Studies on Seasonal Zooplankton Community Structure of Gandak river

 

Kumari Sunita, Jai Kumar Singh

Research Scholar, Jai Prakash University, Chapra (Bihar), Associate Professor, Gopeshwar College, Hathua, Gopalganj, Bihar

 

Abstract:

The selected sites of Gandak river near Sheetalpur ghat were studied for a period of one year from June 2013 to May 2014 for regular physico-chemical parameters and zooplankton community structure. The study was designed to estimate zooplankton abundance with seasonal repeated collections. The zooplankton community was composed of 08 species of Rotifera, 07 species of Cladocera, 02 species of Copepoda and 01 species of Ostracoda. These Crustaceans were dominant Class throughout the study period. The abundance of zooplankton in the pond follows a sequence as: Rotifera > Cladocera > Copepoda > Ostracoda. There changes in quantitative and qualitative community structure were found directly correlated with abiotic factors during study period.

 

 

INTRODUCTION:

Zooplankton plays an important role in aquatic ecosystem. They link the primary producers, phytoplankton with higher trophic level organisms. Zooplankton communities respond to a wide variety of disturbances including nutrient loading and play a key role in the aquatic food chains (Sharma, 1998). Nearly all fish depend on zooplankton for their food during their larval phases and some fishes continue to eat zooplankton in their entire lives.

 

The importance of zooplankton as fish food both for adults and fry has been stressed by different workers (Fontaine and Revera, 1986).The presence and dominance of zooplankton species play a significant role in the functioning of freshwater ecosystems. Therefore, zooplanktons are considered indicators of water quality (Geiger, 1983). Zooplankton responds quickly to aquatic environmental changes (e.g., water quality characteristics, such as pH, colour, odour and taste, etc.) for their short life cycle and is therefore used as indicators of overall health or condition. During the study period, our aim was to analyze zooplankton population both qualitatively and quantitatively and the results are correlated with physico-chemical factors to get vital information for future references and better understanding of the structure and function of this important aquatic ecosystem.

 

MATERIALS AND METHODS:

The selected site of Gandak river were mostly infested with weeds. This river was selected for study of zooplanktons with four sites due to different morphometric and aquatic weeds availability, and, samples were collected between 9.00 to 11.00 AM in consequent months from June 2011. The sub-surface water was collected with the help of bucket. Zooplankton samples were taken by 50 liter water filtered with nylon bolting conical sampler and lower end of net were transferred to separate polyethylene tubes for 30 ml subsample after sedimentation.

 

The zooplanktons were preserved in 4% formalin and 4-5 drops of glycerene. Then, zooplanktons were identified with help of microscope and systematic literature (Edmondson, 1992 and APHA, 1998) for qualitative study. The quantitative study was carried with help of Sidgewick rafter cell (50 mm long, 20 mm wide and 1mm deep) and each sample was counted at least five times for average value. Then number of each zooplankton species was calculated following Welch (1948) and total number with the help of formula as:

N (org L-1) = a×b V

Where N= Number of zooplankton per liter, a= The average number of zooplankton in all counts in a counting cell of 1 ml capacity, b= The volume of original concentrate in ml (30 ml), V= Volume of original water filtered (50 litres).

 

Diversity index H̕ (Shannon and Reid, 2003) was calculated for zooplankton using the following formulae-

Shannon-Wiener index: H̕ = -Σ pi In pi

Pi = n/N, n = diversity of individual and N = total density

 

RESULTS AND OBSERVATION:

This river presents a total of 18 zooplankton species belonging to zooplanktons as Rotifera (08), Cladocera (07), Copepopda (02) and Ostracoda (01) during the study period. The species rich class Crustacea was represented by eleven species of Cladocera with Alona affinis, Bosmina longirostris, B. coregoni, Daphnia magna, D. pulex, Moina brachiata, Chydorous sphaericus and Macrothrix rosea, two species of Copepoda viz. Cyclops scutifera and C. bicuspidatus and only one species of Ostracoda i.e, Cypris subglobosa . Phylum Rotifera, being dominant was represented by 08 species including Brachionus bidentata, Brachionus calyciflorous, Brachionus quadridentata, Bryocamptus hiemalis, Keratella cochlearis, Keratella valga, Lecane luna and Notholca acuminata.

