Coral Reef Diversity and Habitat Characteristics in the Waters of Nasi Island, Aceh Province, Indonesia

Nasi Island is one of the outermost small islands in Aceh Province, directly connected to the Indian Ocean and the Andaman Sea [1]. Administratively, this area is recognized as the zero point of Indonesia in the western region [2]. Nasi Island is situated far from the provincial and district capitals, separated by the sea. Transportation for the local community generally relies on water transport, such as boats and ships. The Indo-Pacific region, including this area, is renowned for its high coral reef diversity and remarkable ecological complexity [3]. Coral reef ecosystems play a vital role in maintaining the physical, ecological, and economic stability of the surrounding area [4].

Corals are benthic marine organisms belonging to the class Anthozoa, classified under the Phylum Coelenterata or Phylum Cnidaria. These corals exhibit a wide variety of forms and unique, vibrant colors. Morphologically, corals are often found with branching structures, mushroom-like shapes, or forms resembling musical instruments [5]. Various coral species predominantly inhabit the seabed of oceans, straits, and even the ocean floor. These organisms are classified as benthos, thriving on the seabed, and are widely found in the Indian Ocean, Atlantic Ocean, and Pacific Ocean [6]. Generally, corals exhibit a colonial life characteristic in marine habitats, although certain species are also found living solitarily [7].

Corals are known as a group of benthic organisms with highly specific habitat characteristics in marine waters. These marine organisms thrive and grow optimally under conditions of water salinity ranging from 33‰ to 36‰, with high dissolved oxygen levels reaching 13.73 ppm [8]. They live by attaching themselves to the seabed, such as rocks or hard substrates, as an adaptation to withstand wave action [9]. Coral reef ecosystems serve as the fundamental foundation for marine life, playing a crucial role in marine areas as habitats for various aquatic species, including Pisces, Crustaceans, Mollusks, and Plankton [10, 11]. These ecosystems are recognized as areas with the highest biodiversity in the world due to their roles as protective zones, spawning grounds, rich food sources, and their complex food chains [12]. More than 25% of various flora and fauna species in coastal areas, directly or indirectly, depend on coral reef ecosystems. Additionally, these ecosystems support the growth and development of seagrass beds and mangrove vegetation in adjacent areas [13].

Coral reef ecosystems play a vital role in the food chain system within marine waters. A higher level of coral diversity indicates the complexity of the marine environment, as coral reef ecosystems serve as habitats for various species of Pisces, Crustacea, Gastropoda, Bivalvia, and other aquatic species [14, 15]. Coral reef ecosystems also function as spawning grounds, nursery areas, and protective zones for various aquatic organisms against marine predators [16]. If coral reef ecosystems are not well-preserved in a marine area, it will lead to a decline in the populations of various aquatic organisms within that area [17].

Research conducted in the waters of Aceh Province indicates that coral reef ecosystems have suffered damage ranging from moderate to severe. The primary cause of this damage is human activity, particularly the use of water transportation and the operations of boats and fishing vessels, including their docking along the coastline [18]. Conservation efforts are among the most effective solutions for preserving coral reef ecosystems in their natural marine habitats. However, there is a significant lack of information regarding the population and diversity of corals in the waters of Aceh Province.

This study aims to assess coral species diversity and identify environmental drivers influencing coral distribution in Nasi Island’s neritic waters. Research to examine coral diversity in the neritic zone waters around Nasi Island is crucial, given the vital role coral reef ecosystems play in marine environments as habitats for various aquatic biota, which local communities rely on for their daily livelihoods. Coral diversity in a marine area can serve as an initial indicator of the condition of the marine environment, whether it remains in good condition or is subject to mild to severe pollution. Data on coral diversity can also serve as a reference for communities and governments in managing coastal and marine areas to ensure sustainability and support the livelihoods of coastal communities.

The research results in the waters of Nasi Island in the neritic zone successfully collected 32 coral species (Figure 2) from 6 families (Figure 3). Acroporidae was the family with the highest number of species in the study area, while Euphylliidae had the lowest number of species collected at the research location (Table 2).

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Figure 2. Coral species collected at the research location

1. Acropora clathrata (Brook, 1891), 2. Acropora intermedia (Brook, 1891), 3. Acropora millepora (Ehrenberg, 1834), 4. Acropora Robusta (Dana, 1846), 5. Acropora rudis (Rehberg, 1892), 6. Dipsastraea lizardensis (Veron, Pichon & Wijsman-Best, 1977), 7. Dipsastraea favus (Forskål, 1775) , 8. Favites halicora (Ehrenberg, 1834), 9. Acropora tenuis (Dana, 1846), 10. Heliofungia actiniformis (Quoy & Gaimard, 1833), 11. Lobactis scutaria (Lamarck, 1801), 12. Galaxea astreata (Lamarck, 1816), 13. Galaxea fascicularis (Linnaeus, 1767), 14. Goniopora lobata (Reuss, 1864), 15. Hydnophora microconos (Lamarck, 1816), 16. Pleuractis paumotensis (Stutchbury, 1833), 17. Montipora danae (Milne Edwards & Haime, 1851), 18. Montipora foliosa (Pallas, 1766), 19. Montipora informis (Bernard, 1897), 20. Astrea annuligera (Milne Edwards & Haime, 1849), 21. Platygyra daedalea (Ellis & Solander, 1786), 22. Platygyra pini (Chevalier, 1975), 23. Platygyra sinensis (Milne Edwards & Haime, 1849), 24. Pocillopora damicornis (Linnaeus, 1758), 25. Pocillopora verrucosa (Ellis & Solander, 1786), 26. Porites cylindrica (Dana, 1846), 27. Porites lobata (Dana, 1846), 28. Porites lutea (Milne Edwards & Haime, 1851), 29. Porites mayeri (Vaughan, 1918), 30. Seriatopora caliendrum (Ehrenberg, 1834), 31. Seriatopora hystrix (Dana, 1846), 32. Seriatopora pistillata (Esper, 1792)

