Abstract

Zooplanktons are tiny organisms that play a crucial role in aquatic ecosystems and are considered bio indicators of water quality and purity. In this study, the composition and diversity of zooplankton in Bhosga Lake of Kalaburagi District were assessed using a standardized methodology. Sampling was carried out at six selected stations from July 2020 to June 2021, and monthly variations and biodiversity indices of zooplankton were observed. The study revealed a total of 27 species of zooplankton, with Phylum Rotifers comprising 16 species, Cladocera 6, Copepoda 3, and Ostrocoda 2 species. A season-wise analysis showed the highest number of species during summer and the lowest number of species during the rainy season. Among rotifers, Branchionuscaudatus was the most abundant species. Bhosga Lake is home to many migrating bird species, fish, aquatic plants, and other insects, but is surrounded by human settlements and is prone to pollution due to various activities such as washing clothes, bathing animals, and dumping domestic waste. The physicochemical profile and zooplankton diversity indicate that Bhosga Lake is eutrophicated, and therefore, the conservation of faunal diversity and water quality requires serious attention and reclamation efforts.

1. Introduction

Aquatic ecosystems are essential components of the planet, providing numerous ecological and socioeconomic benefits to humans ¹. Zooplankton, as a key group of aquatic organisms, plays a significant role in maintaining the health and function of these ecosystems ². They are not only important components of the food chain but also serve as bio indicators of water quality and purity ³. Bhosga Lake, located in the Kalaburagi District of Karnataka, India, is an important freshwater ecosystem that supports a diverse array of aquatic fauna and flora, including migratory birds, fish, and various insects ⁴. In this study, we aimed to assess the zooplankton composition and diversity in Bhosga Lake using a standardized methodology. This study provides a baseline for future research on zooplankton diversity and water quality in Bhosga Lake, which could inform conservation efforts and management strategies for this important freshwater ecosystem ⁵. Zooplanktons are significant indicators of water quality and the health of the environment and play a critical role in the operation of aquatic ecosystems. ³. Understanding the seasonal functions of zooplankton populations can be done using a variety of quantitative parameters, such as density, biomass, and biochemical substances. Assessing the function of zooplankton in a particular ecosystem requires an understanding of these characteristics ². In the past, tropical and subtropical nations like India have conducted studies on the ecology and seasonal distribution of zooplankton ^{6, 7}. Through their heterotrophic activity, zooplanktons play a significant role in the cycling of organic matter in aquatic ecosystems and can be used as bio indicators of environmental quality ⁸.

Bhosga Lake is an important freshwater ecosystem supporting diverse faunal and floral communities. Zooplanktons, as a crucial component of aquatic ecosystems, plays a vital role in nutrient cycling and are considered as bio indicators of water quality and purity ^{10, 12, 13}. To better understand the ecological function of zooplankton populations in Bhosga Lake, the composition and diversity of zooplankton were assessed using a standardized methodology ⁵. Previous studies have emphasized the importance of understanding the role of zooplankton populations in aquatic ecosystems through various quantitative parameters such as density, biomass, and biochemical compounds ^{11, 14, 15}. Studies conducted in tropical and subtropical regions have shown that zooplankton populations are sensitive to changes in environmental conditions and can serve as bio indicators of water quality ^{2, 7}. The present study focuses on assessing the diversity of zooplankton in Bhosga Lake and its implications for water quality and conservation. The results of this study will shed significant light on the ecological role played by zooplankton populations in Bhosga Lake and the necessity of conservation efforts to preserve the ecosystem's faunal diversity and water quality.

2. Materials and Methods

The study was conducted at Bhosga Lake, located in Kalaburagi District, Karnataka, India (16°45'58"N, 76°08'19"E) (Figure 1). Six sampling stations were selected, and monthly samples were collected from July 2020 to June 2021 using a standard plankton net (mesh size of 55 µm). The net was towed vertically from the surface to the bottom for duration of five minutes. The samples were preserved in 4% formalin solution.Sampling was conducted at six selected stations from July 2020 to June 2021, and monthly variations and biodiversity indices of zooplankton were observed.

The preserved samples were transported to the laboratory and analyzed using a stereomicroscope (Olympus SZX7). The zooplanktons were identified to the species level using standard taxonomic keys ^{16, 18}. The species richness, diversity indices (Shannon-Wiener and Simpson indices), and evenness indices were calculated following the methods described by ¹⁷.

Standard techniques were used to measure the lake water's physicochemical characteristics, including temperature, pH, total dissolved solids (TDS), electrical conductivity (EC), dissolved oxygen (DO), and biochemical oxygen demand (BOD) ⁹.

One-way analysis of variance (ANOVA) and Tukey's post-hoc test were used to analyze the zooplankton data in order to identify any significant variations in species composition and diversity between sampling stations and seasons. Utilizing the software R, all statistical analyses were completed (version 4.0.5).

