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The diversity of plankton as bioindicators in Kakap River Estuary, West Kalimantan

DOI: 10.13170/depik.10.2.21303 Kakap River Estuary plays an essential role in the life organisms, but it is vulnerable to environmental changes and pollution caused by human activities. This study aims to assess the presence of plankton species, their abundance and diversity as aquatic ecological bio-indicators in Kakap River Estuary. Plankton and water samples were taken for three months, with a frequency of one sample per month, viz. in March, April and June 2020 from four sampling stations in Kakap River Estuary, West Kalimantan. A total of 34 species of plankton were observed from all sampling sites, and identified to belong to 18 classes. Chlorophyceae had the highest relative abundance among the phytoplanktons (40.10%), followed by Bacillariophyceae (21.86%) and Cyanophyceae (19.28%). Oscillatoria sp. and Hydrodictyon sp. were the most dominant phytoplankton species. There were 8 classes of zooplankton identified from all sampling stations throughout the research period. Hexanauplia had the highest relative abundance among the zooplanktons (36.56%) followed by Euglenophyceae (24.37%). The plankton diversity index (H ′) values ranged between 2.33 -3.11. The plankton evenness index value ranged from 0.79 to 0.89 which indicates high plankton evenness at all samping stations, and this is supported by a low dominance index value at all stations ranging from 0.06-0.16. Station 1 had high Shannon-Wienner diversity index score, while for station 2, 3, 4, their scores were in the moderate level. Overall. the diversity index of the plankton from all sampling sites indicated that the quality of the water had no pollution to light pollution level.


Introduction
Human activities affect the quality of water bodies including lakes, seas, rivers and estuaries (El-Zeiny and El Kafrawi 2017;Fadillah et al., 2017). The estuary is a transitional zone between land water bodies (rivers, streams) and the ocean where the mixing of freshwater and saltwater occurs, or a, giving this area unique characteristics (Hakiki et al., 2017). Estuaries are also a productive area, due to the increased input of organic matter from the land and upstream rivers. Estuaries also play an important role in the life of aquatic organisms, namely as a source of nutrients, as habitat and shelter for various biota, areas of food source, spawning grounds, and also as nursery ground for a number of shrimp and migratory fish species. Furthermore, estuaries are also a habitat for plankton and nekton. Estuaries are very dynamic areas that are vulnerable to environmental changes and pollution caused by human activities, including through the disposal of waste which can come from domestic area, industrial, and other public places (Suoth and Nazir, 2016). This condition is also present in the Kakap River Estuary.
The estuary of Kakap River is located in Sungai Kakap District, Kubu Raya Regency, West Kalimantan. In this area, there are not only domestic activities going on. Due to the existence of a fishing port, there are also capture fisheries activities and a fish processing industry. Currently, the Kakap River Estuary seems to have been polluted by domestic waste, market waste, and fish waste. This condition can cause disruption of the ecosystem which then affects the life of the biota living in it, including plankton.
Generally, water quality can be observed and measured by a variety of physical, chemical and biological methods. Examples of the biological Depik Jurnal Ilmu-Ilmu Perairan, Pesisir dan Perikanan Volume 10, Number 2, Page 174-179 Soetignya et al. (2021) methods used to study water quality includes the collection, counting and identification of aquatic organisms, such as plankton. Plankton is a group of aquatic biota aquatic, which includes both phytoplankton and zooplankton, whose movements are influenced by currents (Kutama et al., 2014). This biota can provide information on water condition, one of which is as an indicator of pollution (Igwe et al., 2019;Krupa et al., 2020). Research on the use of phytoplankton as a bioindicator has been conducted by Fatmayanti et al., (2019), Yusuf (2020), and Zhu et al. (2021), while research on the use of zooplankton as a bioindicator has been conducted by Neto et al. (2014). This study aims to assess the presence of plankton species, their abundance and diversity as aquatic ecological bio-indicators in Kakap River Estuary.

Materials and Methods Location and time of research
The research was conducted monthly for three months, viz. in March, April and June 2020 at the Kakap River Estuary, Kubu Raya Regency, West Kalimantan ( Figure 1). The tools and materials used in this study were as follows: plankton net (mesh size 25µm), dropper pipette, label, flacon bottle, camera, Secchi disk, thermometer, pH indicator, refractometer, ruler, distilled water, DO meter, 1liter water sample bottle, formalin 4%, microscope, Sedgwick Rafter Counting Cell (SRC), and plankton identification books i.e., Davis (1995) and Mizuno (1979).
The data was collected using purposive sampling method, at four stations which were divided based on the characteristics of the potential waste load estimation. Station 1 was located at the estuary with the characteristics of a densely populated location with suspected domestic waste from human activities, station 2 was located in the fish auction market section with the characteristics of a fishing boat port and ship waste, station 3 was located close to the sea in Pekong which is an area for ship anchoring and fish processing. Station 4 was located near the mangroves with the characteristic of the absence of human population. Data collection was divided into 2 categories i.e., primary data and secondary data.
Primary data consists of data on plankton types as well as their abundance. Plankton data collection was carried out by filtering 100 L of water samples using plankton net. The filtered sample was then preserved using 4% formaldehyde and then analyzed in the laboratory. The physical-chemical water analysis method used in Kakap River Estuary is referred to APHA 2012 (Table 1). The physical parameters analyzed included temperature, water color, water odor, transparency, depth, current, Total Dissolved Solid (TDS) and Total Suspended Solid (TSS) while chemical parameters included pH, (Dissolved Oxygen (DO), Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), salinity, alkalinity, and hardness.
Secondary data that was collected include tidal data that was obtained from the Pontianak Maritime Meteorological, Climatological, and Geophysical Agency. In addition, data on the population and education level were collected from Sungai Kakap Village. Interviews were also conducted with several fisherman and people in the village.

