Current status of environmental water quality of Kappaphycus alvarezii seaweed cultivation in the Seribu Islands, Indonesia and the concept of sustainable development by using a System Dynamic Model approach

The aim of this research is to analyze the current status of water quality in seaweed cultivation environments related to the decline in seaweed production. Field research was conducted in the Seribu Islands Regency, DKI Jakarta, during April and May 2023. The analysis of environmental factors encompassed physical, chemical, and biological parameters at 12 designated sampling points. The results of the analysis of water quality parameters generally meet the requirements, except for oil and grease at 7-51 mg/L and nitrate at 1.60-6.3 mg/L, both of which exceed the quality standards for biota. Plankton analysis shows the total abundance of plankton reaches 36 to 9,070 ind/L. Evaluation of the suitability class shows that the waters are in class S (Suitable). The Pollution Index value ranges from 6.51 to 8.05, indicating a fairly polluted status. The high levels of oil and grease, nitrate, and the presence of index pollutants have a significant influence on the decline in seaweed production in the Seribu Islands Regency. The preparation of improvement strategies can be conducted using a System Dynamics Model approach, involving the creation of comprehensive Causal Loop Diagrams. This process considers four key factors: environmental water quality, human resources, technology, and seaweed.


Introduction
Kappaphycus alvarezii is one of the important types of seaweed in Indonesia, known for its high economic value as a raw material for the domestic industry and as an export commodity.However, production has steadily declined over the last 5 years, dropping from 11,050,031 tons in 2016 to 9,059,114 tons in 2021 [1].Many factors influence seaweed cultivation activities, including environmental, technological, social, and economic [2].Changes in the quality of the aquatic environment are external factors that greatly influence the growth of Kappaphycus alvarezii seaweed and the influence of internal factors within the seaweed itself.External factors consist of physical factors (temperature, currents, light, tides, and transparency), chemical factors (salinity, pH, and nutrients) and biological factors related to water fertility and the presence of herbivores and parasitic organisms.Internal factors that influence seaweed growth are thallus and age [3].Environmental influences related to water quality, pollution, pest, disease attacks and hydrooceanographic conditions have a major impact on seaweed cultivation businesses.
Seribu Islands Regency is one of the locations for seaweed cultivation which experienced a significant decline in production from 3,432 tons in 1998 [4] to 116.65 tons in 2020 [1].The impact of changes in environmental quality has significantly resulted in seaweed production decreasing.The focused research was carried out on Panggang Island, Seribu Islands Regency as one of the seaweed cultivation locations which experienced a decline in seaweed production.The aim of this research is to determine the current status of water quality through analyzing suitability class for cultivating Kappaphycus alvarezii seaweed and developing the concept of sustainable seaweed cultivation using a System Dynamic modeling approach.It is hoped that the research results can be used as consideration in efforts to improve and develop seaweed cultivation in Panggang Island, Seribu Islands Regency.

Method 2.1. Data collection and analysis of water quality.
The research was conducted in April-May 2023 in the waters around Panggang Island, Seribu Islands Regency which is part of the Seribu Islands Regency which is experiencing a decline in seaweed production.Data collection was carried out by measuring water quality and taking water samples including physical, chemical, and biological parameters which were collected directly in the field at 12 sampling points (Figure 1).Pollution index analysis was carried out to determine the level of pollution in the waters of the Panggang Island, Seribu Islands Regency.Equipment used for measuring water quality at sampling locations includes: water quality checker (Horiba U5000G), Secchi Disk, JFE Current Meter (Infinity Series) AEM 1618, planktonet, Vacuum pump, 0,42 µm filter paper to filter TSS and Chlorophyll-a samples, Colorimeter (Hach DR900) for nitrate, phosphate and ammonia analysis.

Physical and chemical data analysis.
Analysis of physical parameters, especially current speed, is carried out by downloading and processing data from the current meter.Physical parameters including temperature, transparency, and turbidity are measured directly in the field.The chemical parameters include salinity, pH, and Dissolved Oxygen, which are measured directly in the field using water quality checker equipment.Nitrate, ammonia and phosphate are analyzed in the field using a spectrophotometer, and total suspended solid, oil, and grease are analyzed in the laboratory.

