Evaluation of the Abundance of Plankton Benthos in Waters Around the Steam Power Plant

The Banten 2 Labuan Steam Power Plant (SPP) is located in Sukamaju Village, Labuan District, Pandeglang Regency, Banten Province, within the coastal waters of the Sunda Strait [1]. The plant has an installed capacity of 600 MW (2 × 300 MW) and supplies electricity to the Java–Bali power system. Its operation employs an open-cycle cooling system, in which seawater is continuously drawn into the condenser and discharged at a higher temperature than the ambient seawater, generating thermal waste [1].

Monitoring seawater quality in the vicinity of the SPP is essential because changes in physicochemical conditions can directly affect aquatic biota, including coral reefs and other marine organisms. In addition to thermal discharge from power plant operations, seawater quality may be influenced by land-based activities, such as domestic, industrial, and agricultural inputs, which can degrade water quality and disrupt coastal ecosystems [2].

Assessing seawater quality around coal-fired power plants poses significant challenges due to the number and complexity of parameters to be evaluated, including temperature, pH, salinity, dissolved oxygen, and coliform bacteria. Furthermore, surrounding anthropogenic activities, such as industrial operations and riverine waste discharge, may intensify environmental pressures on coastal waters. To address these challenges, this study applies periodic and systematic seawater sampling at multiple monitoring points around the Labuan 2 SPP, including areas potentially influenced by waste inputs.

Previous studies have demonstrated the importance of plankton communities as indicators of aquatic environmental conditions. Research on carbon absorption by phytoplankton has been conducted in Lake Maninjau, Indonesia [3]. In contrast, investigations of zooplankton and phytoplankton distributions in anoxic lake layers have been reported in Lake Fukami-Ike, Japan [4]. In addition, zooplankton community structure has been used as an indicator of trophic status in reservoirs in Chelyabinsk, Russia [5]. These studies highlight the sensitivity of plankton communities to environmental changes across diverse aquatic systems.

Water quality assessment using the Pollutant Index (PI) method has been widely applied in marine, riverine, and lacustrine environments. Applications of this method in Indonesia have revealed heavily polluted conditions in the Cimahi River, West Bandung Regency [6], as well as in several reservoirs, including those at the Cimahi City Government Office [7], Setiamanah Reservoir [8], and Cibabat Reservoir [9]. These findings demonstrate the effectiveness of the PI method in identifying water quality degradation associated with anthropogenic pressures.

The present study addresses existing knowledge gaps by examining seawater quality in relation to plankton and benthos communities in the coastal waters surrounding the Labuan 2 SPP. By integrating the PI method with biological indicators, this study aims to evaluate the influence of power plant operations and surrounding human activities on seawater quality and ecosystem structure. The results are expected to provide insights into the ecological condition of the study area and to support sustainable management of coastal waters affected by industrial activities.

This study was conducted at seven monitoring points surrounding the Labuan 2 Banten SPP to evaluate the relationship between seawater quality and the structure of plankton and benthos communities. Biodiversity was assessed using the Shannon–Wiener diversity index, the uniformity index, and the Simpson dominance index, which together provide complementary insights into community composition and ecological condition.

The application of these indices enables the integration of biological indicators with physicochemical water quality assessment. Changes in diversity, evenness, and dominance patterns reflect environmental stress and can be used to identify areas potentially affected by anthropogenic activities. By combining indices that capture both rare and dominant species, this study provides a balanced evaluation of community structure in coastal waters influenced by power plant operations.

The significance of this research lies in its contribution to understanding the ecological condition of seawater in the vicinity of a coal-fired power plant using an integrated biological approach. The findings are expected to support environmental monitoring programs and inform coastal management strategies by linking seawater quality to plankton and benthic community responses.

Seawater quality analysis was conducted at the Environmental Quality Control Laboratory of the Tirtawening Regional Drinking Water Company, Bandung City, West Java Province. Seawater sampling followed the Indonesian National Standard SNI 6964-8-2015 for seawater sampling methods. Benthos sampling was performed in accordance with SNI 13-4718-1998, which specifies procedures for benthos collection in public waters. Plankton sampling followed SNI 06-3963-1995, which outlines methods for identifying and quantifying plankton in aquatic environments.

All sampling procedures adhered strictly to the relevant SNI guidelines to ensure consistency and reliability across the seven monitoring points. Standardized protocols were applied for sample collection, preservation, and handling. Field personnel were trained to implement identical procedures at each sampling location, and all field equipment was regularly calibrated to minimize measurement errors. These measures were implemented to ensure data comparability and to reduce potential bias associated with sampling variability.

In addition to biological sampling, several environmental variables were measured, including water transparency (brightness), Total Suspended Solids (TSS), and water temperature. These parameters were selected for their influence on plankton and benthic communities. Water transparency affects light penetration and photosynthetic activity, while TSS represents suspended inorganic and organic particles that can influence habitat conditions. Water temperature was recorded because it involves physical, chemical, and biological processes in marine ecosystems [2].