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Figure 3. Distribution of coral families and species at the research location

Table 2. Number of coral families and species by research location

In general, the distribution of corals in the study area shows that the Acroporidae family is the most prevalent, accounting for 28.1% of the samples, while the Euphylliidae family is the least found at 6.2% (Figure 4). The habitat characteristics and the ability to adapt to the conditions of the neritic zone, which are disturbed by the activities of local fishing boats and vessels using water transportation, influence the life of various aquatic organisms, including the coral reef ecosystem.

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Figure 4. Percentage of coral families in the study area

The characteristics of habitat and the abundance of food sources in a marine area have a significant impact on the abundance of coral species and families living in a particular area. Species from the Acroporidae family were the most dominant across all three research locations, with this family accounting for up to 50% of the corals collected in the Dedap area. The Fungiidae family had the lowest number of species found in the research locations, and no species from the Fungiidae family were found in the Alue Riyeung area (Figure 5).

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Figure 5. Percentage composition of corals based on species and family

Based on the research results from the three study locations, the highest number of species was collected in the waters of Pasie Janeung, with 24 coral species out of a total of 32 species overall. In contrast, the lowest number of species was collected in the waters of Dedap, with only 12 coral species. Across all three research locations, the same number of coral families was found, with each location having 5 coral families (Figure 6).

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Figure 6. Number of coral families and species by research location

Based on the analysis of the diversity index in the waters of Nasi Island, the coral diversity varies significantly between locations. However, all three locations still fall within the moderate diversity index category. The waters of Pasie Janeung exhibited the highest diversity index with a value of H' = 2.97, nearly reaching 3. The lowest diversity index was found in the waters of Dedap, with a value of H' = 2.26. The coral dominance index in the three research locations ranged from 0.06 to 0.12, which is considered low. The highest dominance index was found at the Dedap and Alue Riyeung locations, while the lowest was at Pasie Janeung (Table 3).

Table 3. Coral diversity index (H') and coral dominance index (D) at the research locations

The analysis of species richness and evenness of coral reefs at the research sites revealed differences in species richness among the three locations. However, all remained within the same category, namely, low. Similarly, the evenness index of coral reefs varied across locations, but consistently fell into the high category, indicating that the coral reef communities at the study sites are still stable. The detailed data on coral reef species richness and evenness at the research sites are presented in Table 4.

Table 4. Species richness and evenness of coral reefs

3.1 The relationship between physical and chemical environmental parameters and coral diversity

The measurement of environmental parameters at the study sites revealed variations across the three locations. The highest water salinity was recorded at Pasie Janeng, ranging from 34.5‰ to 35.5‰, while the lowest was observed at Dedap, ranging from 31‰ to 33‰. Similarly, dissolved oxygen levels were highest at Pasie Janeng and lowest at Dedap. The detailed environmental parameters are presented in Table 5.

Table 5. Environmental parameters at the study sites

Principal Component Analysis (PCA) analysis shows a strong relationship between coral diversity in the study locations and several physical and chemical environmental parameters. The neritic zone of Pasie Janeung exhibits the highest coral diversity, which is strongly correlated with water temperature, dissolved oxygen, salinity, and pH levels. This is evidenced by the proximity of these environmental parameters' axes to the Pasie Janeung location in the PCA plot (Figure 7).

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Figure 7. Relationship between physical and chemical environmental parameters and coral diversity

The research successfully collected 32 coral species belonging to 6 families. The coral diversity index at the research locations ranged from 2.26 to 2.97, which falls under the moderate category. The Pasie Janeung location exhibited the highest coral diversity compared to the other two locations, while the lowest diversity was found at the Dedap location. Suitable habitat characteristics, such as water temperature, dissolved oxygen, salinity, and pH levels, have a strong correlation with coral diversity at the study locations. The use of water transportation, such as boats and fishing vessels, for fishing and docking is one of the factors contributing to the decline of the coral reef ecosystem in the Dedap and Alue Riyeung areas. The importance of local wisdom-based conservation efforts to maintain the sustainability of coral reefs in a sustainable manner, considering that coral reef ecosystems are the habitat of various marine fishery animals, as a livelihood for fishermen.