3. Results

The study's findings show that a total of 27 zooplankton species were identified during the study period, with 16 species belonging to the phylum Rotifers, 6 to Cladocera, 3 to Copepoda, and 2 to Ostrocoda. Branchionuscaudatus was discovered to be the most prevalent species of rotifers. According to a seasonal analysis, there are the most species during the summer and the least during the rainy season. The physicochemical profile of Bhosga Lake and zooplankton diversity showed that the lake is eutrophicated and prone to pollution due to various human activities. These findings are consistent with previous studies on the role of zooplankton in aquatic ecosystems, as well as the ecological distribution of zooplankton in tropical and subtropical regions ^{6, 7}. The results also highlight the importance of considering the diversity and composition of zooplankton in assessing water quality and the conservation of faunal diversity in freshwater ecosystems. Overall, the study provides valuable insights into the zooplankton diversity of Bhosga Lake, which can be used to inform future conservation and management efforts.

Table 1 the table provides information on the relative abundance of different species from various classes and phyla present in a water sample. The sample includes species from the phyla Rotifera, Cladocera, Ostracoda, and some unspecified species. The table is organized by phylum, class, species, and their corresponding relative abundance, expressed as a percentage. The most abundant species is Brachionuscalyciflorus from the phylum Rotifera and class Monogonata, representing 24.4% of the total abundance. Other abundant species include Brachionus angularis, Keratellacochlearis, Daphnia similis, and Eucyclops sp. The majority of the species belong to the class Monogonata and Cladocera, with a smaller number of species belonging to Copepoda and Ostracoda. The table provides a useful summary of the distribution and relative abundance of different species in the water sample, which could be valuable for further ecological analysis.

ROTIFERA

1. Keratellacochlearis

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Ploima

Family: Brachionidae

Characters

1. In the entire world, it is the most prevalent and widespread species.

2. Three pairs of spines are present at the anterior end.

3. It has a protective outer cuticle that resembles an oval lorica shell.

2. Brachionuscalyciflores

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Ploima

Family: Brachionidae

Characters

1. Posterior spines are frequently present, and anteromedian spines have broad bases.

2. Lorica is a seamless, transparent substance that looks like one solid piece.

3. It is frequently used as a model organism in evolutionary biology and toxico-ecology.

3. Brachionuscaudatus

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Ploima

Family: Brachionidae

Characters

1. Two small anteromedian spines; anteromedial and antelateral spines are either absent or greatly diminished.

2. There are two posterior spines that diverge.

4. Brachionusangularis

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Ploima

Family: Brachionidae

Characters

1. The angular brachionus is a detritovore.

2. Absence or severe reduction of the two small anteromedian spines, the anterior medial and anterior lateral spines.

5. Brachionusbidentata

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Ploima

Family: Brachionidae

Characters

1. Well-developed anterointermediate spines.

2. Due to their ease of mass production, brachionus spines are used to feed hatchery-raised larval fish in place of wild zooplankton.

6. Asplanchnapriodonta

Kingdom: Animalia

Phylum: Rotifera

Classs: Monogononta

Order: Ploima

Family: Asplanchnidae

Characters

1. It can be seen in a freshwater eutrophic lake.

2. It has asexual reproduction.

3. It can be located in four meters underwater.

7. Trichocercamulticrinis

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Ploima

Family: Trichocercidae

Characters

1. The ovoid body has a single anterior mucro that is frequently connected to eutrophic water.

2. Trichocera use the mucus secretions from their pedal glands to cling to surfaces.

8. Lepadella patella

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Ploima

Famliy: Brachionidae

Characters

1. The dorsal plate is strongly arched.

2. Dorsal plate has a stippled collar.

3. The longest foot segment is at the end.

9. Filiniaterminalis

Kingdom: Animalia

Phylum: Rotifera

Class: Monogononta

Order: Flosculariaceae

Family: Fillinidae

Characters

1. It mostly happens during the winter and spring.

2. Regarded as a stenotherm that is cold.

CLEDOCERA

1. Ceriodophniadubia

Kingdom: Animalia

Phylum: Arthropoda

Order: Branchiopeda

Sub order: Cladocera

Family: Daphniidae

Characters

1. Rostrum is missing, and the head is small and downcast.

2. There is a cervical sinus.

3. Two pectonmorphotypes of the postabdominal claw with a central pecten have been discovered in Ceriodaphniadubia.

2. Diaphanosomaexcisum

Kingdom: Animalia

Phylum: Arthropoda

Class: Branchiopoda

Order: Cladocera

Famliy: Sididae

Characters

1. It belongs to the genus' most widely distributed species in the tropics and subtropics.

2. It is distinguished by a large, rectangular head, a well-developed ventral and dorsal carapace, and two spines close to the posterior carapace margin.

3. By virtue of its second biramous antennae, it can be distinguished from other cladocera species with ease.

3. Moinamacrocopa

Kingdom: Animalia

Phulym: Arthropoda

Class: Branchiopoda

Sub order: Cladocera

Family: Moinidae

Characters

1. Large, distal forked teeth on the post abdomen make up the antennae.

2. There is no supraocular depression.

3. Occasionally found in saline water in small ponds or pools.

COPEPODA

1. Copepodanauplius

Kingdom: Animalia

Phylum: Arthropoda

Sub-phylum: Crustacea

Sub class: Copepoda

Characters

1. It frequently occurs in young crustaceans.

2. Barnacles can occasionally be found on the nauplii of different species, and they can be easily distinguished because they have distinctive "horns."