Field sampling was conducted in July 2021 during the dry season. Supporting secondary data were obtained from the management of the Labuan 2 Banten Steam Power Plant. Spatial conditions of the study area were documented using aerial photographs captured with a DJI Phantom Pro 4 drone. The locations of sampling points are presented in Table 1 and illustrated in Figure 1.

Biodiversity was assessed using established diversity indices to describe community structure based on species composition and abundance. These indices were applied to quantify variations in plankton and benthos communities across the monitoring points [10].

Biodiversity indices were used to evaluate variations in community structure among sampling locations, potentially driven by differences in environmental conditions and anthropogenic influences. Species diversity was used as an indicator of community structure, reflecting both species richness and the distribution of individuals within a community. Communities with higher diversity are characterized by a greater number of species with relatively even abundances, whereas lower diversity indicates dominance by a limited number of species [10].

The Simpson Diversity Index was applied to quantify species dominance within each community, with values ranging from 0 to 1. Lower index values indicate more stable environmental conditions, while higher values suggest increased dominance and potential ecological imbalance [11].

The Shannon–Wiener diversity index ($H^{\prime}$) was calculated to assess species diversity based on the number of species and their relative abundances [12]. This index is sensitive to changes in community composition and was used to compare biodiversity among sampling points. The Shannon–Wiener index was calculated using Eq. (1) [13].

where, $ni$ is the number of individuals/organisms of each species, $i$ and $N$ are the total number of individuals/organisms of all species, with the following provisions:

$H^{\prime}$ $<$ 2 shows low species diversity, low distribution of individuals per species, low community stability, and polluted water conditions.

2 $<$ $H^{\prime}$ $<$ 3 shows moderate diversity, individual numbers distribution, and moderately polluted water stability.

$H^{\prime}$ $>$ 3 shows high diversity, high distribution of individuals per species or genera, high community stability, and the waters are still unpolluted.

The Uniformity Index is presented in Eq. (2) [13].

where, $E$ is the Uniformity Index, $H^{\prime}$ is the Diversity Index, and $s$ is the number of species, with the following provisions:

$E$ $<$ 0.4, the level of population uniformity is trim;

0.4 $<$ $E$ $<$ 0.6, the level of population uniformity is moderate;

$E$ $>$ 0.6, the degree of uniformity of large populations

The Dominance Index is a parameter that states the level of centralized dominance (mastery) of species in a community. It is calculated using the Simpson formula presented in Eq. (3).

where, $D$ is the Simpson Dominance Index, $ni$ is the number of individuals/organisms of each species $i$, and $N$ is the number of individuals/organisms of all species, with the following provisions:

0 $<$ $D$ $<$ 0.5, if no type dominates;

0.5 $<$ $D$ $<$ 0.8, if there are dominant types and stable conditions;

0.8 $<$ $D$ $<$ 1, if there is a type that dominates.

The dominance index ranges from 0 to 1, where the smaller the Dominance Index value indicates that no species dominates; conversely, the greater the dominance, the more certain species dominates [10]. The method used to determine the quality status of seawater is the PI method, referred to in the Decree of the Minister of Environment No. 115 of 2003. The quality value category (PI) is shown in Table 2.

The construction and operation of the Banten 2 Labuan SPP support the national electricity supply program with an installed capacity of 600 MW. The plant uses seawater as its primary cooling source, with an estimated intake of approximately 90,000 m$^3$/h. Of this volume, about 89,585 m$^3$/h is used in the condenser to cool steam after it passes through the turbine [1].

Electricity generation at the SPP is based on coal combustion to heat water in the boiler, producing superheated steam at approximately 538 ℃ and 169 kg/cm$^2$. The steam drives a high-pressure turbine, converting thermal energy into mechanical energy, which is subsequently transformed into electrical energy by the generator and distributed to consumers [1].

Seawater quality status was determined using the PI method, with reference to the quality standards specified in Appendix VIII of Government Regulation of the Republic of Indonesia No. 22 of 2021 for marine biota. The calculation results indicated that all measured parameters complied with the applicable quality standards. The PI values at sampling points 1–7 ranged from 0.50 to 0.86, suggesting that seawater quality at all locations met the established standards.

Figure 2 illustrates the seawater quality status at monitoring points 1–7. Seawater quality in the study area is influenced by SPP operational activities, including rainwater runoff from coal storage areas, coal transportation and unloading at the jetty, and sediment dredging in surrounding waters [1]. Additional inputs originate from the Cibama River, which flows across the SPP activity area near the southern canal. This river is subject to significant anthropogenic pressure, particularly from domestic wastewater discharge and solid waste from nearby settlements, which may degrade local seawater quality [1].

Plankton are aquatic organisms that play a key role in regulating water conditions and supporting aquatic food webs as primary trophic components, particularly under changing environmental conditions [16], [17]. The results of the phytoplankton diversity analysis are presented in Table 3, while the zooplankton composition is shown in Table 4.

A total of 27 phytoplankton species were identified across all monitoring points. The Shannon–Wiener diversity index ($H^\prime$) ranged from 0.876 to 2.451, indicating moderate diversity across the transects. This condition is associated with relatively high-water transparency, which enhances light penetration and supports photosynthetic activity. The uniformity index ranged from 0.323 to 0.806, reflecting generally high species evenness. In addition, the Simpson dominance index varied between 0.129 and 0.663, suggesting the absence of strong dominance by a single species.

