Plankton diversity in Krishna River , Sangli , Maharashtra

Quantitative assessment of plankton was carried out in distinct sites of the river Krishna, district Sangli during January 2011 to December 2012. Phytoplankton diversity was observed in five groups, that is, Cyanophyceae, Bacillariophyceae, Chlorophyceae, Hydrocharitaceae and Desmidiceae including 53 species. Among them, Chlorophyceae was dominating with 22 species. Diversity of zooplanktons included, Cladocera, Rotifera, Protozoa, Nematoda, Aostraca, Schizopyrenida and Copepoda as major groups with 25 genera. Rotiferans were dominating with 9 diversified species. The relationship between plankton, diversity indices and water quality status of the river systems was discussed.


INTRODUCTION
Biological density of ecosystem was found to be the best indicator of healthy aquatic ecosystem.Aquatic contaminants as fertilizers and detergents were helpful for excessive growth of algae (Roy, 1996).Reid (1961) reported that, planktonic populations on which whole aquatic life depends is directly or indirectly governed by many biological conditions and tolerances of organisms to variations in one or more of these conditions.Phytoplankton in the aquatic community serves as a food for development and growth of zooplankton.Phytoplankton diversity appeared as a paradox (Hutchinson, 1967).Major diversity of zooplankton and phytoplankton with their composition varied with seasonal differentiation and production of meroplanktons as eggs, larvae and juveniles of the benthos, nekton, etc (Walsh, 1978).
Lotic systems are flow regime found to be one of the important factor associated with zooplankton diversity (Pace et al., 1992;Basu and Pick, 1996).Most zooplanktons are filter feeders that use their appendages to strain bacteria, algae and other fine particles of water (Thilak, 2009).Researchers described taxonomic and bivolume characteristics of riverine phytoplanktonic communities (Descy and Gosselain, 1994;Rojo and Alvarez, 1994;Reynolds and Descy, 1996).
Comparatively, lentic systems with its species composition and community structure of phytoplankton in lotic systems are not much focused on (Basu and Pick, 1996;Piirsoo et al., 2008).Species diversity in ecosystem was found to be directly related to abundance or equitability (Odum, 1983).The plankton in the ecosystem is useful as bioindicators for assessment of pollution status.
Taking account of literature and carried work, we have decided to assess planktonic diversity from river Krishna (Sangli) in terms of taxonomic richness and density which would help in understanding diversity indices of biological community.Obtained data was comparatively discussed in relation to pollution status of river Krishna.The present investigation was conducted to analyze plankton diversity mass from Krishna River, Sangli which shows level of contamination in the aquatic bodies under study.

Study area and geographical location
Sangli District is present in the western part of Maharashtra.it is geographically located at 16.8670°N latitude and 74.5670°E longitude, surrounded by Satara and Solapur districts *Corresponding author.E-mail: ashasarwade@rediffmail.com.Tel: 7588253118 or 9850148586.to the north, Bijapur District, Karnataka to the east, Kolhapur and Belgaum, Karnataka districts to the south, and Ratnagiri District to the west.Sangli district is situated around river basins of the Warna and Krishna.Sangli City is the district headquarters and total area is 8,578 km² (3,312 sq mi).The district is 24.51% urban.

Collection site
Krishna River is the major lotic system of the district, it is considered as the longest rivers in India, measuring about 1300 km in length.Approximately 105 km of riverine flow covers the district.The river originates at Mahableshwar passes through Sangli and conjoins the sea in the Bay of Bengal at Hamasaladevi (Andhra Pradesh) (Figure 1).The mean annual discharge of water is 67305 million m 3 and its drainage area is 2, 68786 sq.km of which 26.8% is in Maharashtra, 43% is in Karnataka and 29.4% is in Andhra Pradesh (Rao, 1979;CWC).

Field sampling and analysis
Samples were assessed in each season monthly from the sampling stations.Collection of plankton was made by filtering 50 L of water sample through bolting silknet No.25 (64 µ).Water samples were collected in Ambercoloured bottle to prevent discoloration of algae.Samples were preserved in Lugol's iodine solution (1v/100v) and 70% alcohol which maintain the fragile structure of animals and also helpful for settling the sample.Sedge Wick -Rafter counting cell at 100x magnifications was used for quantitative analysis of phytoplankton and zooplankton (Sedgwick, 1988).Routine analyses of physicochemical parameters were carried out.
Phytoplanktonic population in the working area showed order of dominancy among the species with regards to number as follows: Chlorophyceae > Bacillariophyceae > Cyanophyceae > Desmidiaceae and Hydrocharitaceae.

