BIOTROPIA Vol. 29 No. 1, 2022: 81 - 89 DOI: 10.11598/btb.2022.29.1.1662 81 NEUSTON DIVERSITY AND DENSITY AS BIOINDICATOR FOR WATER QUALITY IMAM SAFIR ALWAN NURZA*, JESSLYN GITTA VANIA, MUHAMMAD KHATAMI REYNALDI, ZAKI GUNAWAN RASYID AND RATNA KOMALA Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Negeri Jakarta, Jakarta 13220, Indonesia Received 9 September 2021 / Accepted 12 December 2021 ABSTRACT Lakes and waterfalls are freshwater ecosystems having important roles in ecology, tourism and economic aspects. Among living organisms existing in lakes and waterfalls is neuston. Neuston lives on the surface and below the surface of the waters. Neuston can be used as a bioindicator for water quality due to the neuston’s high level of sensitivity toward pollutants. The purpose of this study was to determine the density and diversity of neuston as a bioindicator for water quality in the lake and waterfall. The methods used were survey and observation. The study was carried out by using purposive sampling at two locations, namely the lake and waterfall of Situ Gunung, Sukabumi, with a sampling area of 1 x 1 m2. The samples obtained were put into bottles containing 70% alcohol to be identified in the laboratory. Environmental parameters measured were air and water temperature, water pH, water depth, turbidity, water flow velocity, dissolved oxygen, substrate and weather conditions. The results obtained indicated that the lake and waterfall of Situ Gunung, Sukabumi had highest neuston densities were shown by Gerris lacustris and Dineutus assimilis. The lowest neuston densities were shown by Metrobates hesperius, Gerris comatus, Aquarius remiges and Trepobates pictus. This study showed that the environmental parameters of the lake and waterfall of Situ Gunung, Sukabumi can still support the survival of the existing neustons. Keyword: density, diversity, neuston INTRODUCTION Freshwater ecosystems are divided into lentic/flooded freshwater ecosystems and lotic/flowing freshwater ecosystems. The examples of lentic freshwater ecosystems are lakes and swamps, while that of lotic freshwater ecosystems are waterfalls and rivers (Diantari et al. 2017; Ramadhan et al. 2016). The existence of the lake is considered important because it has an ecological, social, and economic roles for the surrounding environment (Postel & Carpenter 1997; Chen et al. 2020; Heino et al. 2021; Robert et al. 2020). The lake also acts as a habitat for several living organisms, such as neuston (Asnil et al. 2013; Ramadhan et al. 2016). According to Mulyono (2018), neuston floats on water (epineuston) or below the water surface (hyponeuston). Hyponeuston lives at a depth of about 0 - 10 cm (Rumnasih 2016). Neuston has a level of sensitivity to several contaminants so neuston can be used as a direct indicator for water contamination (Oktarina 2015) and as a bioindicator for water quality. The upper part of the waters is the most susceptible part to environmental exposure, which in turn will impact the neuston. Pollution often causes the formation of artificial stratification in lakes, where a body of water (hypolimnetic zone) is isolated. However, the hypolimnetic zone caused the contaminants trapped within the bottom of the waters and sediment masses (Sutrisno & Hamdani 2013; Williams 2001; Winton et al. 2019; Perron et al. 2014; Donyinah 2019). Waterfalls are a form of lotic freshwater ecosystem and are generally used as natural tourist objects (Siswantini & Mulyana 2017). The waterfall and lake in the Situ Gunung area, Sukabumi have an important role as one of *Corresponding author, email: imamnurza@gmail.com BIOTROPIA Vol. 29 No. 1, 2022 82 tourist attractions in Kadudampit District, Sukabumi, West Java Province, Indonesia (Soetopo 2011). Situ Gunung as a tourist object cannot be separated from tourists activities which will affect the surrounding environment, including the neuston community. Therefore, the purpose of this study was to determine environmental factors influencing the density and diversity of neuston as water quality bioindicator in the lake and waterfall in Situ Gunung, Sukabumi. MATERIALS AND METHODS The study was conducted in June 2021 at Situ Gunung, Gunung Gede Pangrango, Kadudampit District, Sukabumi. The methods used were survey