Fish Assemblage Patterns: Temporal Distribution Structure and Influence of Environmental Variables in the Karnafully River Estuary, Bangladesh  

Md. Mostafa Shamsuzzaman1 , Partho Protim  Barman1 , Arif Hasan1 , Md. Rashed-Un-Nabi2
1. Department of Coastal and Marine Fisheries, Faculty of Fisheries, Sylhet Agricultural University, Sylhet-3100, Bangladesh
2. Institute of Marine Sciences and Fisheries, University of Chittagong, Chittagong-4331, Bangladesh
Author    Correspondence author
International Journal of Marine Science, 2016, Vol. 6, No. 12   doi: 10.5376/ijms.2016.06.0012
Received: 03 Oct., 2015    Accepted: 28 Mar., 2016    Published: 28 Mar., 2016
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Barman P.P., Shamsuzzaman M.Md., Hasan A., and Rashed-Un-Nabi Md., 2016, Fish assemblage patterns: Temporal distribution structure and influence of environmental variables in the Karnafully River Estuary, Bangladesh, International Journal of Marine Science, 6(12): 1-8 (doi: 10.5376/ijms.2016.06.0012)

This research aims at studying the temporal distribution of fish assemblage in the Karnafully river estuary, Bangladesh. To study the fish assemblage catch from Estuarine Set Bag Net (Behundijal) as well water samples were collected in four seasons (winter, pre-monsoon, monsoon and post-monsoon) from March 2013 to February 2014. Multivariate analyses were performed using the software PRIMER V6 and Canonical Correspondence Analysis (CCA) was done using the PAST software. The present study identified 41 fish species, where Harpadon nehereus (20.54%) was the most dominant fish species. The Shannon-Wiener diversity index (2.67±0.05), Margalef richness index (5.14±0.64), Pielou’s evenness index (0.96±0.007) was high, while Simpson dominance index (0.95±0.002) was low in the monsoon season, which indicates monsoon had high fish diversity than the other seasons. At the similarity of 50.5%, three groups were attained while, monsoon-2 showed separate clustering from other groups. The Non-metric Multidimensional Scaling (nMDS) showed 20% similarity in all seasons based on Bray-Curtis similarity matrix. The CCA ordination indicated that salinity and DO were the two most important environmental parameters shaping the fish assemblage structure in the Karnafully river estuary.
Karnafully river estuary; Fish assemblage; ANOSIM; SIMPER; CCA

Estuaries are the meeting places of freshwater and saltwater a dynamic environment (Eick and Thiel 2014). It is not only providing important economic functions in transportation, industry and tourism but also helping drainage of domestic and industrial waste (Hossain et al, 2012). It is dominated by marine species but offers habitat for both freshwater and marine species (Thiel 2011). High levels of productivity in estuary are often related to environmental variables like salinity, water depth, temperature, turbidity and DO (Dissolved Oxygen) (Menezes et al, 2013; Potter et al; 2013). Estuary provides nursing, feeding and spawning grounds for numerous fish species (Alam et al, 2013; Sukumaran et al, 2014). These fish assemblages change continually in time and space (Tang et al, 2015). The Karnafully estuary plays an important role on both economic and ecological function for Bangladesh. It is one of the most important estuaries providing spawning, nursing, feeding ground for numerous fish species and active fishing done here. However, there are just a few sprinkled researches on different biological aspects of the Karnafully estuarine system. The current study was designed to fulfill the gap of those previous studies. Hence, the present study was undertaken to investigate the effect of physico-chemical parameters of water on seasonal variation of fish assemblage in the Karnafully river estuary.
Materials and Methods
The Karnafully River is the principal river originated from the Lushai Hills of Mizoram (India), flowing through Chittagong city and finally discharging into the Bay of Bengal. The geographical location of the study area is latitude "21o16′32′′ N to longitude 91o50′48′′ E" known as 11 no. ghat (Figure 1). Fish samples were collected by using Estuarine Set Bag Net (ESBN, Figure 2), locally called Behundijal from March 2013 to February 2014 in four seasons proposed by Mahmood et al (1992) which were winter (December-February), Pre-monsoon(March-May), Monsoon(June- September) and Post-monsoon(October-November). Sampling was done during the full moon and new moon, because in this time fish abundance is higher, according to local fishermen’s perciption. Around 1kg of unsorted fish was directly collected from ESBN catch and identified up to species level proposed by Hossain et al (2007), Howlader (1976) and FishBase (2013). Environmental parameters were recorded by using centigrade thermometer for water temperature, Refractometer (NewS-100, TANAKA, Japan) for salinity, DO meter (HI 9142, HANNA Instruments) for DO and pen pH meter (s327535, HANNA Instruments) for alkalinity. Water transparency measured by using a 20cm diameter secchi disc.


