Zooplankton are indeed tiny, microscopic aquatic animals that play a crucial role in freshwater ecosystems as a vital link in the food web and contribute significantly to the overall productivity of these environments. They are performing at second trophic level in energy flow and switch over to conversion of detritus matter into edible animal food. The present study deal with the study of Zooplankton diversity and seasonal variation in Raviryala Pedda Cheruvu was conducted to check the status in the area and provide new insights into its ecology. The study was carried out during the period of two years i.e. June- 2022 to May- 2024. A total of 40 species were found in this reservoir. Among these, rotifers comprise of 20 species, Cladocera 07, Copepods 07, Ostracoda 2  and Protozoa 2. The season wise zooplankton analysis showed that the number of population was highest during winter (post monsoon), followed by summer (pre-monsoon) and lowest during rainy season (monsoon). 

Raviryala Pedda Cheruvu, Zooplanktons, seasonal diversity.

Zooplankton is crucial to aquatic ecosystems as primary consumers, linking higher trophic levels, including fish and other aquatic species, to primary producers such as phytoplankton (Dhanasekaran et al., 2017). As primary consumers, Zooplankton regulates the populations of phytoplankton by grazing, thereby preventing algal blooms and maintaining ecological balance. Zooplankton also plays a role in nutrient cycling as it recycles organic substances through feeding and excretion, thereby influencing the total productivity of freshwater systems (Butts et al., 2022). 

Zooplanktons are very sensitive to the influences of their environment and react to changes in water chemistry, temperature, and other hydrographic parameters in very obvious ways. Samples of zooplankton were taken by choosing three localities having varied environmental features. The order followed Rotifera (54.73%), and after the order came Copepoda, with a difference of 13.1, followed by Cladocera at 20.59, and then Ostracoda was 8.9%. 

The Rotifera dominated the zooplankton community, which was greatly influenced by seasonal fluctuations. Transparency, pH, conductivity, biological oxygen demand (BOD), and dissolved oxygen were important influencing factors. Ecologically zooplankton are one of the most important biotic components influencing all the functional aspects of an aquatic ecosystem, such as food chains, food webs, energy flow and cycling of matter.

MATERIAL AND METHODS      

Study Area:

SAMPLE COLLECTION SITES: Sites: 1, 2, 3 and 4

Methodology

Zooplanktons are collected bimonthly from RAVIRYALA PEDDA CHERUVU from June 2022 to May 2024.

• Samples were collected around 7.00 am to 9.30 am.

• Each sample was collected by filtering 20 litres of water through plankton net.

• Filtrate was stored in 20 ml plastic bottles and 4 per cent formalin was added for sample preservation.

• The concentrated samples were fixed with 4 per cent neutralized formalin and a few drops of glycerine, allowed to settle for overnight.

• Finally the quantitative analysis was done by using a Sedgwick-rafter cell method (Bhuiyan and Nessa 1991).

• One ml sample was transferred to Sedgwick-Rafter cell with a pipette,

• Identification and enumeration were done by a Compound microscope and enumeration of plankton by help of sedgewick-rafter chamber

• The systematic identification of plankton was made by using standard keys of Adoni (1985); Michael  and Sharma (1998); Dhanapathi (2000); Altaff (2004).

Zooplanktons: 

1. Zooplankton monthly population from June-2022 to May-2023 (Organisms/mL.).

2. Seasonal diversity of Zooplankton from June-2022 to May-2023 (Organisms/mL.).

3. Zooplankton monthly population from June-2023 to May-2024 (Organisms/mL).

4. Seasonal diversity of Zooplankton from june-2023 to May-2024 (Organisms/mL.).

            Monsoon = June-September, Post-monsoon = October-January Pre-monsoon= February-May

Zooplankton Species Copmposition: Study on zooplankton species composition at Raviryala Pedda cheruvu for a period of two years (2022-23 & 2023-24). Total 30 species of zooplanktons were identified belonging to 5 groups, among them 17 species were observed during year 2022-2023 and 13 species of zooplanktons were recorded during the 2023-2024 year.Total 30 species of zooplanktons were identified during the study period 2022-2024 out of which 16 species of Rotifers, 04-cladocera, 05-copepods, 02-ostracods and 03 were protozoans. 

Rotifers:

    The quality of zooplanktons:

Overall population Rotifers during 2022-2023 were, 1002 organisms/mL, cladocera-801 organisms/mL, Copepods 701 organisms/mL, Ostracods 441 organisms/mL and protozoans were 333 organisms/ mL. During 2023-2024 Rotifers were 1044 organisms/mL, cladocerans 841 organisms/mL, copepods 747 organisms/mL, Ostracods 508 organisms/mL and protozoans 374 organisms/mL.  Seasonal deviations of zooplanktons recorded as 678 organisms/mL (monsoon), 1401 organisms/mL (post-monsoon and 1205 organisms/mL (pre-monsoon) during 2022-2023 year. Similarity in 2023-2024 were 725 organisms/mL(monsoon), 1475 organisms /mL (post-monsoon) and 1314 organisms /mL (pre-monsoon).

