Macrozoobenthos are demersal organisms that are sedentary and have slow movements, making them highly susceptible to environmental conditions (Minggawati, 2013). Due to this sensitivity, macrozoobenthos are frequently used as bioindicators for assessing water quality (Dabrowska et al., 2016; Rosdatina et al., 2019; Ramadhaniaty et al., 2021). These species play an important role in the aquatic ecosystems as decomposers (Desmawati et al., 2020; Kumar et al., 2013) and transfer energy to the next trophic levels as prey for other aquatic animals such as fish and water birds (Ridwan et al., 2016; Jędruch et al., 2019).
In Indonesia, several groups of macrozoobenthos, particularly bivalves and gastropods, are used as protein sources by local communities and are traded in local markets. However, these species have been intensively harvested without regard to size, leading to overharvesting and diminishing wild stocks (Almohdar et al., 2017; Aralaha et al., 2015; Sarong et al., 2015). Overharvesting can cause population stress, leading to premature spawning to maintain their population (De Jong et al., 2015). This can affect the stability of the water ecosystem and reduce water productivity.
Studies on the diversity of macrozoobenthos have been carried out in Indonesia waters, for example, Irham et al. (2022) examined the abundance and diversity of the benthic community in Krueng Cut estuary Banda Aceh, and they recorded seven species of benthos with low diversity and moderate dominance indices. Furthermore, Octavina et al. (2018) reported seven species of macrozoobenthos in Gosong Telaga Aceh Singkil with a moderate diversity index. The biodiversity and community composition of freshwater and marine macrozoobenthos in the waters of Gonrontalo were analyzed by Kadim et al. (2022); they concluded that the diversity of macrozoobenthos in these waters was low to moderate. However, in Aceh province, specifically in the southwest coast regions, there is a lack of exploration and reports. Currently, there are only two reports available from this region. The first report was by Munandar et al. (2016) who studied macrozoobenthos diversity in the Kuala Rigaih estuary, Setia Bakti District. Aceh Jaya District recorded 10 species from this estuary. The second report by Rizka et al. (2016) examined macrozoobenthos diversity on the coast of Nagan Raya and concluded that the diversity of these species in the area tends to be moderate, indicating unstable water condition (Rizka et al., 2016). Therefore, the above studies indicate that the diversity of macrozoobenthos in Indonesian waters ranges from low to moderate. This is an indication of a general problem with the quality of water in Indonesia.
The Rasian River and the Asahan River are located in the Pasie Raja and Kluet Selatan subdistricts, Aceh Selatan District in Aceh province, Indonesia. Both traditional and illegal mining activities, such as traditional sand and gold mining, are carried out in this district and the local government has planned to develop the cement industry in this area. Therefore, in this study, we aimed to document the diversity of species and distribution of macrozoobenthos in the Rasian and Asahan rivers and to examine the heavy metal contamination in one of the dominant species of macrozoobenthos,
Sampling was carried out in the estuary of Rasian and Asahan rivers of Aceh Selatan district, Aceh province, Indonesia, in July 2022. In each estuary location, three sampling points were determined randomly (Figure 1). The scenery of the two estuary locations is shown in Figure 2.
Macrozoobenthos were collected on a 1 m × 1 m squared transect. At each sampling point, substrate samples from a depth of about 20 cm were taken with a shovel and then sieved with a mesh size of 0.5 mm. The macrozoobenthos samples were placed in a plastic bag, and then preserved with 10% formalin and transported to the Marine Biology Laboratory, Faculty of Marine and Fisheries, Universitas Syiah Kuala for identification based on Wye (1992) and Compagno (1998).
The macrozoobenthos density was calculated according to Brower et al. (1977) as follows:
The Shannon–Wiener diversity index (H') was calculated based on Krebs (1989) as follows:
The uniformity index (E) was calculated based on Krebs (1989) as follows:
Simpson dominance index was calculated based on Odum (1996) as follows:
Analysis of heavy metals was carried out in the predominant macrozoobenthos in the two rivers, which was
The data were presented in tables and figures and then analyzed descriptively by comparing them with relevant previous studies or reports.
