Mangrove Health Assessment Using Hemispherical Photography: A Case Study on Mangrove Ecosystem for Ecotourism at Tajungan-Bangkalan, Madura Island, Indonesia

Abstract

Mangrove health status indicates sustainable management and efforts to control forest damage. The hemispherical photographic method facilitates the observation and monitoring of forest health. This method is also more accessible, faster, and practical than the conventional method. Data analysis in this method requires Image J software. The selection of research sites aims to determine forest management for mangrove ecotourism. Thus, rehabilitation decision-making is right on target. The research results on the health status of mangroves in Tajungan-Bangkalan, Madura Island, Indonesia, showed moderate-to-good levels. The percentage of cover in the good category is at the MDRT01 station, which is 81.64 ± 3.35%. The MDRT02 observation station has a closing percentage of 64.31% ± 20.41% and is in the moderate category. The suitability of tourism based on the percentage of closure is in the appropriate category at the MDRT02 station and very suitable at the MDRT01 station. The results of this study could be used for planning of mangrove ecotourism and also for education on planting of mangrove seedlings.

1. Introduction

Mangrove forest is a coastal ecosystem with a critical ecological role in the shallow water zone. This collection of vegetation forms an ecosystem with environmental services producing nutrients for aquatic organisms, helping the carbon cycle, and protecting organisms and the coastal environment. In addition, mangrove ecosystems have benefits that are currently developing as conservation, rehabilitation, and educational areas to increase community welfare [1, 2, 3].

Coastal development, expansion of aquaculture, overfishing, and climate change threaten the existence of mangroves worldwide. As a result, the mangrove forest area decreased by 62% between 2000 and 2016 [4]. Research into the causes of mangrove loss over the last 20 years reveals that socioeconomic and biophysical factors account for most of the degradation, despite increasing mangrove cover in some areas [5].

A decline in the quantity and quality of mangrove forests has also occurred in Indonesia, particularly in Tajungan Village, Kamal District, Bangkalan Regency on Madura Island. The mangrove ecosystem in Tajungan Village is an area that controls coastal conditions from the threat of abrasion, land subsidence, and seawater intrusion. Cultivated land, housing, and others have changed the mangrove area through logging/deforestation. Preliminary observations in the field noted problems in managing mangrove ecosystems in Tajungan Village, Kamal District, Bangkalan Regency, based on environmental conditions, including tree felling, beach abrasion, garbage, and damage caused by local communities. This problem causes a decrease in the environmental quality of the mangrove ecosystem in this area. In addition, the technical problems in managing this mangrove ecosystem are the limited human resources in terms of numbers, education, management experience, service, and supervision.

One of the efforts to utilize and preserve mangrove ecosystems is through ecotourism activities. Appropriate and environment-based planning and management of coastal areas are necessary to protect the sustainability of mangrove ecosystems from achieving sustainable regional development [6, 7]. One of the efforts made by the village of Tajungan is the development of mangrove ecotourism as a conservation and educational effort.

The basic principle of ecotourism is to enhance conservation. However, few studies have assessed their effectiveness in meeting conservation objectives and whether the type of tourism activity affects outcomes. Small-scale tourist sites have more considerable social conservation outcomes, including conservation ethics, perceptions, attitudes, and behavior changes. The type of tourism, and the associated incentives, can significantly affect conservation outcomes [8]. The coastal ecotourism that is currently developing is mangrove ecotourism. One of the best opportunities is to ensure that mangrove-based tourism is carried out based on sustainable principles [9]. One of the criteria for due diligence on mangrove ecotourism is the percentage of forest cover [10, 11]. This closure percentage can also indicate the health of the mangrove ecosystem [12]. Using the hemispherical photography method, the mangrove health assessment technique based on the percentage of mangrove cover produces more accurate data with easy application. This technique uses a camera with a viewing angle of 180 degrees at one point of capture [13, 14]. The definition of canopy cover percentage is the vertically projected portion of the land surface that is overgrown with plants [13]. The result is the percentage of community canopy cover, which is one of the main components of the Mangrove Health Index (MHI) [15]. Current research rarely discusses mangrove ecotourism in Indonesia and its relation to health status. Therefore, this study aims to assess the health status of mangroves based on the percentage canopy cover and their suitability for tourism areas. The result of this research helps ensure the preservation of the mangrove ecosystem as a tourism resource in Tajungan Village.

2. Method

2.1 Stations and observation plots

This research was conducted in Tajungan Village, Kamal District, Bangkalan Regency, East Java, Indonesia. The research locations are presented in Figure 1 and Table 1.

Figure 1.

Station and observation plots.