Data analysis Plankton abundance
The abundance of plankton can be calculated using an SRC using cell/m 3 or ind/m 3 units. The formula used was based on Baird et al. (2017): Depik Jurnal Ilmu-Ilmu Perairan, Pesisir dan Perikanan Volume 10, Number 2, Page 174-179 Soetignya et al. (2021) Description: N = Plankton abundance (cell/m 3 or ind/m 3 ); n = number of observed plankton; Vd = volume of filtered water sample (m3); Vt = volume of water in the sample bottle (ml); Vsrc = volume of water in the SRC (ml); Asrc = SRC's area of view (1000 mm 2 ); Aa = area of view (mm 2 ).

Shannon-Wiener diversity index (H ')
The Shannon Wiener diversity index was calculated on the basis of the number of taxa and individual abundance of organisms present in the sample.
Description: H′ = Shannon-Wiener diversity index; Pi = ni/N; ni = number of individual species-i th ; N = total number of individuals; H′< 1 = the biota community is unstable; 1<H′<3 = The stability of the biota community is moderate; H′> 3 = the stability of the biota community is in prime condition (stable).

Evenness index (E)
According to Michael (1994), this index shows whether or not the distribution pattern of living organisms is evenly distributed. If the index value is relatively high, each type of living organisms present in the waters are evenly distributed even. Evenness index was determined using the following formula:

E = H′ Hmax
Description: E = Evenness index; H′ = Shannon-Wiener diversity index; H max = Ln S (S is the number of genera); E = 0-0.5, distribution between species is not even, meaning that the number of individuals of each species is very different. E =0.6-1, The distribution between species is relatively even or the number of individuals of each species is relatively the same

Simpson dominance index (C)
The Simpson dominance index is used to determine the dominance of certain species in the waters with the following formula (Michael, 1994): Description: C = Simpson dominance index; ni = number of individual species-i th ; N = total number of individuals.
The dominance index values ranged from 0-1. A value close to zero indicates that there is no dominant genus in the community. Otherwise, if a value is close to 1 indicate the dominant genus.

Results
This section reports the total composition, the relative abundance and the community index of the plankton from the four sampling sites through the research period. The total number of plankton species found at the sampling location was 34 species belonging to 18 classes, which consisted of 10 phytoplankton and 8 zooplankton classes. Station 1 had the highest number of species for plankton, meanwhile the lowest number of species was found at station 4 ( Figure 2).
The highest abundance was recorded at station 1 and the lowest abundance was at station 4. The abundance of plankton for stations 1,2, 3, and 4were 92,000 cells/m 3 plankton; 47750 cells/m 3 plankton; 36,000 cells/m 3 plankton and 23,750 cells/m 3 plankton respectively (Figure 3).  In this study, a total of 10 phytoplankton classes were recorded from all sampling stations. Chlorophyceae had the highest relative abundance among the phytoplanktons (40.10%), followed by Bacillariophyceae (21.86%) and Cyanophyceae (19.28%) (Figure 4) There were 8 zooplankton classes sampled from all sampling stations throughout the research period. Hexanauplia had the highest relative abundance of the zooplankton (36.56%) followed by Euglenophyceae (24.37%) ( Figure 5).   Figure 6). Station 1 had a high level of Shannon-Wienner diversity index, which means the plankton community was stable, while for station 2, 3, and 4 it was at the moderate level. Referring to Zhu et al. (2021), the plankton diversity index at station 1 which scored higher than 3, indicates that the water was not polluted, while other stations that have a diversity index between 2 and 3 indicates light pollution levels. The plankton evenness index value ranges from 0.79 to 0.89 which indicates high level of plankton distribution evenness at all stations, and this is supported by a low dominance index value at all stations ranging from 0.06-0.16.

