Land Suitability Assessment for White Shrimp (Litopenaeus vannamei) Ponds Using Geographic Information System in the Mulyorejo Subdistrict, Surabaya, East Java

Introduction

Mulyorejo Subdistrict is a coastal area located in the second development unit of Kertajaya, Surabaya City. The total area of this subdistrict is 11.94 km2 and a population density of 87,801 people in 2016 (1). According to the Surabaya City Spatial Plan (RTRW) for the period 2010-2030, the coastal zone in Mulyorejo Subdistrict is designated as a protected mangrove forest area that is integrated with ponds and marshes ecosystems.

According to Article 6, paragraph 1 of Law Number 45 of 2009 on Fisheries, fisheries management within the Indonesian Exclusive Economic Zone (WPP-RI) aims to achieve optimal and sustainable benefits while ensuring the conservation of fishery resources. Therefore, the utilization of fisheries and marine potentials must be well-managed and responsible to ensure sustainable activities and become a major capital for Indonesia's development in the present and future (2). Marine and fisheries development should be oriented towards environmentally friendly fisheries development, prioritizing the conservation of biological resources, and being carried out efficiently and sustainably (3). Hence, this research aims to analyze the land suitability for the development of L. vannamei ponds in Mulyorejo, Surabaya, East Java.

Experimental Section

Water Quality Observation

Water quality observations were conducted with a single measurement at each station, starting from 8:00 AM until 3:00 PM, for a duration of 5 days and the weather was cloudy due to the rainy season. Salinity measurements were taken using a digital salinometer, pH levels were measured using a digital pH meter. In contrast, phosphate and nitrate measurements were obtained by collecting water samples and analyzing them using a refractometer at the Freshwater Fish Culture Laboratory, Sumberpasir, Faculty of Fisheries and Marine Sciences, Brawijaya University, Malang.

Solid Data Collection

Soil data collection was performed using a soil auger. Soil samples were collected by inserting the auger vertically into the soil to a depth of 50 cm. The collected soil samples were then placed in plastic bags and labeled with paper labels. Soil C/N ratio analysis was conducted at the Agricultural Crop and Horticulture Agribusiness Development Center (UPT Pengembangan Agribisnis Tanaman Pangan dan Hortikultura), Bedali, Lawang. Soil type data were obtained from digital data released by the Agriculture Land Resources Center (BBSDLP) in 2010.

Climate Data Collection

Climate data was obtained from the daily climate reports of the past five years [2014-2018] released by the official website of the Meteorology, Climatology, and Geophysics Agency (BMKG-online). The data were collected from three stations: BMKG Maritim Perak I Surabaya, BMKG Perak II Surabaya, and BMKG Juanda. These three stations were selected due to their proximity to Surabaya City.

Database Processing

The collected data were used to determine the rainfall, air temperature, and evaporation rate in Surabaya City. Field observations involved measuring the values of temperature, salinity, pH, nitrate, and phosphate in potential pond areas. The coordinates of the water quality data collection stations were determined using GPS. Additionally, field investigations aimed to match the visual conditions in the imagery with the actual visuals on-site, aiding in the creation of land use maps.

Feasiability Analysis

The land suitability classification was performed by creating a suitability matrix to assess the suitability level based on assigning scores to the limiting factors for L. vannamei cultivation (Table 1). After obtaining the suitability score ranges for each parameter, they were processed using the Reclassify tool in ArcGIS 10.2 to derive three suitability classes: Good, Moderate, and Poor. The Suitability maps for each parameter were then overlaid using the Union tool. The score values for each attribute of the suitability parameters were summed using the Field Calculator tool to obtain the total suitability score for each parameter.

Table 1. Assessment of Parameter Suitability for L. vannamei Ponds.

Note: Modified from references (4-8).

Result and Discussion

General Condition

The district of Mulyorejo is geographically located in the eastern part of Surabaya City, with coordinates ranging from 07°14' to 07°17' S latitude and 112°45' to 112°50' E longitude. It is a low-lying area with an elevation ranging from 2 to 7 meters above sea level and a land slope of 0-3%. Administratively, Mulyorejo District is bordered by Bulak District to the north, the Madura Strait to the east, Sukolilo District to the south, and Gubeng and Tambaksari Districts to the west.

The total area of Mulyorejo District is approximately 1,841 hectares and is divided into six urban villages: Manyar Sabrangan Urban Village (approximately 165 hectares), Mulyorejo Urban Village (approximately 303 hectares), Kejawan Putih Tambak Urban Village (approximately 325 hectares), Dukuh Sutorejo Urban Village (approximately 264 hectares), Kalisari Urban Village (approximately 642 hectares), and Kalijudan Urban Village (approximately 142 hectares). The study area for this research is located in Kalisari, Dukuh Sutorejo, and Kejawan Putih Tambak Urban Villages.