and observation. The tools used were rope, wooden stick, measuring tape, thermometer, turbidimeter, DO meter, loop, field guide as an identification guide, stopwatch, plastic bottle, sample bottle, sample plastic, camera, net 1 x 1 m2, identification key book and stationery. The materials used were 70% alcohol, labeling paper and universal pH indicator paper (1 - 14). The study was conducted in two study locations, namely lake and waterfall in the shallowest part. Each location was represented by three observation stations based on differences in environmental conditions. Sampling was carried out three times at each station. Neuston collection was carried out at locations and stations that were purposively determined as a pick-up point sized 1 x 1 m2. Neuston samples were taken by using a 1 x 1 m2 net which was placed on the water surface. The net captured neustons which went through the filtration following the horizontal movement of the surface water in the lake and waterfall. Subsequently, the neustons sample was put into a bottle containing 70% alcohol. Samples were identified in the field and photographed for documentation. Environmental parameters measured were air and water temperature, water pH, water depth, water turbidity, water flow velocity, dissolved oxygen, substrate and weather conditions. The air temperature was measured using a calibrated air thermometer. Water temperature measurements were carried out using a DO meter. The pH of the water was measured using universal pH indicator paper (1 - 14). The water depth of the lake and waterfall was measured using a long wooden stick. The mark of the water depth was then measured by using a measuring tape. Water turbidity was measured by using a calibrated turbidity meter. Water flow velocity was measured by using floating method from the edge of the lake and waterfall. A rope was tied to a bottle and a 1-meter-long wooden stick. The bottle was floating at the water surface. The time taken from the moment the bottle was tied up to the wooden stick until the rope was stretched straight, was recorded by a stopwatch. The water flow velocity is expressed in m⁄s unit. The formula for calculating the water flow velocity is as follows: Flow Velocity = Rope Length (m) Time (s) Dissolved oxygen was measured three times using a DO meter. The substrate is the surface on which an organism lives. The substrate sample of the lake was taken using the Ekman Grab, while the substrate of the waterfall can be seen directly because the water depth is quite shallow. The substrate was determined by looking at its composition. The types of water substrates are sand, mud, rocks, lime, and others. Weather was determined by looking at the weather situation at the lake and waterfall environment. There are three kinds of weather conditions, namely sunny, cloudy, and rainy. Data analysis was carried out by determining the Simpson index using the formula as follows: 1. Density B = T x P A x S where: T = quadrant area (1 m2 = 10,000 cm2) P = area of the taking transect (m2) A = number of individual species S = number of taking transects 2. Diversity Ds = 1 – D  Ds = 1 –  Ni (ni – 1) N (N – 1) where: Ds = Simpson's diversity index Neuston Diversity and Density as Bioindicator for Water Quality – Imam Safir Alwan Nurza et al. 83 D = dominant index ni = number of individuals species N = total number of individuals RESULTS AND DISCUSSION There were six species of neuston found in the lake and waterfall of Situ Gunung. Four species were existed in the lake, namely Gerris lacustris, Metrobates hesperius, Gerris comatus, and Aquarius remigis (Fig. 1), while two species were found in the waterfall, namely Dineutus assimilis and Trepobates pictus (Fig. 2). Neuston species found in the lake and waterfall are different, depending on the habitat. Gerris lacustris and Gerris comatus are found in lakes due to their lentic habitat preferences. According to Ye et al. (2017), Gerris species inhabit several lentic habitats such as ponds, lakes and backwaters of streams. The habitat preference of Gerris lacustris is a high level of water depth, covered with vegetation, which is in agreement with a study conducted by Olosutean and Ilie (2013) who found that Gerris lacustris is correlated with water depth