Overall, the phytoplankton community structure corresponds to seawater quality conditions that meet established quality standards. As reported in previous studies, increases in water pollution are typically associated with reduced diversity and community instability, highlighting the sensitivity of phytoplankton communities to changes in water quality [18].

Skeletonema was identified as the dominant phytoplankton genus and was consistently present at all seawater monitoring locations. This genus commonly dominates phytoplankton communities due to its high adaptability, rapid growth rate, and efficient nutrient uptake. Skeletonema can thrive under varying environmental conditions, including fluctuations in temperature, salinity, and nutrient availability. Its filamentous morphology enhances buoyancy and light exposure, supporting efficient photosynthesis and contributing to its ecological competitiveness.

The dominance of Skeletonema influences food web dynamics and biogeochemical processes in coastal ecosystems. Owing to its relatively high biochemical content, this genus also serves as an important natural food source for higher trophic levels [19]. However, its distribution and persistence are closely associated with salinity, which plays a critical role in regulating phytoplankton physiological processes. Salinity is therefore a key factor controlling algal productivity and community composition in coastal waters [19].

Zooplankton analysis identified 17 taxa across the sampling transects. The Shannon–Wiener diversity index ($H^\prime$) ranged from 1.628 to 2.027, indicating moderate diversity. The evenness index ranged from 0.651 to 0.821, reflecting relatively even species distribution, while the Simpson dominance index ranged from 0.163 to 0.267, indicating low dominance. These values suggest a stable zooplankton community structure consistent with seawater quality conditions that meet established standards.

Zooplankton play a crucial role in aquatic food webs by transferring energy and organic matter from primary producers to higher trophic levels and are widely used as indicators of ecological condition due to their sensitivity to changes in physical and chemical water properties [20]. The dominant zooplankton taxon observed was Temora, a copepod that functions as a primary consumer linking phytoplankton to higher trophic levels. Copepods typically comprise 70–90% of marine zooplankton biomass and serve as a significant food source for pelagic fish, underscoring their ecological significance in aquatic ecosystems [20].

Benthos are essential components of aquatic ecosystems and are highly sensitive to changes in environmental conditions due to their relatively sedentary nature [21]. These organisms utilize organic matter deposited on the seabed as a nutrient source, making them strongly influenced by variations in water quality and sediment characteristics. Consequently, benthic communities are widely used as biological indicators of marine environmental conditions. The benthos data obtained in this study are presented in Table 5.

A total of ten benthic taxa were identified across the monitoring points. The Shannon–Wiener diversity index ($H^\prime$) ranged from 0.347 to 1.052, indicating low to moderate diversity along the transects and suggesting dominance by a limited number of taxa at several locations. Benthic diversity is closely associated with water temperature, which influences growth, metabolism, and spatial distribution. Elevated or fluctuating temperatures may reduce benthic diversity, particularly for species with narrow thermal tolerance ranges.

No benthic organisms were recorded at monitoring point 4. The uniformity index ranged from 0.500 to 0.918, indicating moderate evenness in species distribution at most locations. The Simpson dominance index ranged from 0.200 to 1.000, reflecting moderate dominance patterns within the benthic community.

At monitoring points 2–6, benthic diversity values ($H^\prime$ $<$ 1) indicate low species diversity, uneven individual distribution, and reduced community stability, which may be associated with elevated water temperatures ($>$30 ℃) and environmental disturbances such as dredging activities and pollutant inputs from the Alabama River. In contrast, monitoring points 1 and 7 exhibited higher diversity values ($H^\prime$ $>$ 1), indicating moderate community stability and environmental conditions that meet established seawater quality standards.

The dominant benthic taxon observed was Arenicola sp., a polychaete characterized by high secondary production and a relatively short life cycle. This species plays a significant ecological role in marine food webs due to its high calorific and protein content, serving as an essential food source for economically valuable fish species. In addition, polychaetes contribute to sediment stabilization, sediment oxygenation, and biogeochemical cycling by facilitating the transport and transformation of organic matter within marine sediments [22]. A comparison of benthic community characteristics from this study with those reported in other locations is presented in Table 6.

The assessment of seawater quality around the Banten 2 Labuan SPP using the PI indicates that all monitoring points fall within the category of seawater meeting established quality standards. The observed PI values reflect generally favorable environmental conditions in the study area, although continued vigilance is required to prevent potential degradation.

The structure of plankton and benthos communities further supports this assessment, as moderate to high biodiversity levels and the absence of strong species dominance indicate a relatively stable and balanced ecosystem. The presence of ecologically important taxa, including Skeletonema (phytoplankton), Temora (zooplankton), and Arenicola sp. (benthos), underscores the integrity of trophic interactions and the ecosystem's capacity to support marine food webs.

Overall, these findings underscore the importance of sustained environmental monitoring and integrated \sloppy management of anthropogenic inputs from both power plant operations and surrounding human activities. Such measures are essential to maintaining seawater quality and preserving marine biodiversity in coastal areas influenced by industrial development.