Biological data analysis.
Analysis of biological parameters including chlorophyll-a and plankton was carried out in the Fisheries Laboratory, Laptiab, KST BJ.Habibie BRIN, Serpong, Banten.Plankton data analysis include plankton identified by using Olympus cx22led binocular microscope with 40-100 times magnification.Take 1 mL of the homogenized samples, place it on a Sedgewick Rafter Counting Cell (SRC), cover it with a cover glass, then proceed to identify and calculate the abundance.Plankton identification should be carried out according to the plankton identification book.The abundance of plankton calculated referring to APHA [5]: Description: N = Plankton abundance (cell/m 3 or ind/m 3 ); n = number of observed plankton (cell); A = Volume of filtered water (100 L); B = Volume of filtered sample (30 ml), C = Observed water volume in SRC (1 ml); D = Number of squares counted SRC (1,000 mm 2 ); E = Number of squares counted for observed SRC, with the square sizes of 300 mm² for Phytoplankton and 2,000 mm² for Zooplankton."Calculation of the Diversity Index or Diversity of plankton types (H') uses the Shannon-Wiener formula Stilling [6], Parson et al, [7]: Description: H': Shannon-Wiener diversity index; Pi: ni/N; ni: number of individual species-1 th ; N: total number of individuals.Evenness index was determined using the following formula Poole [8], Odum [9]: Description: E = Evenness index; H' = Shannon-Wiener diversity index; Hmax= ln S; S = number of genera.
Dominance index was determined using the following formula Simpson Odum, [9]: Description: D = Simpson dominance index; ni = number of individual species-i th ; N = total number of individuals; S = number of genera.

Pollution Index analysis.
Pollution Index analysis is used to determine the status of water pollution at seaweed cultivation locations around Panggang Island.The analysis of the water pollution index refers to Minister of Environment Decree No. 115/2003 regarding Guidelines for Determining the Status of Seawater Quality.The results of this analysis are whether the water status is in good condition, slightly polluted, fairly polluted or heavily polluted (Table 1).Pollution Index analysis is carried out using the formula [10]: Description: PI = Pollution Index; Ci = Monitoring Concentration Value; Lj = Quality Standard Value.

Evaluation of water quality for suitability of seaweed cultivation locations
There are six stages for evaluating the suitability of seaweed cultivation locations in this research.The first data analysis stage, determining the assessment number, namely 3 = good; 2= moderate and 1= poor.The second stage, weighting according to requirements refers to the level of parameters that are very determining.Parameters that are very suitable are given a weight of 3, parameters that are quite suitable are given a weight of 2 and parameters that are not suitable are given a weight of 1 (Table 2).The third stage, determine the score value using the score value formula = ΣScore x Weight.Fourth stage, data obtained in the field, processed and analyzed for determine the suitability of water quality for cultivating Kappaphycus alvarezii seaweed, using criteria contained in Table 2.The fifth stage, determines whether the location status is very suitable, suitable, and not suitable.
The scoring of the evaluation results is obtained using the following equation Nurdin et al., [11]: Description: Ci = range between classes; n = number of planned classes

System Dynamic Model approach
System dynamics methodology as an approach for creating simulation models in order to carry out policy analysis (developing strategies and formulating policies) [18].The benefits of system dynamics include helping make better decisions, more efficient planning, and more effective problem solving in various contexts.System dynamics includes the following elements: variables, time, differential equations, balance and dynamics, simulation and analysis.Several factors that influence seaweed production in Panggang Island, Seribu Islands can be considered as variables in system dynamics, including environmental water quality, human resources, technology used and the seaweed itself.Furthermore, system dynamics can be used to test various policy scenarios by considering social and environmental impacts in the long term.

