PHYTOPLANKTON DIVERSITY AS A BIOINDICATOR FOR WATER QUALITY OF SIWAK BAY, SPECIFIC ECONOMIC ZONE (SEZ) MANDALIKA CENTRAL LOMBOK

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INTRODUCTION
West Nusa Tenggara (NTB) Province has a sea area of 29,159.04km 2, and the length of the coastline is around 2,333 km [1].The vastness of this marine water area makes NTB one area with a variety of water natural resource (SDA) potential.One area that has marine and coastal potential is Central Lombok, especially the Mandalika Special Economic Zone (SEZ).
SEZ Mandalika is one of the tourist attractions in the south of Lombok Island.The Mandalika SEZ was approved as a tourism SEZ through PP No. 52 of 2014 [2].SEZ Mandalika is a potential tourism industry in NTB Province.This is an attraction for companies developing the tourism industry [3].One of the tourism sectors that is currently receiving high attention is the international MotoGP circuit.The construction of this circuit is an attraction for domestic and foreign tourists.The increase in tourism activities in coastal areas impacts the amount of organic and inorganic pollutants in water bodies and other potential problems that can become coastal environmental problems.
Phytoplankton are microscopic organisms that are autotrophic or capable of producing food through photosynthesis [4].Phytoplankton acts as primary producers, and it is estimated that 95% of primary production in the sea comes from phytoplankton [5].Phytoplankton are the first organisms to be disturbed if pollutants enter the water.This is because phytoplankton utilize these pollutants directly.Thus, changes in waters are caused by changes in the phytoplankton community structure [6].Therefore, phytoplankton can be used as a bioindicator in evaluating the level of pollution in waters.
Phytoplankton, as a bioindicator of water quality, has been studied by many researchers from the perspective of diversity, abundance, and dominance to determine the condition of a body of water.Japa research et al. said that the waters of the Mandalika SEZ have a moderate microalgae species diversity index of 3.145, with the dominant species being Cahaetoceros.Based on the species diversity index results, the water quality status of the Mandalika SEZ is not polluted [7].Research has also been carried out at Klui Beach by Hadi et al., who said that Klui coastal waters were classified as unpolluted and found as many as 48 species of phytoplankton from the Bacillariophyceae class with an average species abundance of 298.09 ind/L [8].It was also reported that the waters of the Sekotong gold processing area were moderately to heavily polluted and had 41 phytoplankton species with a diversity ranging from 2,814 to 2,817 [9].
Siwak Bay is one of the locations still in the Mandalika SEZ, Central Lombok.This area has residents' houses and local community activities such as collecting seaweed, animal husbandry, agriculture, and madak activities when the water recedes.The location of Siwak Bay, which is still in the Mandalika SEZ, means that this area is indirectly affected by the development and management of Mandalika, which can result in a decline in environmental quality.Apart from that, reports regarding the condition of the waters of Siwak Bay using phytoplankton as a bioindicator have never been carried out.Therefore, it is necessary to carry out this research to determine the status of the waters of Siwak Bay using phytoplankton as a bioindicator.

RESEARCH METHOD Time and Place of Research
This research was carried out in March 2023 in Siwak Bay, Central Lombok.Phytoplankton samples were observed and identified at the Biology Laboratory, Faculty of Mathematics and Natural Sciences, Mataram University.
This type of research is descriptiveexploratory, describing in detail the condition or phenomenon of phytoplankton in Siwak Bay.The sampling point is determined by the technique of purposive sampling, which is based on consideration of environmental conditions, consisting of 9 points (Figure 1).The coordinates of each sampling point are listed below in Table 1.

Laboratory Sampling and Observations
Phytoplankton samples were taken at each sampling point at 08.00-13.00WITA, using a plankton net with a mesh size of 20 µm.Seawater samples were preserved using formalin with a preservation concentration of 4%.Physical-chemical parameter measurements were carried out at each sampling station; the parameters measured were temperature, pH, salinity, current speed, and nitrate.
Phytoplankton observations were carried out using an electric binocular microscope (Zeiss Primo Star) with magnifications of 10x10 and 40x10.The results of observations of phytoplankton observed in a microscope were photographed using a camera cell phone 48 megapixels (MP).The phytoplankton species obtained were then identified using booksThe Marine and Freshwater Plankton, Algae Second Edition, Illustrations of The Marine Plankton of Japan 3rd Edition, The Freshwater Algae of United States of America [10][11][12][13]

Data analysis
The equations used in calculating observational data in this study include species abundance, species diversity index (H'), and species dominance index (C).The individual abundance of each phytoplankton species was calculated using the equation [14].The phytoplankton species diversity index was calculated using the Shannon-Wiener index [15].Criteria for assessing the phytoplankton species diversity index are listed in Table 2 [16].The phytoplankton species dominance index can be calculated using the Simpson equation [15].Criteria for assessing the dominance index of phytoplankton species are listed in Table 3 [16].Criteria for assessing the level of pollution of a body of water based on the phytoplankton species diversity index are listed in Table 4[17].