The Rasian River estuary contained 14 species of macrozoobenthos, while the Asahan River estuary contained seven species, resulting in a total of 17 across both rivers (Table 1). These species belonged to two phyla (Mollusk and Arthropoda) and three classes (Bivalvia, Gastropods, and Crustaceans). The external morphology of the macrozoobenthos found during the survey is presented in Figure 3. Analysis of the density of macrozoobenthos in the Rasian River showed that
Composition of macrozoobenthos in the Rasian and Asahan river estuaries
Tabelle 1. Die Zusammensetzung des Makrozoobenthos in den Flussmündungen Rasian und Asahan
Mollusk | Bivalvia | Donacidae | √ | √ | |
Donacidae | √ | - | |||
- | √ | ||||
Ostreidae | √ | √ | |||
Gastropoda | Terebridae | √ | - | ||
Neritidae | √ | √ | |||
√ | - | ||||
Pachychillidae | √ | √ | |||
Planaxidae | √ | - | |||
Potaminidae | √ | - | |||
- | √ | ||||
Trochidae | √ | - | |||
Arthropoda | Malacostraca | Ocypodidae | √ | - | |
Hippidae | √ | - | |||
Eriphiidae | √ | - | |||
Portunidae | √ | - | |||
Total | Decapoda | - | √ | ||
14 | 17 | 14 | 7 |
Note: RRE = Rasian River estuary, ARE = Asahan River estuary, √ = present, - = absent
Density, diversity, uniformity, and dominance indices of macrozoobenthos in the Rasian and Asahan rivers
Tabelle 2. Dichte-, Diversitäts-, Uniformitäts- und Dominanzindizes von Makrozoobenthos in den Flüssen Rasian und Asahan
Location | Species | Density (ind./m2) | Diversity index (H′) | Uniformity index (E) | Dominance index (C) |
---|---|---|---|---|---|
Rasian River estuary | 3.67 | 2.24 (Moderate) | 0.84 (High) | 0.14 (No dominant species) | |
5.00 | |||||
1.67 | |||||
0.67 | |||||
2.00 | |||||
7.33 | |||||
2.33 | |||||
13.33 | |||||
1.00 | |||||
0.67 | |||||
3.67 | |||||
0.67 | |||||
4.00 | |||||
1.00 | |||||
Asahan River estuary | 88.3 | 1.05 (Moderate) | 0.54 (Moderate) | 0.43 (No dominant species) | |
1.7 | |||||
2.3 | |||||
162.0 | |||||
9.3 | |||||
18.7 | |||||
0.3 |
Heavy metal analysis in the
The average concentration of heavy metals Hg, Cd, and Pb in the Funus ater sample collected from Rasian River and Asahan River estuaries
Tabelle 3. Die durchschnittliche Konzentration der Schwermetalle Hg, Cd und Pb in der Funus ater-Probe, die aus den Flussmündungen Rasian River und Asahan River entnommen wurde.
1. | Mercury (Hg) | % | AAS | 0.001 | 0.0845 | 0.1115 |
2. | Cadmium (Cd) | % | AAS | 0.001 | 0.0002 | 0.0002 |
3. | Lead (Pb) | % | AAS | 0.008 | 0.0005 | 0.0005 |
Note: RRE = Rasian River estuary, ARE = Asahan River estuary
Based on the degree of the Minister of State for the Environment, Republic of Indonesia, No. 51 of the year 2004.
The species diversity index of macrozoobenthos in the Rasian and Asahan rivers was in the moderate category, but the value was lower compared to those reported in several related studies in the area, for instance, in the Peat Swamp forest in Nagan Raya and Aceh Barat Daya districts (Riska et al., 2016) and in Kuala Rigah, Setia Bakti Subdistrict, Aceh Jaya District (Munandar et al., 2016). In general, the number of macrozoobenthos species in the Rasian River was higher than in the Asahan River; this may be due to the sampling area in the Rasian River having diverse sediment characteristics and being predominantly muddy and adjacent to mangrove ecosystems dominated by nipah (
A total of 17 species of macrozoobenthos were recorded, of which 14 were found in the Rasian estuary and seven in the Asahan estuary, and therefore, the Rasian River estuary has a high diversity. However, a large number of individuals were encountered in the Asahan estuary. The diversity index of macrozoobenthos in both estuaries was in the moderate category. In addition,