and have adaptation benefits from the presence of vegetation cover. The surface of the lakeside of Situ Gunung is covered with aquatic plants and the depth is relatively higher (58 - 93 cm) compared to the water depth of the waterfall (25 - 64 cm). In addition, Gerris comatus is a characteristic organism for lentic water. Gerris comatus is often found together with Gerris marginatus and Gerris buenoi (Damgaard et al. 2014; Pintar & William 2020). However, the last two species mentioned are not found in the lake. Figure 1 Neuston species found in the lake of Situ Gunung Notes: a. Gerris lacustris; b. Metrobates hesperius; c. Gerris comatus; d. Aquarius remigis Figure 2 Neuston species found in the waterfall of Situ Gunung Notes: a. Trepobates pictus; b) Dineutus assimilis a b dc a b BIOTROPIA Vol. 29 No. 1, 2022 84 Aquarius remigis were found in the lake of Situ Gunung, which fact is different from the statement of Ye et al. (2017) that Aquarius species are mostly confined to lotic habitats, such as water springs and rivers. Aquarius species can live in two different kinds of freshwater, both lentic and lotic. Aquarius species are semi-aquatic insects and opportunistic predators that live on the water surface of lakes, rivers, and the border between rivers and lentic habitats (Ditrich & Papáček 2016; Guterres et al. 2019). Metrobates hesperius were found in the lake because there are aquatic plants on the surface of the lakeside of Situ Gunung. Metrobates hesperius lays eggs on the leaves of the floating aquatic plants (Taylor 2009; Ikawa et al. 2012; Finet et al. 2018). The lake as a habitat supports the survival and distribution of these species. Dineutus assimilis and Trepobates pictus were found on the surface of a waterfall. Dineutus assimilis prefers both lotic and lentic waters, such as river surfaces, lakeshores and lakes (Gustafson & Miller 2015; MacLean 2013; Webster & DeMerchant 2012). Habitat preferences of Trepobates pictus were waters with slow water flow with eutrophic, muddy and rocky conditions in lotic waters (Naranjo et al. 2010; Taylor & McPherson 2006; Wooden 2019; Chordas 2017). The diversity index value (Ds) of neuston species obtained in the lake and waterfall for each station in Situ Gunung is presented in Table 1. Diversity index of 0.50 means low diversity, diversity index value of 0.50 to 0.75 means moderate diversity index, while diversity index of 0.75 to 1 means high diversity index (Nento et al. 2018). Table 1 Neuston diversity and total individuals in the lake and waterfall of Situ Gunung Location Station 1 Station 2 Station 3 Ds TI Ds TI Ds TI Lake 0.00 4 0.11 18 0.70 5 Waterfall 0.47 10 0.00 6 0.48 7 Notes: Ds = Diversity, TI = Total Individuals Table 1 shows that neuston diversity index value (Ds) varies among stations. The highest neuston diversity index in the lake occurred at station 3 with a value of 0.70 (moderate) with a total of 5 inviduals and 3 neuston species, namely Gerris lacustris, Gerris comatus and Aquarius remigis. Neuston diversity index value in the lake at station 2 was 0.11 (low) with a total of 18 individuals and 2 neuston species, namely Gerris lacustris and Metrobates hesperius. The lowest neuston diversity index in the lake occurred at station 1 with a value of 0.00 (low). In station 1, only one neuston species was found, namely Gerris lacustris with a total of 4 individuals. The highest neuston diversity index in the waterfall occurred at station 3 with a value of 0.48 (low), where 2 neuston species were found, namely Dineutus assimilis and Trepobates pictus with a total of 7 individuals. The lowest neuston diversity index in the waterfall occurred at station 2 with a value of 0.00 (low), where 1 neuston species was found, namely Dineutus assimilis with a total of 6 individuals. The neuston diversity index in the waterfall at station 1 was 0.47 (low) with a total of 10 individuals and 2 neuston species, namely Dineutus assimilis and Trepobates pictus. The different values of diversity index with total individuals obtained was due to dominant species in the lake and waterfall of Situ Gunung, namely Gerris lacustris and Dineutus assimilis. Table 2 Neuston density in the lake and waterfall of Situ Gunung Location Neutston species Neuston density (individu/m2) Lake Gerris lacustris 0.24 Metrobates hesperius 0.01 Gerris comatus 0.01 Aquarius remigis 0.01 Waterfall Dineutus assimilis 0.18 Trepobates pictus 0.05 The highest neuston density neuston in the lake was shown by Gerris lacustris with a value of 0.24 individu/m2. The three other neuston species, namely Metrobates hesperius, Gerris comatus, and Aquarius remigis showed the same density value of 0.01 individu/m2 (Table 2). On the lake surface of Situ Gunung at stations 1 to 3, there are aquatic plants. Gerris lacustris prefers to live on aquatic plants available on the lake surface of Situ Gunung. According to Yee (2016), Gerris lacustris spends most of its life on the surface of the water. In the lake of Situ Gunung there were two species of Gerris, namely Gerris lacustris and Gerris comatus. Gerris species can be found in almost all aquatic habitats from water springs to tropical seas (Yurtseven et al. 2016). At the waterfall of Situ Gunung, the Neuston Diversity and Density as Bioindicator for Water Quality – Imam Safir Alwan Nurza et al. 85 highest neuston density was shown by Dineutus assimilis with a value of 0.18 individu/m2 and Trepobates pictus with a value of 0.05 individu/m2. The common aquatic insects found in Indonesian freshwater are of the Order Odonata, Coleoptera, Trichoptera, Hemiptera, Ephemeroptera, Plecoptera and Lepidoptera (Mahajoeno et al. 2001; Candra et al. 2014). In the lake and waterfall of Situ Gunung, we found Orders Hemiptera and Coleoptera. Every species found in the lake of Situ Gunung belongs to Gerridae family. According to Dwitawati et al. (2015), Gerridae family is classified as having a low tolerance for pollutants. Meanwhile, Gerris lacustris, Gerris comatus, Metrobates hesperius and Aquarius remigis belong to the Order Hemiptera. Hemiptera insects often move rather than being settled in an unwanted location (Mercer et al. 2017; Peterson et al. 2017; Wooden 2019). The predominant presence of Hemiptera insects indicates that the lake is relatively less polluted (Majumder 2013). The pollution that contaminates the lake of Situ Gunung is thought to come from household wastes and human recreational activities. Aquatic insects are a good bioindicator for detecting pollution. Aquatic insects are also useful for fish food and biocontrol agents (Dalal & Gupta 2016; Ito et al. 2017). Therefore, long-term monitoring of aquatic insects is needed to evaluate water quality. Table 3 shows that the pH values in the lake of Situ Gunung for all stations are relatively constant, namely 6 (acid). The standard pH for clean water quality ranges from 6.5 to 9.0. The pH value in the lake of Situ Gunung which is below the clean water standard is suspected to have been polluted by household wastes due to the closeness with the mainland, hence acidic pH value. The acidic pH value is not within the suitable environment for the neuston's life. Neuston can develop well in the pH range of 6.8-8.5 (Gundo 2010; Pratami et al. 2018). pH affects dissolved oxygen levels. The lowest dissolved oxygen level for the lake of Situ Gunung location was found at station 2, which was 3.28 mg/L. The acidic pH causes an increase in toxic substances in the water and decreases dissolved oxygen levels (Pratami et al. 2018). Dissolved oxygen plays an important role in the respiration process of most aquatic organisms (Hariyani et al. 2017; Pratami et al. 2018). The average of dissolved oxygen level in the lake of Situ Gunung was 3.62 mg/L. Dissolved oxygen levels also indicate the level of pollution waters. Dissolved oxygen levels below 5 ppm mean low pollution levels (Hariyani et al. 2017). The low dissolved oxygen level shown in the lake of Situ Gunung indicated that the pollution level was low enabling neuston organisms such as water insects to obtain the needed oxygen for the respiration process. The lake of Situ Gunung showed the highest water turbidity value at station 1, which was 11.97 NTU. The high value of water turbidity is presumably caused by the existing fishing activities by humans and aquatic plants on the lake surface at station 1. Penetration of sunlight into the lake waters can be hindered by the high value of water turbidity (Pratami et al. 2018). The lowest value of water turbidity was shown at station 