No	Station/plot	Coordinate
1	MDRT01
	MDRT01_01	S 07.15586E 112.69589
	MDRT01_02	S 07.15592E 112.69598
	MDRT01_03	S 07.15596E 112.69603
2	MDRT02
	MDRT02_01	S 07.15584E 112.69600
	MDRT02_02	S 07.15592E 112.69598

Table 1.

Station locations and observation plots.

2.2 Research methods

2.2.1 Identification of potential station points

The step to determine the observation station (To) begins with the interpretation of mangrove objects, namely identifying the distribution of mangroves in regional stations using Google Earth which provides an initial spatial picture of the existence of mangrove ecosystems. The determination of the number of stations takes into account regional representation, time availability, resources, and budget. Subsequently, potential stations were created as candidates for permanent monitoring sites and required verification for inclusion on a provisional thematic map. After the establishment of permanent monitoring plots, species identification was carried out based on Tomlinson’s [16] reference. If there are doubts about the identification, the researcher takes photos of the parts of the mangrove plant, namely stands, roots, stems, leaves, flowers, fruit, and samples, for further identification in the laboratory with the help of literature or the help of mangrove identification experts. Researchers must record all data obtained using worksheets on waterproof paper.

2.2.2 Data collection

This study used the line transect method by making the plots perpendicular to the coast toward the land. Placement of plots is by using stratified random sampling in each stratum by considering the ease of access to the observation sites.

The number of research stations is two, with each station consisting of three and two2 plots, so there are five plots in this study. Observation plots were made parallel to the coastline, measuring 10 × 10 m² using a rolling meter and surrounded by rope.

2.2.3 Cover percentage

Collecting mangrove cover percentage data follows the steps of collecting mangrove community data. Analysis of the percentage of mangrove cover uses the hemispherical photography method, which requires a camera with a viewing angle of 180 degrees at one shooting point [13, 14]. This technique tends to be relatively new in Indonesia with its application to mangrove forests. The photos taken in this study used a 24 MP smartphone front camera with 1:1 frame mode. However, implementing this method is very easy and produces more accurate data. The steps for implementing this method are that each plot measuring 10 × 10 m² is divided into four (four) quadrants measuring 5 × 5 m². The firing points are around the center of the small square; they had to get between one tree and another and avoid shooting right under the tree trunk. The position of the camera is parallel to the chest height of the researcher/team who took the photo and is perpendicular/facing straight to the sky. Photo numbers are recorded on a data sheet form to simplify and speed up data analysis. Minimum shooting is done at four quadrant points with each plot measuring 10 × 10 m², without repeating and marking photos at the end of each shooting session in each plot. Taking photos in this study at least 20 points with the assumption that there are five plots, and each plot has four quadrants of shooting points. When shooting avoid taking multiple photos at each point to prevent confusion in data analysis [17]. Figures 2 and 3 present illustrations of taking photos of mangrove cover.

Figure 2.

(a) Illustration of the hemispherical photography method for measuring mangrove cover [13, 14]; (b) the results of shooting using a fisheye lens vertically [17].

Figure 3.

Shooting points in each observation plot [17].

2.3 Data analysis

The analysis of percentage cover data was done using Image J software by separating sky pixels and vegetation cover. Converting a photo to 8 bits is the first step to separate the canopy and sky into a single color line, namely from white (0) to black (255). Next, calculate the number of pixels of the sky (white) and canopy (black) in the histogram menu of the Image J software. Finally, the percentage of canopy cover is the ratio of the number of pixels of the canopy (P₂₅₅) divided by the total number of pixels (P_tot) multiplied by 100% for each observation photo (Eq. (2)):

$${\mathrm{P}}_{255}=P_{\mathrm{tot}}-P_0$$E1

$$C=\frac{P_{255}}{P_{\mathit{tot}}}\times 100\%$$E2

Information:

1. C = percentage of canopy cover (%)

2. P₂₅₅ = the number of pixels with a value of 255 (canopy).

3. P₀ = the number of pixels with a value of 0 (sky)

4. P_tot = the total number of photo pixels

2.4 Interpretation of results and determination of mangrove community conditions

The analysis results will produce a density value in units of trees/ha and the percentage of cover in percent units (%). These results can describe the status of the condition of mangrove forests which are categorized based on the Decree of the Minister of Environment No. 201 of 2004, as presented in Table 2.

Criteria	Cover (%)
Good	≥75
Moderate	50–75
Damage	<50

Table 2.

The standard for damage to mangrove forests based on the decree of the minister of environment No. 201 of 2004.

3. Results and discussion

Observation of the mangrove community in Tajungan Village, Kamal District, Bangkalan Regency, East Java, was carried out at two locations designated as stations, namely MDRT 01 and MDRT 02. The mangrove forest ecosystem in the study area consisted of seven species spread across observation stations, namely Avicennia marina, Avicennia alba, Avicennia officinalis, Avicennia rumphiana, Sonneratia alba, Rhizophora mucronata, and Rhizophora apiculata (Table 3). The mangrove forests in the study area have varied types and conditions with a slightly sandy mud substrate. In addition, solid anthropogenic waste covers 40% of the observed area of the mangrove ecosystem at this location.