Water quality around Panggang Island
The results of the measurements of water quality of Panggang Island waters include physical, chemical and biological parameters are shows on Table 4.According to water quality parameter data collected on the ground (Table 4), the current velocity of the water ranged from 2 to 40 cm/s, indicating that the water is relatively calm, temperature was relative stable i.e. ranging from 29.44 to 30.19 0 C with an average value of 29.94 0 C, the transparency of water ranged from 4.5-10 m, indicating adequately high sunrays intensity penetrating the water and suitable for seaweed growth.Current is needed to prevent extreme changes in water quality such as temperature, salinity, pH, dissolved oxygen and others [19].
The salinity, pH and DO of which also indicated that the water was adequately stable.Salinity ranges from 28.40 to 29.00 ppt, pH ranges from 7.94 to 8.21, and dissolved oxygen (DO) levels are approximately 4.30 to 5.50 mg/L, with a mean value of 4.48 mg/L.Nutrient analysis indicates relatively low concentrations of phosphate, ranging from 0.06 to 0.28 mg/L, with an average value of 0.15 mg/L.On the other hand, nitrate concentrations are relatively high, ranging from 1.60 to 6.30 mg/L, with an average value of 3.70 mg/L (Table 4).3.7 mg/L (Table 4), exceeding the parameter of 0.9 -3.5 mg/L [20].Oil and grease analysis results were 9 mg/L to 36 mg/L with an average of 23 mg/L exceeding the limit of 1 mg/L [17] (Government Regulation/PP No. 22/2021).The high concentration of nitrates and oil are probably caused by domestic waste, transportation and sea ports activities from Panggang Island and the surrounding islands in Seribu Islands Regency.It is feared that the high concentration of oil in the waters will inhibit the growth of seaweed.
Dissolved oxygen measurements at several sampling stations are relatively low, namely stations 3, 4, 5, 6, 7, 9, and 10 (Table 4), however, it is still close to 5 mg/L as the minimum requirement for marine biota [17].The results of current velocity measurements are generally relatively low, especially at station 4 (3-18 cm/s), station 5 (2-14 cm/s), and station 6 (3-14 cm/s) (Table 4).This indicates that the water is relatively calm, similar to the findings of a study by Effendi et al [21] on the sandbar of Panggang Island, Seribu Islands Regency.In their research, the current predominantly flowed southeast-south, with an average speed of 13.5 cm/s and a range between 4.4-19.1 cm/s.This result does not meet the requirements for seaweed cultivation, which typically necessitate current velocities of 20-40 cm/s [12].On the other hand, an appropriate current velocity can enhance nutrient loading, consequently increasing nutrient and carbon dioxide absorption by reducing diffusion in the boundary layer around the algae surface [22].Parameters that deviate from the suitable range may adversely seaweed production.

Plankton analysis
The results of the plankton analysis revealed a range of 20-43 taxa, and the plankton abundance in the waters around Panggang Island varied from 36 to 9,070 ind/L (Table 5).The abundance has not reached endangers for the other lives organisms because blooming will occur when the abundance reaches 5x10 5 to 2x10 6 cells/L [23].0.8 0.9 0.8 0.8 0.9 0.9 0.4 0.7 0.3 0.2 0.6 0.9 Dominance index (D) 0.1 0.1 0.1 0.1 0.1 0.1 0.5 0.2 0.7 0.8 0.2 0.1 Chaetoceros sp.demonstrated dominance and widespread distribution across almost all stations, particularly notable at stations 9 and 10, where the abundance reached 7,470 cells/L and 2,277 cells/L (Figure 2).The high abundance of Chaetoceros sp. is probably influenced by rainy season factors during sampling.The composition of Chaetoceros sp. is also predominant, constituting a high percentage at nearly all stations, particularly noteworthy at stations 9 and 10, where it reaches 84.26% and 90.04%, respectively (Figure 3).Chaetoceros sp.belongs to the diatom group of plankton, serving as a natural food source for the larval and juvenile phases of aquatic biota, including shrimp, fish, abalone, and mollusks.Classified under the Bacillariophyta class, Chaetoceros sp. is also considered a bioindicator of organic material pollution in waters, suggesting that the waters around Panggang Island, Seribu Islands Regency are contaminated by organic substances.
The diversity index (H') ranges between 0.9 and 3.1 (Figure 3), suggesting a variation in the stability of the biota community from unstable to stable.Stations 9 and 10 are identified as unstable (H' 0.9 and 0.6 < 1), stations 1 to 8 and 11 exhibit moderately stable biota communities, while station 12 indicates stable waters (H' 3.1 > 3) [6].The evenness index (E) ranges from 0.2 to 0.9, indicating a low level of uniformity between species (E < 1), and the dominance index (D) varies between 0.1 to 0.7 (Table 5), suggesting that no species extremely dominate the waters (D < 1) [9].The results of chlorophyll-a analysis at all stations varied, with the lowest value recorded at station 5 (0.36 μg/L) and the highest at station 8 (4.24 μg/L), averaging 1.50 μg/L.The chlorophyll-a analysis, in general, indicates that the waters fall into the oligotrophic range (0-2 μg/L) and meso-oligotrophic range (2-5 μg/L) [24].Oligotrophic waters are characterized by low fertility, while meso-oligotrophic waters have a moderate level of fertility.Oligotrophic waters represent a trophic status characterized by low nutrient levels [25].This condition could be one of the causes of the decline in seaweed production the Panggang Island, Seribu Islands Regency, as oligotrophic and meso-oligotrophic waters may not provide the optimal nutrient levels required for robust seaweed growth.