RESULTS AND DISCUSSION Phytoplankton Composition
Based on the results of research carried out at three stations divided into nine sampling points in the waters of Siwak Bay, it is known that the composition of phytoplankton includes seven classes, 59 genera and 127 species of phytoplankton, namely class  In general, based on the results found, species from the Bacillariophyceae class were most commonly found in all research stations (Figure 2).The research conducted by Purwaningtyas in Teluk Gerupuk obtained species from the Bacillariophyceae class that are the most common [18].Class Bacillariophyceae is also found in the waters of Sungai Jangkok in as many as 84 species [19].This shows that the Bacillariophyceae class has a wide distribution in both fresh and marine water.Phytoplankton from the class Bacillariophyceae are often found in aquatic environments due to their excellent adaptability, tolerance to extreme temperatures, cosmopolitan nature, and high reproductive capacity [20].Phytoplankton species in the waters of Teluk Siwak that come from the Bacillariophyceae class are listed in (Figure 3).
The phytoplankton found in the waters of Siwak Bay are very diverse and have a very potential role in the sea.Genus Amphora of the Bacillariophyceae class, most commonly found in the waters of Siwak Bay, namely 11 species.Genus Amphora is useful as a natural food for shellfish and shrimp larvae because it contains high protein, fat, and carbohydrates [21].It also has an essential role in water, namely as a primary producer.Apart from being a primary producer, Nitzschia also serves as natural food for the larvae of marine organisms such as crustacea, bivalves, and fish [22].Besides that, Nitzschia can be used as a basic material for developing biodiesel because organisms produce potential lipids [23].The abundance of phytoplankton in the waters of Siwak Bay is 1031.48ind/L and varies from one station to another.The highest abundance of phytoplankton was at station III, namely 1720 ind/L, followed by station II, namely 745.56 ind/L, while the lowest abundance was at station I, namely 711,111 ind/L.Environmental conditions and activities can influence differences in abundance values for each station in the waters of Siwak Bay.A comparison of abundance data for each station is listed belowfigure 4. The physical and chemical parameters of Siwak Bay waters are listed in Table 6  The highest species abundance was found at station III at 1720 ind/L.The high phytoplankton abundance value at this station can be influenced by physical and chemical water parameters such as temperature, salinity and nitrate.This is thought to be because the location of observation station III is close to residential areas.The water temperature at station III was found to be 29.8O C, where this value is higher compared to other stations.In accordance with Puspitasari's opinion, high and low temperatures can influence the abundance of phytoplankton [24].Campbell confirmed that increasing temperature can cause an increase in plankton growth rates [25].The abundance of phytoplankton is also influenced by salinity, where salinity in the range of 30-35 is the optimum value for the survival of phytoplankton [26].The salinity measured in the waters of Siwak Bay is 30-32 ppt.Apart from that, nitrate is one of the factors that influences the abundance of phytoplankton.The nitrate value at station III is higher compared to stations I and II, namely 0.1 mg/L (Table 5).This was due to the fact that at station III there were grass cultivation activities and there were landslides that entered the water body during sampling.
The lowest abundance was found at station I at 711.11 ind/L.The low abundance value obtained is thought to be due to the lack of nitrate concentration at this station because, at the time of sampling, there was no water resulting from community activities, which usually enters the waters of Siwak Bay.Water entering the coast will carry waste in the form of anthropogenic activities (nitrate, nitrite, and phosphate), where the high level of incoming waste greatly influences the high and low values of nitrate [24].
The abundance at station II was found to be 751.11,which is lower than the abundance value obtained at station III.Environmental factors influence this.Current is something that influences the abundance value obtained at station II, which is lower than at station III; the current speed value obtained is 0.9 m/s.In line with the argumentation from Roioto et al.., the low abundance of phytoplankton can be influenced by phytoplankton carried along with the movement of water due to fairly strong current movements [27].
Genus Trichodesmium is the genus that has the highest abundance in the waters of Siwak Bay.Environmental factors can influence the abundance of Trichodesmium, namely the resistance of these organisms to high temperatures [28].The temperature in the waters of Siwak Bay ranges from 28.8-29.8O C. This temperature range can support the development of Trichodesmium.This is in line with Devassy's opinion that waters have temperatures ranging between 27-32℃, which is the best temperature for the growth Trichodesmium [29].In addition, the abundance of the genus Trichodesmium is also due to its ability to bind nitrogen from the air in marine waters that have low nitrate content [30].The nitrate content measured in the waters of Siwak Bay is 0.05-0.1 mg/L, where nitrate levels in the range of 0-1 mg/L include waters with low nutrient levels (oligotrophic) [31].This is what causes this genus to easily reproduce its individuals in a short time [32].Trichodesmium, which is a member of the phylum Cyanophyta, is found in abundance because Trichodesmium has high adaptability due to its unique personality and abilities, which make this organism different from aquatic organisms in general.Besides that, Trichodesmium can also reproduce in a very short time to double the number [29].

