 to August 2015 in the Reju Khal estuary of the south-eastern coast of Bangladesh. Marked seasonal differences were observed for all of the measured abiotic factors. The density of the phytoplankton cells ranged between 9408 and 21,964 cells L−1 and had significant differences among seasons. Overall seasonal samples, 27 genera were identified of which Biddulphia was found to be the most contributory one (13.6%) followed by Coscino discus (7.9%) and Nostoc (7.8%). Marked seasonal differences in the community structure of phytoplankton were confirmed by the multivariate analyses. Further, phytoplankton populations had strong positive correlations with pH, salinity, total dissolved solids, and Secchi depth.

Keywords: Phytoplankton community; Seasonal distribution; Hydrological factors; Bangladesh

Location: The south-eastern coast of Bangladesh

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Plant

Objectives:

The present study was an effort to extend the knowledge of the seasonal distribution of the phytoplankton population in relation to some abiotic factors in the Reju Khal estuary of the south-eastern coast of Bangladesh. The outcome of the study will stimulate the knowledge of the ecology of the phytoplankton population from the subtropical coasts, especially in Bangladesh.

Methodology:

Study area The Reju Khal estuary (21°22′ to 21°15′ N and 92°4′ to 92°12′ E) is located in the Cox’s Bazar of the south-eastern coast of Bangladesh. The source of the river water is reported to be the Arakan Mountains. The Reju Khal River flows over the Bandarban districts and crosses the Ukhiathana and finally reaches the Bay of Bengal. The entire sampling was carried out from the area near to the Jaliapalong Bridge (21°17′21.06″ N and 92°3′36.40″ E) of the Reju Khal estuary. Sample collection and laboratory treatments There are three distinct seasons in Bangladesh, such as pre-monsoon hot season (March, April, May), rainy monsoon season (June, July, August, September, October), and winter season (November, December, January, and February; Islam 2003). In this study, three seasonal samples were collected during winter (December 2014), pre-monsoon (April 2015), and rainy monsoon (August 2015) seasons following Rahaman et al. (2013). Phytoplankton samples were collected from the surface (0–1 m) layer of the estuary by horizontal towing of a phytoplankton net made of bolting sink (48 μm). Three replicates of samples were collected during each sample time. The samples were treated with 5% formalin for further analysis. The settling method was carried out for the quantitative analysis of the phytoplankton. The counting of phytoplankton cells was carried out by a sedgewick rafter cell by a compound microscope following the method described by Stirling (1985). Phytoplankton samples were identified up to genus level using suitable taxonomic literature (e.g. Davis 1955; Newell and Newell 1979; Yamaji 1974). Determination of in situ water characteristics such as water temperature, salinity, pH, and water transparency was carried out using a centigrade thermometer, refractometer (TANAKA New S-100, Japan), digital pen pH meter (HANNA instruments, model HI 98107), and Secchi disk, respectively. At least three replicates were taken for each of the measured factors. Total dissolved solid (TDS) and dissolved oxygen (DO) were measured in the laboratory following APHA (2005). Statistical treatments The diversity of the species assemblage was expressed by the Shannon–Wiener index (H’), richness was measured by Margalef index (D), and evenness was measured by Pielou’s index (J) using SDR (species diversity and richness), version 4. In order to check the statistical differences among seasons, one-way ANOVA was carried out for all quantitative data (cell density of phytoplankton population and abiotic factors). ANOVA was performed by SAS (Statistical Analysis System; version 9.1). Similarity percentage analysis (SIMPER) was carried out in order to determine the most contributory species/group and to detect dissimilarity of assemblages between different seasons. The degree and test of significance between assemblages of different seasons were carried by Analysis of Similarity (ANOSIM; Clarke and Warwick 1994), the output (called test statistics, R) of which varies between –1 to + 1. The results of ANOSIM were also validated by using non-metric multidimensional scaling (nMDS; Paramo, Wolff, and Saint-Paul 2012). The details of the nMDS have been documented in the literature of Borg and Groenen (2005) and Kruskal, Wish, and Uslaner (2006). The dendrogram obtained for the phytoplankton community for different seasons represents the output of hierarchical cluster analysis based on the Bray-Curtis rank similarity matrix. Following many ecological studies (e.g. Hoque et al. 2015; Billah, Zamal et al. 2016), before going to SIMPER, ANOSIM and cluster analysis assemblages data were logarithmically transformed (Log (x + 1)) in order to reduce the variance (Zar 1996: the relationship between log x and ln x is ln x = 2.303 log x). All these multivariate analyses were carried out by the Community Analysis Package, version 4 (CAP Version 4).

Source of Information: Zoology and Ecology, 2017 VOL. 27, NOS. 3–4, 304–310

Article Link (Online Journal): https://doi.org/10.1080/21658005.2017.1387728

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Studies related to the phytoplankton population from the coastal waters of Bangladesh are sparse. Seasonal variations of the phytoplankton community in relation to some abiotic factors in the Reju Khal estuary are discussed in this paper. The most dominant phytoplankton genera in the estuary are Biddulphia, Coscino discus, and Nostoc. It seems probable that the hydrological factors in the estuary are the most favorable for these microalgae.

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