 

Although 18 species have been identified at various sites  in the Sona river, but Centropyxis aculeata, Keratella cochlearis, K. Valga, Alona affinis, Daphnia magna, Chydorous sphaericus, Macrothrix rosea and Cyclops bicuspidatus were common species at all sites.

 

 

Fig.1: Seasonal variation of zooplanktons at selected sites of Sona river near Sheetalpur Ghat.

 

Averages of all sites taken together have shown a bimodal peak, bigger peak was observed in spring months and the other smaller one was observed in summer months. The abundance of zooplankton at various sites followed a sequence:

Site I: Rotifera > Cladocera >Copepoda > Ostracoda.

Site II: Rotifera > Cladocera >  Copepoda > Ostracoda.

Site III: Rotifera > Cladocera > Copepoda > Ostracoda.

Site IV: Cladocera > Rotifera > Copepoda > Ostracoda

The overall abundance of zooplankton in the river follows a sequence as under:

Rotifera > Cladocera > Protozoa > Copepoda >Ostracoda

 

There, Rotifera showed peak density 1080 org l^-100 during the summer season, 600 org l^-100 during the autumn season,  60 org l^-100  during the winter season and 980 orgl^-100 during spring season (Figure 1). Cladocera showed maximum density 990 org l^-100 during summer season, 560 org l^-100 during autumn season,  240 org l^-100 during winter season and 830 orgl^-100 during spring season. Copepoda group exhibited maximum density 260 org  l^-100 during summer season, 180 org l^-100 during autumn season, 40 org l^-100 during winter season and 190 org l^-100 during spring season. Ostracoda group showed maximum density 40 org l^-100 during summer season, 20 org l^-100 during autumn season, 15 org l^-100 during winter season and 50 org l^-100 during spring season in this study as a whole.

DISCUSSIONS:

The trophic status of the system must be evaluated through zooplankton and other abiotic factors interact with organisms. There annual and seasonal cycle of zooplanktons is variable and plays functional response (Pennak, 1946). In general, zooplankton growth was registered during moderate temperature conditions, which may be due to regeneration and availability of minerals, being an outcome of decomposition of organic matter in sediments, and the algal food during this period are in consonance with Davis (1964).

 

The zooplankton population of Gandak river near Sheetalpur Ghat was found to be composed of Rotifera, Copepoda, Cladocera and Ostracoda.  The group Crustacea which included Cladocerans, Copepods and Ostracoda also showed unimodal curve for their population though present study during moderate temperature conditions. The crustacean group showed maximum numerical surge during warm periods and minimum during colder periods. Zooplankton diversity of Sikandarpur reservoir with 08 species of rotifers and 04 species of each of protozoans cladocerans and copepods has been observed (Kumar et al., 2007).

 

Temperature has been considered as one of the primary factors related with abundance of zooplankton in freshwaters where bottom exhibit considerable variations in temperature, especially with the progression of the warm season (Moitra and Bhattacharya, 1965). In the present study, a positive correlation between zooplankton numbers and temperature was recorded. Temperature has been reported to affect zooplankton abundance in two ways. It acts directly to hasten growth rates resulted in the increase of population densities; secondly it stimulates the growth of phytoplankton populations by providing nutrients and adequate light in the environment (Taylor, 1974). 

 

In the present study, rotifers were the most dominant group with (35%) followed by Cladocera (31%), Protozoa (24%), Copepods (8%) and Ostracods (2%). The abundance of rotifers in general and brachionids in particular has been attributed to hard and alkaline water (George, 1961). Previously in Gwalior region, Saksena and Sharma (1981) have reported thirty species of rotifers from different water bodies. Eutrophication also affects the species composition, biomass and structure of zooplankton.  In Gandak river, rotifers, cladocerans and copepods also showed moderate positive correlation with total hardness, free carbon dioxide and chlorides but high negative correlation was found with depth and electrical conductivity.  The distribution of various species of zooplanktonic organisms was not homogenous at all the stations, and there was clear cut seasonal variation of zooplankton and various physico- chemical characteristics influenced their occurrence.

 

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Received on 18.10.2017       Modified on 22.12.2017 Accepted on 16.01.2018      ©A&V Publications All right reserved Research J. Science and Tech. 2018; 10(2):137-139. DOI: 10.5958/2349-2988.2018.00020.7