Figure 1 Location of the study area (Karnafully river estuary)



Figure 2 Sampling gear Estuarine Set Bag Net (ESBN) used for sample collection


Diversity of the species assemblage was analyzed by the Shannon-Wiener index (H′) (Shannon 1949), species richness by Margalef index (d) (Margalef, 1968), evenness by Pielou’s index (J′) (Pielou, 1966), and dominance was measured by Simpson index (c). A one-way analysis of variance (ANOVA) was used to test for significant difference in environmental variables, different diversity index and fish abundance among seasons. Prior to ANOVA test, all variables were tested for normality and homogeneity using “Kolmogrouv Smirnov test” and “Levene’s test” (Akin et al, 2005). One-way analysis of Similarity (ANOSIM) was used to conclude the significance of temporal variation in the structure of fish assemblage. The test based on a Bray-Curtis similarity matrix and were calculated using log(X+1) transformed data. Similarity percentages analyses (SIMPER) were used to observe the percentage contribution of each taxon to the average dissimilarity between the various season combinations.  Non-metric multidimensional scaling (nMDS) was performed to investigate similarities among fish abundance. For descriptive statistics and ANOVA test SPSS software V11.5 was used. All the multivariate analysis were performed using the software PRIMER V6 (Plymouth Routines Multivariate Ecological Research). Canonical correspondence analysis (CCA) was used to investigate the relationship between species assemblage composition and environmental variables using PAST2.16software.


Results and Discussion

Environmental variable
Environmental variables observed and recorded during this study are summarized in Table 1 and illustrated in Figure 3. Water temperature varied from 25.33±0.57°C (winter) to 30.00±0.58°C (pre-monsoon), salinity from 13.33±1.52ppt (Monsoon) to 20.33±0.57ppt (pre-monsoon), water transparency from 18.93±1.11cm (Monsoon) to 22.44±0.72cm (Post-monsoon), DO from 5.21±0.01mg/L (monsoon) to 6.13±0.02 mg/L (winter) and water pH from 5.33±0.57 (winter) to 6.33±0.28 (pre-monsoon). During pre-monsoon air temperature remained higher than other seasons which might lead to high water temperature and high evaporation rate, that’s why water salinity was high in pre-monsoon. On the other hand, due to heavy rainfall and mixing of runoff water, transparency was very low in monsoon compared with other seasons and caused low DO level. Similar trends were also recorded by is Rahman et al (2014) in Kaptai Lke, Bangladesh and Shukla et al (2013) in Maheshara Lakein Gorakhpur, India.



Table 1  Mean value of environmental variables in different seasons in the Karnafully river estuary



Figure 3 Environmental variables indifferent seasons in the Karnafully river estuary


Species Abundance
From the Karnafully River estuary a total of 1193 individual of fin fishes were collected during the study (Table 2) which represented 41 species. The most dominant taxa was H. nehereus (20.54%). The total abundance of species in each season ranged from 17 (post-monsoon) to 31 (monsoon). Kamal (2000) and Nabi et al (2011) reported 46 and 45 finfish species in Karnafully and Bakkhali river estuary respectively, which coincide with the present result.
Species Diversity
Different diversity index were used to calculate species diversity in the Karnafully river estuary, Bangladesh (Figure 4). The Shannon-Wiener diversity index (H') ranged from 2.41±0.10 (winter) to 2.67±0.05 (monsoon), Margalef richness index was from 5.14±0.64 (monsoon) to 4.12±0.30 (post-monsoon), Pielou’s evenness was from 0.96±0.007 (monsoon) to 0.93±0.008 (pre-monsoon), Simpson dominance was from 0.97±0.012 (winter) to 0.95±0.002 (monsoon). Significant difference observed for Shannon-Wiener diversity (p=0.02) and Pielou’s evenness index (p=0.009) whereas no significant difference observed for Margalef richness (p=0.07) and Simpson dominance index (p=0.12) among the seasons.