2, which was 4.44 NTU. The different value of water turbidity at station 2 compared to the other two stations is presumably caused by the utilization of station 2, which function is docking place for boats. Also, only a few of aquatic plants were existing in station 2. The measurement of environmental parameters of the waterfall of Situ Gunung showed air and water temperatures of 20.7 oC and 17.9 °C, respectively, indicating a cold-water habitat for insects (Table 4). In the environment of the lake of Situ Gunung, the air and water temperatures of 29 oC and 28 °C, respectively, indicating a warm-habitat for insects (Table 3). According to Mujiono et al. (2019), the higher the place is, the colder the temperature. The average of water pH of the waterfall of Situ Gunung is 6 (acidic) with average of Dissolved Oxygen value of 7.77 mg/L. Dissolved oxygen levels are high in the waterfall because the waterfall is located on a hill surrounded by natural forests and has low pollution levels. Meanwhile, the lake water is murky indicating water pollution that affects dissolved oxygen levels. In addition, the murky water can cause the increase of oxygen uptake from the air into the water causing the increase of dissolved oxygen in the water (Diantari et al. 2017; Mujiono et al. 2019; Irby et al. 2015). BIOTROPIA Vol. 29 No. 1, 2022 86 Table 3 Environmental parameters obtained from the lake of Situ Gunung Environmental parameter Station Mean 1 2 3 Water pH 6 6 6 6 Air temperature (oC) 29 29 29 29 Water temperature (oC) 28.03 27.93 27.93 27.97 Water depth (cm) 58 71 93 74 Water turbidity (NTU) 11.97 4.44 11.85 9.42 Water flow velocity (m/s) 0.009 0.022 0.0085 0.013 Dissolved Oxygen (mg/L) 4.24 3.28 3.33 3.62 Substrate Mud and rocky Mud and rocky Mud and rocky Weather Cloudy and rainy Cloudy and rainy Cloudy and rainy Table 4 Environmental parameters obtained from the waterfall of Situ Gunung Environment Station Mean 1 2 3 Water pH 6 6 6 6 Air temperature (oC) 20.8 20.8 20.5 20.7 Water temperature (oC) 17.9 17.9 17.9 17.9 Water depth (cm) 25 53.33 64.33 47.56 Water turbidity (NTU) 0.41 0.46 0.51 0.46 Water flow velocity (m/s) 0.49 0.58 0.13 0.40 Dissolved Oxygen (mg/L) 7.54 7.71 8.05 7.77 Substrate Rocky Rocky Rocky Weather Sunny Sunny Sunny The water flow of the stations at waterfall of Situ Gunung showed an average of water flow velocity of 0.40 m/s which affects the presence of swimming-type aquatic insects. Due to the high value of water flow velocity and the presence of rocky substrate, the water insects hide behind rocks (Leba et al. 2013). According to Diantari et al. (2017), the rocky substrate can affect the water flow velocity in a stream. The lake water's flow velocity of 0.01 m/s causes the lake to be predominated by neustons with floating ability. The average water turbidity of the waterfall of Situ Gunung was 0.46 NTU with an average water depth of 47.56 cm. Meanwhile, the lake showed an average turbidity of 9.42 NTU with an average water depth of 74 cm (Table 3). Our study showed that sunlight easily penetrated the waterfall. However, the murky lake water hindered the sunlight penetration into the lake. Small value of water turbidity can support filter- feeder organisms and affect the activities of the existing Orders Hemiptera and Coleoptera (Ebenebe et al. 2016; Marpaung et al. 2014). CONCLUSION Six neuston species were identified in Situ Gunung, namely four species in the lake of Situ Gunung and two species in the waterfalls of Situ Gunung. The four neuston species in the lake namely Gerris lacustris, Metrobates hesperius, Gerris comatus and Aquarius remigis, while the two neuston species waterfalls namely Dineutus assimilis and Trepobates pictus. The highest neuston densities in the lake and waterfalls were represented by Gerris lacustris and Dineutus assimilis, respectively. Neuston diversity in the lake and waterfalls of Situ Gunung was low. Environmental parameters of the lake and waterfalls of Situ Gunung were still in the normal range, except low water pH indicating polluted waters environment. Therefore, long- term monitoring at the waters of Situ Gunung is needed for evaluating water quality parameters that support the life of aquatic organisms. 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