Diversity and Dominance of Phytoplankton Species
There are 127 phytoplankton found in the waters of Siwak Bay, Central Lombok, which fall into seven classes, namely Bacillariophyceae, Cyanophyceae, Dinophyceae, Chlorophyceae, Coscinodiscophyceae, Ulvophyceae, and Florideophyceae.The species diversity index for each station is presented in Table 5.The diversity index shows the number of species that are able to adapt to the environment occupied by an organism [14].An area's ecosystem is said to be balanced and can be characterized by a high species diversity index; on the other hand, aquatic ecosystems that are unstable or do not support biota life have low diversity values.The phytoplankton species diversity index in the waters of Siwak Bay is 3.353 and differs between stations (Figure 4).According to Fachrul, the species diversity index with a value of H'>3 is included in the high category [16].
The physical and chemical factors of a body of water influence the level of phytoplankton diversity.Phytoplankton diversity in Siwak Bay is influenced by environmental parameters that support phytoplankton life, for example, pH.The pH value of Siwak Bay waters ranges from 7.8-8.The pH value range of 6-9 is the optimum value for phytoplankton growth, and this is because the pH of the water affects minerals from the decomposition of organic matter.
The phytoplankton dominance index in Siwak Bay waters ranges from 0.06-0.11.The values obtained indicate that there are no dominant species in the waters of Siwak Bay.This follows Fachrul's opinion that a dominance index value close to 0 indicates no dominant species.Conversely, if the dominance index value is close to 1, it indicates a dominating species in the waters [16].Thus, it can be concluded that in the waters of Siwak Bay, there is no dominance.The phytoplankton samples that have been analyzed also show an important value index (INP) for phytoplankton, namely 200.0605,where the highest important value is obtained from the genus Trichodesmium amounting to 79,678.High INP of the genus Trichodesmium This is because Trichodesmium is often found in oligotrophic waters and waters that have a temperature range between 20-34℃ [33].The waters of Siwak Bay are oligotrophic and have a temperature range of 28.8-29.8O C. It supports the growth of Trichodesmium in the waters of Siwak Bay.
Based on the research results, the phytoplankton diversity index value in the waters of Siwak Bay was 3.33 (high category).Therefore, it can be said that the water quality of Siwak Bay, Central Lombok, based on the phytoplankton species diversity index as a bioindicator, is in the non-polluted category.This is in line with Barus' opinion, namely that if a body of water has a species diversity index greater than 2, it indicates that the water is not polluted [17].

CONCLUSION
The results of this research concluded that there were 131 phytoplankton species in the waters of Siwak Bay with a high species diversity index (H'= 3.353), and an abundance of phytoplankton species of 1031.48 ind/L.The highest abundance belongs to the genus Trichodesmium, with an abundance of 408.51 ind/L.The water quality of Siwak Bay based on the phytoplankton species diversity index shows that the water condition is good and not polluted.

Figure 2 .
Figure 2. Percentage of Phytoplankton Presence in Siwak Bay Waters

Table 2 .
Species Diversity Index Value Criteria

Table 3 .
Species Dominance Index Value Criteria

Table 4 .
Aquatic Status Criteria Based on Diversity Index .

Table 5 .
Physical Chemical Parameters of Siwak Bay Waters