Zooplankton analysis
The major group of zooplankton observed during study period was Cladocera, Rotifera, Protozoa, Nematoda, Aostraca, Schizopyrenida and Copepoda (Figure 3).Quantified data related to species diversity showed two species of Cladocera, eight species of Protozoa, nine species of Rotifera, three species of Copepoda and only one species of Nematode, Aostraca and Schizopyrenida in assessment area.Quantified data was as follows: i) Rotifera: Rotifers, these are tiny wheel animals, considered as natural water purifiers because they perform clean up service in the slow moving aquatic bodies.In the study, Rotiferans were found dominant with 9 species, that is, Cocconeis, Ascomorpha, Diacranophorus, Branchionus Caudatus, Branchionus falcatus, Keratella quadrata, Philodina, Pterodina, Sinantheria.ii) Protozoa: Protozoans are the smallest and first aquatic organisms in the form of zooplanktons.They are second dominant group with eight diversified species in the present investigation as Chillodenella, Bursaria, Tetrahynema, Prorodon, Metapus, Verticella, Spirostomum, Slentor.iii) Copepoda: Copepods constitute planktonic group of both freshwater and marine habitats.In the present work, we found three free living groups viz.Calanoids, Cyclopoids and Harpacticoides.Copepods presented three species: Cyclopod, Nauplius and Diatomus.iv) Cladocera: Cladocerans are commonly known as water fleas.These are minute crustaceans generally ranging in size from 0.2 -5.0 mm.They belong to order Cladocera of subclass Brachiopoda under subphylum Crustacea including 11 families (Raghunathan and Suresh Kumar, 2002).Order Cladocera included two types of species during the present study, that is, Sida  and Daphnia.v) Nematoda: showed one type of species, that is, Heterodera vi) Aostraca: showed one type of species, that is, Streptocephalus vii) Schizopyrenida: showed one type of species, that is, Naegleria Among zooplankton in the study area, the order of dominance in diversified groups was as follows: Rotifera > Protozoa > Copepoda > Cladoecera > Nematoda > Aostraca > Schizopyrenida.
Plankton study showed seasonal variation in all sampling sites, as per their nutrient status, age, morphometry and other physicochemical factors.The statistical data in the present study showed that planktonic population was maximum in postmansoon and mansoon season as compared to premansoon season (Figure 4).Percent composition of phytoplankton throughout the study period showed Chlorophyceae 22%, Bacillariophyceae 11%, Cyanophyceae 10%, Hydrocharitaceae 1% and Desmidiaceae 1% (Figure 5).Relatively, zooplankton showed Protozoa 8%, Rotifera 9%, Copepoda 1%, Cladocera1%, Nematoda 1%, Schizopyrenida 1%, Anostraca 1%  (Figure 6).The study on plankton diversity showed some genera which act as bioindicators of organic pollution hence it can be said that the water body is slightly organically polluted.Tables 1 and 2 show results of phytoplankton and zooplankton analysis in the three sampling sites of river Krishna.

DISCUSSION
Distribution patterns of phytoplankton were strongly correlated with environmental factors (Lepisto et al., 2004).The relationship between phytoplankton diversity and environmental factors has great importance in assessment of pollution status (Buric et al., 2007) and identification of the main factors controlling phytoplankton in a particular water body was essential for choosing an appropriate method for maintenance of desired ecosystem state (Peretyatko et al., 2007).In the present study, we found that, species from family Chlorophyceae was dominating to others with 22 species.Chlorophyceae had algal diversity and it is one of the important indicator of water quality (Jena et al., 2008).Bhivgade et al. (2010), observed Chlorophyceae as a dominant species than other zooplanktons in Nagzari tank, Beed.Similar results were reported by Prescott (1939) and Patil et al. (1983).Venkateswarlu (1969) observed maximum proportion of Chlorophyceae during winter in river Moosi, Hyderabad.
Bacillariophyceae showed 11 species and was found to be maximum in postmansoon season and minimum in mansoon period.Thiruganamoorthy and Selvaraju (2009) documented abundant count of Bacillariophyceae in mansoon season which was lowered in premansoon.Mchugh (2003) reported Bacillariophyceae as dominant life form in phytoplanktons and largest group of biomass producer on earth which has much more estimated diversity than 100,000 species.