The field observation was conducted in three urban villages: Kalisari, Kejawan Putih Tambak, and Dukuh Sutorejo. The selection of these locations was based on the circular letter issued by the City Government regarding the Spatial Planning and Regional Plan of the City, which prioritized the eastern coastal areas of Mulyorejo District as a mangrove protected forest area integrated with aquaculture ponds. The observation parameters included water quality, geophysics, and climate, which were marked using GPS coordinates.

Table 2. Water quality at observation stations.

Figure 1. Administrative Boundary Map of Mulyorejo District

Figure 2. Map of Mulyorejo with land use (a), salinity distribution (b), nitrate distribution (c), pH distribution (d), Phosphate distribution (e), soil types (f), soil C/N ratio (g), evaporation rate (h), rainfall (I), and air temperature (j)

In shrimp pond aquaculture, the water used must meet specific criteria for the survival of shrimp (9). The water quality parameters measured in this study included acidity level (pH), salinity, nitrate, and phosphate. Sampling points for water quality were taken from various locations in the three urban villages, including inlet and outlet of the ponds, pond water, and other water channels. The results of the water quality observations can be seen in Table 2 and the map of parameter distribution is presented in Figure 2.

Figure 2A depicts the land use map of Mulyorejo District, which includes shrimp ponds, mangrove forests, settlements, and vacant land. Mangrove areas are suitable for the cultivation of L. vannamei. Further research is still needed to understand the relationship between the shrimp ecosystem and mangroves. Previous studies have indicated negative impacts on shrimp production within mangrove ecosystems (10).

Water quality parameters such as salinity, nitrate, pH, and phosphate are illustrated in Figures 2B to 2E. The distribution pattern of water salinity in the Mulyorejo District, ranging from 0-25 ppt, which aligns with the accepted salinity standards for L. vannamei cultivation, falling between 10-25 ppt, with the optimal range being 15-25 ppt. Nitrate distribution in the same area, which spans from 0.050 to 0.262 ppt. This nitrate concentration is vital as it stimulates the growth of essential natural food sources like klekap, plankton, and algae for fish, a critical factor in shrimp farming. The algae, particularly phytoplankton, thrive optimally at nitrate levels between 0.9-3.5 mg/L (11). Examining the pH values in Figure 2D reveals a range from pH 7.3 to 8.7 within the study locations, with the lowest pH in Kejawan Putih Tambak and Kalisari, and the highest in Dukuh Sutorejo and Mulyorejo neighborhoods. However, all pH levels fall within the suitable range of 7.5-8 for L. vannamei cultivation. Lastly, the distribution of phosphate, ranging from 0.043 to 1.705 ppt, indicating a natural nutrient supply from weathering processes and human activity waste. The phosphate content observed aligns with the optimal range for shrimp farming, as suggested by a reference (8), which is >0.2 ppt. Collectively, these observations suggest that the environmental conditions in the research location are conducive to L. vannamei cultivation.

Figure 2F shows that the land in Mulyorejo District consists of typic endoaquepts and typic epiaquepts soil types, which belong to the alluvial soil group. Land suitable for pond cultivation is characterized by sufficient water saturation, preventing rapid water infiltration (12). Conversely, soil types with low water saturation can hinder pond cultivation activities. Typic endoaquepts soil has a water saturation level of 75% or higher, while typic epiaquepts has a saturation level between 50-75%. Therefore, this land is considered suitable for L. vannamei cultivation. Figure 2G displays a C/N ratio range of 1-16. C/N ratio that is too high can potentially lead to plankton blooming, while a ratio that is too low can make it difficult to cultivate natural food sources. The optimal C/N ratio for L. vannamei cultivation land is in the range of 5-15 (7). Therefore, it can be concluded that the land in Mulyorejo District is still suitable for L. vannamei cultivation. Figure 2H depicts the evaporation rate in Mulyorejo District, which does not significantly differ and ranges from 3.49 to 3.62 mm/day. The lowest evaporation rate occurs from April to July, while the highest evaporation rate is observed from September to November (13). Therefore, the climatic conditions in Mulyorejo District are considered suitable for L. vannamei cultivation. Figure 2I explains the rainfall intensity in Mulyorejo District, which ranges from 1,562 to 2,201 mm/year. The variation in rainfall distribution at the research location is not significantly different and still falls within suitable conditions for L. vannamei cultivation. Figure 2J shows the air temperature in Mulyorejo District ranging from 28.25 to 28.85 °C. This range does not vary significantly and is still suitable for pond cultivation. High fluctuations in air temperature during extreme periods can affect L. vannamei pond cultivation activities (14), as excessively high or low temperatures can disrupt shrimp metabolism balance, making them more susceptible to diseases and mortality. Extreme temperatures occur in April - May and October – November (15).

The score values for each attribute of the feasibility parameters are summed using the Field Calculator tool, resulting in the total feasibility score for each parameter. The analysis results after overlaying the data can be seen in Figure 3A below.

Figure 3. The assessment of the feasibility of shrimp pond cultivation land in Mulyorejo District after performing the overlay (A) and after being categorized (B)