No	Station	Species
1	MDRT01	Avecennia marina; Rhizopora apiculata; Rhizopora mucronata; Sonneratia alba
2	MDRT02	Avecennia marina; Avecennia alba; Avecennia officinalis; Avicennia rumphiana; Sonneratia alba

Table 3.

The species of mangrove species at each station.

The process of analyzing the percentage of mangrove forest cover is shown in Figure 4. After separating the photo into two colors, calculate the number of pixels using the histogram menu on the analysis tab (Figure 5). This mode displays the number of black-and-white pixels.

Figure 4.

(a) Photos opened using image-J, and (b) photos that have been converted to 8-bit image.

Figure 5.

The histogram shows that the analyzed photos have almost 24 million pixels (count), dominated by canopy pixels (255) with 20,102,188 black pixels.

The results of taking photos of the canopy cover using the hemispherical photography method and analysis using the Image J software structure in Tajungan Village, Kamal District, Bangkalan Regency, East Java, are presented in the following. The percentage of canopy closure for each station is the average of all plots in Table 4. The percentage of canopy closure by category of mangrove damage is presented in Table 5.

Quadrant	Cover canopy (%)
	Plot 1	Plot 2	Plot 3
MDRT01
1	76.16	78.65	83.56
2	86.95	66.75	82.26
3	82.76	81.29	87.05
4	79.12	73.62	84.39
5	84.57	80.83	86.99
6		78.51
7		88.43
8		75.55
9		79.80
Average	81.91	78.16	84.85
MDRT02
1	16.65	85.96
2	32.12	76.58
3	44.11	76.26
4	86.40	68.17
5	70.10	86.75
Average	49.88	78.74

Table 4.

The results of hemispherical photography photo analysis using Image-J software.

No	Station	Canopy cover (%)	Category
1	MDRT01	81.64 ± 3.35	Good
2	MDRT02	64.31 ± 20.41	Moderate

Table 5.

Canopy cover percentage and damage categories.

The analysis results show that the highest percentage of canopy cover is at station MDRT01 (81.64%) and station MDRT02 (64.31%). The status of mangrove damage refers to Minister of Environment Decree Number 201 of 2004 concerning standard criteria and guidelines for determining mangrove damage. Based on the percentage canopy cover, the mangrove ecosystem in Tajungan Village, Kamal District, Bangkalan Regency is in the moderate-to-good category. The amount of mangrove ecosystem canopy cover at each station and the average cover, along with the standard deviation, can be seen in Figure 6.

Figure 6.

The average percentage of cover and standard deviation at each observation station.

As one of the suitability criteria for mangrove ecotourism in the research area, mangrove cover is in the appropriate category at the MDRT02 station and very suitable at the MDRT01 station. The category corresponds to the 50–75% coverage range and is very suitable in the >75% range [10]. The higher the percentage of mangrove canopy cover, the higher the level of health and suitability for ecotourism.

The tree canopy functions like an umbrella, dividing and breaking the penetration of sunlight and rain. Dominant mangrove species affect the percentage of mangrove canopy cover. Areas dominated by Rhizophora sp. with broad leaf morphology had a more significant percentage of canopy cover than areas dominated by mangrove species with small leaves. Stem diameter, density, and tree height also determine the level of mangrove canopy cover [18]. Global trends show that rainfall, temperature, cyclone frequency, and other geophysical factors that affect the maximum mangrove canopy height by 74% on a local and regional scale [19]. In addition, environmental damage due to sea waves, sunlight levels, and predation can affect the formation of mangrove canopy cover [16]. The large tree diameter with high-density supports canopy cover, influencing the mangrove cover percentage. Mangrove canopy cover can show the natural level of mangrove ecosystems and detect anthropogenic threats [17]. In addition, the tree density value supports the mangrove cover’s relatively good condition [20]. Based on this, tree categories’ density and environmental characteristics’ suitability generally affect the percentage of mangrove canopy cover [20, 21]. The results of this study can be used as a guide in developing educational ecotourism planting mangrove seedlings.

4. Conclusions

1. Analysis of canopy cover in the mangrove ecosystem in Tajungan Village, Kamal District, Bangkalan Regency, using the hemispherical photography method, shows that the highest percentage of canopy cover is at the MDRT01 station (81.64%) with the good category and the MDRT02 station (64.31%) with the moderate category.

2. The suitability of tourism for the percentage of cover category is in the appropriate category at the MDRT02 station and very suitable at the MDRT01 station.