Sarwade and Kamble 179
In this work, Cyanophyceae showed diversity of 10 species.Barhate (1985) and Zafar (1967) considered that high percentage of dissolved oxygen is favourable for growth and development of Cyanophyceae and were recorded with seven species at Nagzari tank.Maximum growth and population was noted during the post mansoon season.Desmidiaceae showed only one species with least dominancy.Likewise Desmidiaceae, Hydrocharitaceae, also showed only one type of species in the study area.
Zooplanktons serve as important aquatic organisms, occurred abundantly in all types of aquatic habitats and has vital role in energy transfer of aquatic ecosystems (Altaff, 2004).Zooplankton constitutes important food item of many omnivorous and carnivorous fish (Shrifun, 2007).
Comparatively, Rotiferans were dominant group including nine diversified species in it, among Protozoa, Copepod, Nematode, Schizopyrenida, Anostraca and Cladocera.The density of zooplankton showed a distinct seasonal variation with each group and maximal and minimal peaks (Kiran et al., 2007).Rotifer has important role in energy flow and nutrient cycling, accounting for more than 50% of the zooplankton production in some freshwater systems (Saler and Sen, 2002).
In the present study, 9 species of Rotiferans were recorded, similarly, Jindal et al. ( 2010) observed 6 species of Rotifer in Hill stream Nogli at Rampur Bhusnar, District, Shimla.Rotifers were dominantly found in Hawkesbury-Nepean River (Kobayashi et al., 1998).Padmarabha et al. (2007) reported diversity indices of Rotifers for the assessment of pollution in Kukkarahalli and Karanji lakes in Mysore Karnataka State.Jeelani et al. (2005) documented relation of species diversity and seasonal distribution of Rotifers in Dal lake, Jammu and Kashmir.Certain species and genera of Rotifer were bioindicators of water quality, eutrophic status and productivity (Sladecek, 1983).
Depth of water, transparency, pH and predators determine the distribution and abundance of Copepods (Confer et al., 1983;Patalas, 1971).Raghunathan (1983) reported that Copepods were found in ponds, lakes, rivers and reserviours.In our study, Copepods showed only one type of species, that is, Cyclopoid.Similarly, four species of Copepods were observed by Suresh et al. (2009) from Tungabhadra River.Patil and Goudar (1989) reported seven species of Copepods from aquatic bodies of Dharwad district.One to the three species was observed by Kamble et al. (2013) from Krishna River.Some genera of Copepod and Cladocerans were cosmopolitan in their distribution, while others were restricted to some continents  (Brooks, 1959;Williamson, 1991).
According to Uttangi (2001) Cladocerans preferred to live in clear waters.Cladocerans showed only one species in the present study.Our result matches with observations of Dutta and Verma (2010) who noted three genera of Cladocera from river Chenab.Seven species were reported from Tungbhadra River (Suresh et al., 2009) whereas Kamble et al. (2013) documented 4 species of Cladocera from Krishna River ghat, Miraj, Maharashtra.Green et al. (2005) in their study reported Cladocerans abundance with five diversified species.Korovchinsky et al. (2008) carried out work on the global diversity of Cladocerans and reported that, high diversity of Cladocerans was found in littoral zone of lotic as well as temporary water bodies.
Phytoplanktons are primary producers and very useful tools for the biomonitoring of water body with regard to its pollution status (Stoermer, 1977).Some of the genera such as Oscillate, Chrococcus, Cyclotella, Scenedesmus, Navicula etc were bioindicators of pollution.
According to Venkateswaralu (2006), presence of Chlorella vulgaris indicated contamination of aquatic bodies.In the diversity, Chlorella under Chlorophyceae was found to be dominant species in the assessment indicating that water quality of selected aquatic body is slightly polluted by mixing of organic material.Our result coincides with observations of Palmer (1969) who reported that Oscillatoria, Scendesmus, Navicula are found in organic rich aquatic bodies.Some of the species like Euglena and Phacus were found in highly polluted aquatic bodies.
Among Rotifers, Branchionus was the dominant genus.Genus Brancionus indicate eutrophic aquatic body (Sladecek, 1983) and hence its abundant presence is considered as biological indicator for eutrophication (Nogueira, 2001).
Certain species and genera of rotifers were used as indicators of water quality, eutrophic status and productivity of an aquatic ecosystem (Sladecek, 1983).Hence the present study gives the season wise distribution of diversity among the phytoplankton and zooplankton from the given study area which can be useful as a data to identify one of the biological aspect of the same.

Figure 2 .
Figure 2. Season wise comparison of phytoplankton species.

Figure 3 .
Figure 3. Season wise comparison of Zooplankton species.

Figure 4 .
Figure 4. Season wise comparison chart of phytoplankton and zooplankton population.

Table 1 .
Enumeration of phytoplankton occurring at the study site throughout the year under premonsoon, monsoon and postmonsoon seasons.

Table 2 .
Enumeration of Zooplankton occurring at the study site throughout the year under premonsoon, monsoon and postmonsoon seasons.