Analysis of water quality suitability for seaweed cultivation
The results of the water quality suitability calculation at stations 1-12 show a total suitability class value of 50-55 (Table 6), included in the class S (Suitable) (Table 3).The total suitability value is greatly influenced by determining the weighting of each parameter and the results of water quality measurements in the field.Several parameters that need further attention include nitrate exceeding 3.5 mg/L and oil & grease exceeding 1 mg/L and even reaching 40 mg/L.Waste oil and grease forms a thin layer and covers the surface of the water, thereby inhibiting the process of dissolving oxygen into the water [26].7).Based on the Pollution Index calculation results, it indicates pollution in the waters around Panggang Island, not in compliance with government requirements, which mandate no pollution [17].Although the evaluation results classify the waters around Panggang Island, Seribu Islands as suitable for cultivation, pollution requires serious attention due to its potential impact on seaweed production.

The concept of a System
Dynamic Model approach for managing and predicting future seaweed production.The use of system dynamic models is expected to produce many alternative solutions and appropriate policy decisions [18].To represent the relationship and feedback process, a Causal Loop Diagram (CLD) needs to be prepared.Preparation of CLD to describe the factors causing the decline in Kappaphycus alvarezii seaweed production.One CLD can be developed by considering four factors that influence seaweed production, namely environmental water quality, seaweed, human resources and technology (Figure 4).Based on the CLD, a Stock Flow Diagram (SFD) can be created that can be used to predict production when one of the factors or variables changes.An example of a production change influenced by environmental water quality variables comprises physical, chemical, and biological parameters (Figure 5).Environmental water quality factors consisting of physical, chemical and biological parameters can influence the growth rate and production of seaweed.Seaweed production is also influenced by the seaweed itself in terms of quality, type and quantity.Human resources also influence seaweed production related to quantity, expertise, and income.The technological factors used influence seaweed production, whether the long line method, off bottom method or floating raft method.
The causal relationship of the four factors in CLD is than calculated using an algorithm for each variable according to the level of influence to obtain a predicted value for seaweed production.The next production scenario can be created by changing the variable values in the CLD.Changes in the value of each variable can be used to consider developing strategies to improve factors that influence the production of Kappaphycus alvarezii seaweed.Efforts to improve water quality can be carried out using a system dynamic model approach to sustainable environmental management and predict future production.

Conclusion
Despite some parameters not meeting the requirements, particularly nitrate, oil and grease, the environmental water quality status in the seaweed cultivation area in the Panggang Island, Seribu Islands is still classified as 'Suitable Class.'However, it's noteworthy that the Pollution Index falls under the category of "Fairly Polluted".Therefore, concerted efforts for improvement, especially in mitigating factors such as nitrate levels, oil and grease, are necessary.The Causal Loop Diagram model in System Dynamics can be used to formulate improvement strategies by considering four crucial factors: environmental water quality, technology, human resources, and seaweed.

Figure 1 .
Figure 1.Map of sampling locations in the waters surrounding Panggang Island, Seribu Islands Regency.

Figure 2 .
Figure 2. The plankton abundance in the waters around Panggang Island, Seribu Islands Regency.

Table 2 .
Matrix of water quality suitability for Kappaphycus alvarezii seaweed cultivation.= 18, therefore the interval value of each class is 18 (Tabel 3).The sixth stage, determining the water quality suitability class of the seaweed cultivation location (Tabel 3).

Table 4 .
Presents the results of water quality measurements in the waters surrounding Panggang Island, Seribu Islands Regency.In general, the results of water quality measurements are adequately suitable for seaweed cultivation, although there are several parameters that are not suitable, namely: nitrate, oil and grease, DO and current velocity.The results of nitrate analysis ranged from 1.6 mg/L to 6.3 mg/L, with an average of *) 100%

Table 5 .
Recapitulation of plankton analysis in the waters around Panggang Island, Seribu Islands Regency.

Table 6 .
Results of suitability classes for seaweed cultivation locations in the waters around Panggang Island, Seribu Islands Regency.Pollution Index The environmental quality of seaweed cultivation waters on Panggang Island, Seribu Island is very susceptible to being influenced by several sources of pollution, including; domestic waste, sea transportation, oil mining, sea port activities and others, therefore it is necessary to calculate the pollution index.The results of the Panggang Island, Seribu Islands water pollution index calculations indicate that the waters are categorized as 'Fairly Polluted' (Table

Table 7 .
Results of Pollution Index calculations in the waters around Panggang Island, Seribu Islands Regency.