The present investigation of zooplanktons includes five groups were found i.e. rotifers, cladocerans, copepods, ostracods and protozoa and the total number of species 30 belongs to five groups of zooplankton were identified. The monthly variation of zooplankton during the 2022-2023, 2023-2024 is depicted in table numbers: 6, 7,9 and10  The highest number of rotifers in month of January  (132 organisms /mL), lowest number were in month of July (48 organisms/mL, cladocerans were highest in January (112 organisms/mL, lowest number in September (36 organisms /mL), copepods were high number in may (96 organisms/mL), lower in September (31 organisms/Ml), ostracods were high in may (60 organisms/mL), lower number in September (18 organisms/mL) and highest number  of protozoans in January(39 organisms/mL), lowest number in June, august (20 organisms /mL during 2022-2023.

The highest number of rotifers in month of December (137 organisms/mL), lowest number were in month of July and September (50 organisms/mL, cladocerans were highest in January (117 organisms/mL, lowest number in September (39 organisms/mL), copepods were high number in may (104 organisms/mL), lower in September (34 organisms/mL, ostracods were high in may (68 organisms/mL), lower number in September (21 organisms/mL) and highest number  of protozoans in January (43 organisms/mL), lowest number in  august (22 organisms/mL during 2023-2024. The present revealed 40 species of zooplanktons in Raviryala Pedda Cheruvu.

The percentage of zooplankton groups in seasonal wise during June-2022 to May-2023 was highest percentage during winter (post-monsoon) 42.66%, next 36.6% in summer (pre-monsoon) and low in rainy (monsoon) was 20.64%. The low number of zooplankton in monsoon due to the fall in temperature, low light penetration and heavy water flow wash off the surface. The percentage of different zooplanktons classes noted during June-2023 to May-2024 were Rotifers 29.7%, Cladocera 23.93%, copepods 21.25%, ostracods 14.45% and protozoa 10.6 percent respectively during this period. The percentage of zooplankton groups in seasonal wise during June-2023 to May-2024 was highest percentage during winter (post-monsoon) 41.97%, next 37.39% in summer (pre-monsoon) and low in rainy (monsoon) was 20.63%. 

Dominate number of rotifers, copepods were mainly because of small size, with short life cycles and wide tolerance to a variety of environmental factors. Overall population of Rotifers during 2022-2023 were, 1002 organisms/mL, cladocera-801 organisms/mL, Copepods 701 organisms/mL, Ostracods 447 organisms/mL and protozoans were 333 organisms/mL. During 2023-2024 Rotifers were 1044 organisms/mL, cladocerans 841 organisms/mL, copepods 747 organisms/mL, Ostracods 508 organisms/mL and protozoans 374 organisms/mL. The seasonal deviations of zooplanktons recorded as 678 organisms/mL (monsoon), 1401 organisms/mL (post-monsoon 0 and 1205 organisms/mLb(pre-monsoon) during 2022-2023 year. Similarity in 2023-2024 were 725 organisms/mL (monsoon), 1475 organisms/mL (post-monsoon) and 1314 organisms/mL (pre-monsoon).

Zooplankton diversity and abundance of this lake showed significant seasonal variations, with influenced by environmental factors like temperature, rainfall, and food availability. In this lake zooplankton populations were more diverse and abundant during post-monsoon, due to more favorable for growth and reproduction, and less diverse during rainy seasons due to dilution and other factors. Different zooplankton groups, above mentioned such as rotifers, cladocerans, and copepods, may exhibit varying responses to seasonal changes. Rotifers, were often abundant in eutrophic (nutrient-rich) waters and it showed that water quality indicators. Monitoring zooplankton diversity and abundance of this lake clearly provided valuable insights into the impacts of climate change and other environmental factors on aquatic ecosystems.

Scope of this study: The scope of zooplankton diversity in a lake ecosystem is broad and reflects the complex interplay between various biotic and abiotic factors. Understanding this diversity is essential for assessing the health of the lake and managing its resources sustainably.

Ecosystem Management: Understanding zooplankton diversity helps in managing water quality, controlling harmful algal blooms, and maintaining a healthy aquatic ecosystem. 

Conservation Efforts: Knowing which species are present and how they respond to environmental changes is essential for developing targeted conservation strategies.