Discussion
Generally, water quality is detected and determined using a variety of physical, chemical and biological methods. Physico-chemical observation results of Kakap River estuary showed that the waters are still suitable with standard quality value category of class 3 (fisheries purposes) based on PP RI No. 22 (2021). Referring to Lee (1978), the Kakap River had a light to moderate pollution level. Analysis of plankton diversity had been conducted to support and complement the interpretation of the results obtained from physico-chemical analysis. As aquatic organisms, plankton has many advantages for biological models, namely being able to indicate the level of ecological instability and pollution levels.
The plankton diversity in Kakap River estuary varied between all sampling stations. This is influenced by the conditions of the aquatic environment and land use. Station 1 had a high number of species, abundance and diversity level of plankton which indicates that the waters have a good ecological status. DO at station 1 was higher than the other stations, and there was also nutrient input from the discharge of organic matter into the waters, as a result the diversity of species and abundance of plankton at this location is high. The presence of these nutrients affected the growth of plankton in the waters (Mahlil et al., 2018). Runoff from settlements contains a lot of nutrients that enter the water body and are used for plankton growth. Even though BOD value is quite high at this station, it has not disturbed the ecological condition and still suitable with the quality standard value based on PP RI No. 22 (2021).
The use of species diversity indices (the Shannon-Wiener index) showed that with the increasing pollution, the diversity of communities decreases (Vallina et al., 2017). Based on the Shannon-Wiener diversity index, the plankton communities at stations 2, 3 and 4 were classified as moderate, which indicates the degree of light pollution, referring to Zhu et al. (2021). Stations 2 and 3, which are located as fishing ports and produce ship waste, may affect the presence of plankton at that location. Boat waste such as oil spill will affect the water quality needed for plankton growth, as seen from the descriptive observations of the two stations having a lower DO range when compared to stations 1 and 4. While station 4 is located near the mangroves with the characteristic absence of human population. This caused the low number of plankton species at station 4 due to the low organic matter presence at this station (Table 2). Low transparency will inhibit phytoplankton to carry out photosynthesis (Avila-Alonso et al., 2016). Conversely, high transparency increases the solar radiation intensity that can be absorbed by phytoplankton. An increase of solar radiation intensity has positive effect on photosynthesis and other metabolic activities with a subsequent increase in phytoplankton population abundance (Tanimu et al., 2011).
According to Kutama et al. (2014), the composition and abundance of plankton in a water body clearly indicates the health status of the water body. Planktons show different responses to different environmental conditions. In the present study, the three dominant phytoplankton classes are Chloropyceae, Bacillariophyceae and Cyanophyceae. These three phytoplankton classes were also found to dominate in several studies (Gulecal and Temel, 2014;Cao et al., 2016;Zhu et al., 2021). Chlorophyceae class (40.10%) was found to be the most abundant compared to others. This is because green algae (Chlorophyceae) is the most diverse algae class with a high reproductive abilities compared to those found in any other algal divisions (Adesalu, 2016). Bacillariophyceae (diatoms) tend to dominate in fast-flowing waters and as benthic algae. This is related to their ability to withstand the high current velocity and water-level fluctuations (Trabert et al. 2020). The dominance of diatoms could be owing to the fact that they can tolerate widely dynamic hydrographical conditions. According Dembowska et al. (2018), the predominance of diatoms population is an indication of eutrophic state of waters. Among the diatoms recorded in Kakap River estuary, Navicula sp. is pollution indicator belonging to Bacillariophyceae as pointed out by Palmer (1969), similarly with Cyanophyceae which is one of the algae classes that are found in abundance in various habitats (Albrecht et al., 2017). At stations 1 and 4, the most dominant phytoplankton species is Oscillatoria. This may be related to the DO content, where stations 1 and 4 have a higher DO range than stations 2 and 3. According to Zhu et al. (2021), beside NO2-N, Oscillatoria is positively correlated with DO. Oscilltoria sp. is also a pollution indicator species belonging to Chlorophyceae as described by Palmer (1980). Meanwhile, the most dominant phytoplankton species at stations 2 and 3 is Hydrodiction sp. Occurrence reports of Hydrodiction are often associated to human-caused environmental changes, and their distribution can also be affected by humans (Peres et al., 2016).
The Hexanauplia class is the most abundant zooplankton found in the Kakap River estuary, this class has a high adaptability and can survive in various water conditions (Antuke et al., 2019). The Depik Jurnal Ilmu-Ilmu Perairan, Pesisir dan Perikanan Volume 10, Number 2, Page 174-179 Soetignya et al. (2021) Euglenophyceae class is also a group whose frequency is often found to be quite high in fresh, brackish and marine waters (Bicudo and Menezes, 2016).

Conclusion
The diversity of plankton is a very important tool to be used as indicator of water quality in the Kakap River estuary. There were 34 species of plankton belonging to 18 classes observed from all sampling sites. The plankton diversity index (H′) values ranged between 2.33 -3.11. The plankton evenness index value ranges from 0.79 to 0.89 which indicates high levels of plankton evenness at all stations and is supported by a low dominance index value at all stations ranging from 0.06-0.16. Station 1 had high score for the Shannon-Wiener diversity index, while stations 2, 3, and 4 had moderate scores. Overall, the diversity index of the plankton from all sampling sites confirms that water quality in Kakap River estuary ranged from no pollution to light pollution level.