3. Nauplii serve as a separate source of food for fish and other predatory invertebrates.

2. Tropocyclopprasinus

Kingdom: Animalia

Phylum: Arhropoda

Sub phylum: Crustacea

Sub class: Copepoda

Order: Cyclopoida

Characters

1. Species have 12 antennule segments, a fifth leg that is one distinct segment with three terminal spines or setae, and relatively long caudal rami.

2. It is based on differences in caudal rami and leg 4 attributes, such as related setae and spines, in proportion.

3. Epischuralacustris

Kingdom: Animalia

Phylum: Arthropoda

Sub phylum: Crustacea

Sub class: Copepoda

Family: Temoridae

Charecters

1. Three caudal setae are present.

2. E-lacustris feeds by filteration and prefers large, conical phytoplankton made of gelatin.

3. E-lacustris exhibits both horizontal and vertical migration in its diet.

Table 2 summarizes the biodiversity indices of zooplankton in Bhosga Lake. The Margalef’s richness index was found to be 4.12, indicating that the lake has a relatively diverse population of zooplankton species. The Shannon-Wiener index was calculated to be 1.64, indicating moderate diversity of zooplankton in the lake. The Simpson’s diversity index was calculated to be 0, indicating a low level of evenness among the zooplankton species present in the lake. Overall, the results suggest that while Bhosga Lake has a diverse population of zooplankton species, the distribution of these species is uneven.

Bubble Graph Plot Figure 17 represents the Biodiversity Indices in Bhosga Lake: Margalef's richness index and Shannon-Wiener index are plotted on the x-axis and y-axis, respectively, with the size of the bubbles representing Simpson's diversity index. The plot shows a strong positive correlation between Margalef's richness index and Shannon-Wiener index, while the size of the bubbles indicates a low value for Simpson's diversity index.

Despite its ecological significance, Bhosga Lake is facing various threats from human activities, such as washing clothes, bathing animals, and dumping domestic waste, which have led to the deterioration of water quality and eutrophication of the lake. The physicochemical profile and zooplankton diversity indicate that the conservation of faunal diversity and water quality in Bhosga Lake requires serious attention and reclamation efforts.

The violin plot (Figure 18) shows the distribution of four different diversity indices (Species richness, Shannon-Wiener index, Simpson's diversity index, and Evenness index) across four seasons (summer, Monsoon, winter, and spring) in Bhosga Lake. The x-axis of the plot represents the seasons, while the y-axis represents the values of the diversity indices. Each violin represents the distribution of values for a particular diversity index across the four seasons. The wider parts of the violin indicate a higher frequency of data points, while the narrower parts indicate a lower frequency of data points. From the plot, we can see that the species richness and Shannon-Wiener index have a relatively consistent distribution across all four seasons, with some variability in the Monsoon and spring seasons. The Simpson's diversity index shows a clear decrease from summer to winter and then an increase in spring. The Evenness index also shows a decrease from summer to winter and then an increase in spring.

Table 3 presents the diversity indices of zooplankton in Bhosga Lake across four different seasons, namely summer, monsoon, winter, and spring. Species richness (S), Shannon-Wiener index (H'), Simpson's diversity index (D), and evenness index (E) were used to evaluate the diversity of zooplankton. The table shows that the highest species richness was observed during the summer season, with 23 different species recorded. The Shannon-Wiener index, which takes into account both species richness and evenness, was highest during the summer season, indicating a more diverse community. The Simpson's diversity index, which indicates the probability that two randomly selected individuals from the same sample belong to the same species, was highest during the summer season, indicating a lower dominance of particular species. The evenness index, which measures the relative abundance of each species, was highest during the summer season, suggesting a more balanced distribution of species. The results suggest that the diversity of zooplankton in Bhosga Lake is highest during the summer season.

The table shows the range of various parameters including water temperature, pH, total dissolved solids (TDS), electrical conductivity, and dissolved oxygen (DO). The water temperature ranged from 22.2°C to 30.2°C, while pH varied from 7.6 to 8.8. The TDS ranged from 259 mg/L to 628 mg/L, while the electrical conductivity ranged from 476 µS/cm to 1134µS/cm. The concentration of DO was found to be lower than the standard limit in some months, indicating the eutrophication of the lake.

4. Conclusion

This study assessed the composition and diversity of zooplankton in Bhosga Lake, Kalaburagi District, and observed monthly variations and biodiversity indices of zooplankton. The study revealed the presence of 27 species of zooplankton, with Phylum Rotifers comprising the majority. The lake was found to be eutrophicated, and the conservation of faunal diversity and water quality requires serious attention and reclamation efforts. The results of this study have important implications for the management and conservation of Bhosga Lake and other similar aquatic ecosystems in the region.

References