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The Correlation Between Coral Cover and The Associated Reef Fishes Abundance in Enggano Island Bengkulu

The coral reef is the habitat for more than a million marine species. The damage of the coral reef could decrease associated marine biodiversity, and the coral reef fishes are one of the groups impacted by the coral reef destruction. This study aimed to measure the coral coverage, to estimate the abundance of coral fishes, and to determine the correlation between coral coverage and abundance of coral reef fishes in Enggano Island, Bengkulu. The line intercept transect method was used by applying 25 m length transects to measure the coral cover in 12 sampling stations. The visual census method was implemented to count the presence of coral reef fishes around the transect line. The correlation between coral coverage and abundance of coral reef fishes was estimated using the multiple-linear-regression method. The results revealed that the coral coverage in Enggano Island varies from 99.6%-6.6%. The highest coverage was observed in station one at the leeward of Dua Island, whereas the lowest was found in station nine at Kahabi. The depth that measured 21 m could cause low coral coverage in condition. The substratum at this depth receives low sunlight intensity; thus, photosynthesis could not function efficiently. The highest coral reef fish abundance estimated at 603 ind/125 m2 was found in station 12 at Berhau, whereas the lowest at 8 ind/125m2 was in station eight at Kahabi. The analysis showed a positive but considerably a weak correlation between coral coverage and abundance of coral reef fishes with an r-value of 0.61 and the determination coefficient of 61.00%.


Introduction
Enggano Island is located in Bengkulu Province; it has a distance of more than 90 miles from the Sumatra mainland. The condition has led to a high illegal fishing activity due to a lack of legal enforcement agents in the area. Consequently, it threats marine ecosystems, including the coral reef, which is typical in the area. The tropical corals are mostly stony coral characterized by a variety of life forms [1]. The coral reef provides shelter for many marine organisms, including coral fishes. An area with high coverage of coral will also have high diversity and abundance of coral fishes [2,3,4].
Coral reef fishes are associated-fishes with the coral reef ecosystem. The coral reef provides habitat and nursery ground for almost all coral reef fishes that create dependencies for the fishes to the coral reef ecosystem. The damage of the coral community will directly affect the existence of associated reef fishes [5,6]. Therefore, coral reef fishes can be used as a bioindicator to measure the health of coral reef ecosystems [7]. The presence or absence of certain types of reef fishes in the coral reef ecosystem is an accurate indication of the health of a coral reef ecosystem. Thus, the decline of coral coverage also has a significant impact on Indonesia's marine biodiversity. Research concerning coral coverage conditions in Enggano Island has recently reported severe damage at the western coast of Enggano Island [8]. An inventory study on the reef fishes also has been completed in the same areas [9]. That recent research has no record on the correlation between coverage of the coral and the abundance of coral reef fishes. Therefore this study aimed to measure the coral coverage, to estimate the abundance of coral fishes, and to determine the correlation between coral coverage and abundance of coral reef fishes in Enggano Island, Bengkulu.

Methods
This study was conducted in April 2018 at Enggano Island of Bengkulu Province, Indonesia. Four dive sites were designated i.e., leward and windward side of Dua Island, Berhau, and Kahabi ( Figure  1). The SCUBA dive was conducted to quantify the coral cover and to tally the coral reef fishes abundance at the 3 to 21 m depth in each location.

Data Collection
The line intercept transect method was used to determine the condition of the coral health based on the coral cover [10]. The roll meter used as 25 m transect was placed parallel to the coastline with three replicates in every dive site. The coral lifeform found along the roll meter was recorded and calculated for the number lifeform and coverage area [10,11]. For the abundance of coral reef fishes, the visual census method was used to count the number within a virtually 2.5 x 2.5 m window on the right and left side of the same line transect [10]. All the fishes found were identified and calculated [12]. The water quality parameters, such as temperature, salinity, visibility, and pH, were measured in situ during the research.

Life forms of coral covers
The life forms of coral and dead coral were calculated based on [10] as follows: is life forms of coral covers, ni is the total length of bottom subtracting (cm), and L is the length of the transect (cm). Furthermore, the category of coral reefs condition was categorized based on Kepmen LH Republic of Indonesia No. 4, Year 2001 (Table 1).