Table 2 Fish species recorded in the Karnafully river estuary in different seasons showing relative %contribution to the total abundance



Figure 4 Temporal variation of species diversity index of Karnafully river estuary


Monsoon season shows high diversity value, richness and evenness value, but low richness value compared with other seasons which indicated monsoon season had high species diversity than others. However, monsoon is the breeding season for many fish species as for example H. nehereus, P.microdon, so that in this time greater assemblage of fish species was observed in estuary, that’s why monsoon season showed high fish diversity (Nabi et al; 2011).
Species assemblage
Analysis of similarity (ANOSIM) was found significant difference among seasons (Table 3) where global R= 0.796 and p=0.07.  SIMPER analysis showed average similarity of species was 66.70% in winter, 66.47% in pre-monsoon, 64.16% in monsoon, 78.36% in post monsoon and most contributing species were J.macropterus(22.73%), P.microdon(17.04%), P.microdon(18.97%) and J.macropterus (14.44%) respectively (Table 4). Non-metric Multidimensional Scaling (nMDS) analysis was performed to investigate similarities among fish abundance. Three marked separation was observed in the abundance of fish in different seasons (Figure 5).Through cluster analysis, at 50.5% similarity three groups were attained while, monsoon-2 showed separate clustering from other groups. nMDS showed 20% similarity for all seasons. Only postmonsoon-1 and postmonsoon-3 season showed 80% similarity together shown in Figure 5.


Table 3 Result of ANOSIM & SIMPER analysis of fish abundances between different seasons 



Table 4 Average similarity of contributing species in each season using SIMPER analysis



Figure 5 Dendrogram showing cluster and nMDS analysis based on Bray-Curtis similarity matrix catch composition in 2D ordination


Canonical correspondence analysis (CCA)

CCA provided insight into the relationship between the fish assemblage and environmental variables (Marshall and Elliott, 1998). Results obtained from CCA were plotted in Figure 6. Species plotted closer to the vector had stronger relationship with them. The CCA ordination indicated salinity and DO were two most important environmental parameters shaping species assemblage structure in the Karnafully River estuary than the other variables. From the figure it is clear that S1=H. nehereus S2=P. microdon, S3=C. ramkorati, S8=O. rubicanduy are strongly influenced by the water salinity. Salinity is strongly allied with distribution of estuarine fish communities as reported by many authors (Nabi et al 2011 and Akin et al 2005) which are homologues with the present findings. As shown in CCA ordination S1=H.nehereus, S2=P.microdon, S3=C.ramkorati, S4=J. macropterus, S5=E.tetradactylum, S6=C.dussumieri, S7=C. lingua, S8=O.rubicanduy, S9=M.gulio, S10=S.phasa, S11=T. vagina, S12=G.chapra, S13=P.paradiseus.


Figure 6 The CCA ordination of species abundance and environmental parameters


The seasonality of the environmental conditions co-occurred with the major variations of the fish assemblage. Seasonal variations occurred not only in total abundance and diversity, but also in the structure of the species assemblage of the Karnafully river estuary. H.nehereus was found as most dominant fish in the Karnafully River contributing 20.540% in total species composition, while other species showed equal distribution throughout the seasons. Winter season showed the lowest species diversity, while monsoon season showed highest species diversity during the study. Salinity and DO were two most important variables shaping the species assemblage in the Karnafully river estuary. Species diversity was low, that probably the Karnafully river estuary is highly polluted by industrial pollution and high discharge of polluted material from oil tanker, fertilizer factory, Chittagong City Corporation which is degrading the ecological condition of the Karnafully river estuary water.
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