Coral reef fishes Abundance
The abundance of coral reef fishes was calculated based on [13] as follows: Where N is the abundance (Ind/m 2 ), ni is the total of individual fish i, A is an area of the census, and i is replications.

Correlation between Coral coverage and Coral reef fishes abundance
The correlation between coral coverage and abundance of coral reef fishes was analyzed using multiple linier methods in Microsoft excel, where the variable independent (X) was coral coverage and variable dependent (Y) was the abundance of coral fishes.

Coral Coverage
The percentage of coral coverage ranged from 6.6 -96.9 %. The lowest coral coverage was in Kahabi (6.6%) that categorized into severely damage category according to Kepmen

Correlation Between Coral coverage and Coral reef fish Abundance
Based on the correlation analysis between coral coverage and abundance of coral reef fishes showed a positive correlation with r=0.61 and categorized into not a sufficiently strong correlation. Interaction between coral reef fishes and coral reef as its habitat studied by Choat and Bellwood [20].

Coral Coverage
The highest of coral percent cover in Dua Island in Leeward site might be caused by low wave (0.53 m/s). In contrast, a study observing coral reports that live in strong water flow would grow well [1]. Coral coverage more than 30%, and less rubble and sand are categorized into a health condition [16]. The recent study of coral coverage in this location reported coral coverage ranged at 24.02 -49.06 % [8]. It might be coral in this location have been recovered after an earthquake. Furthermore, Kahabi has the lowest coverage of coral than others. The low coral coverage could be caused by depth in Kahabi, which was more than 21 m (Table 2). This depth received low sunlight intensity; thus, photosynthesis could not occur. On the other hand, this location closed to the river that leads to sedimentation.

Coral reef fishes Abundance
The highest abundance of coral reef fishes was found in Berhau. The results of this study are higher than that reported 493 individual/2100 m2 [3]. The presence species Scarus flavipectoralis and Dascyllus aruanus triggered high coral reef fishes abundance in this location. Scarus flavipectoralis and Dascyllus aruanus live schooling and feeding in a coral reef ecosystem. High coral coverage provides a home for nursery, feeding, and spawning ground for many coral fishes [17,18]. Kahabi has the lowest abundance in Enggano island. It might the low coral coverage lead to low fish abundance in this location. Coral reef fishes are one fish that live sedentary in the coral reef. The damaged coral reefs will cause declining coral reef fishes abundance [15]. Kahabi also located in an open water area that has a depth of more than 21 m and utilized by the local community as the fishing ground of fish and sea cucumber.

Figure 2. Correlation Between Coral coverage and Coral reef fish Abundance
Based on the correlation analysis between coral coverage and coral reef fish abundance, it is known as the characteristic distribution of coral fish. Coral reef fishes prefer to associate with a coral reef that has higher coverage than lower. It was shown that Kahabi had low coral coverage, followed by low coral reef fish abundance (Figure 2). There are three interactions between coral reef fishes and coral reefs. Firstly, the coral reef has a function as a nursery ground, feeding ground, and spawning ground. Secondly, there are interactions and associations of organisms associated with a coral reef. Last, there was an interaction of abiotic factors, including environmental conditions and sedimentation. Similar results have been reported in which high fish abundance found in high coral coverage in west Halmahera, west Maluku Province, Indonesia, in contrast to low fish abundance that was found in low coral coverage [15]. This finding shows that the complexity and coral coverage are interrelated with coral reef fishes abundance. The presence of coral reef fishes depends on coral coverage in some areas [19].

Conclusion
Based on the results, Kahabi has the highest prevalence rate compared to other places (7.60%) and the lowest prevalence observed in the windward side of Dua Island (1.22%). This prevalence is classified as not risky for the coral reef ecosystem. Coral coverage in Enggano Island ranged from 6.66% to 99.6%. The highest coverage found in the leeward side of Dua Island (99.6%), and the lowest coverage was in Kahabi (6.6%). The highest coral reef fishes abundance found in Berhau (603 ind/125 m2), and the lowest was in Kahabi (8 ind/125 m2). The correlation analysis showed a positive correlation with r was 0.61, and a determination coefficient of 61%. Multiple linear analysis showed y= 4.9483x -35.942 that indicated there is an increasing the abundance of coral reef fishes for each addition of coral cover.