Advances in Tropical Biodiversity and Environmental Sciences 5(3): 97-102, October, 2021               e-ISSN:2622-0628

DOI: 10.24843/ATBES.v05.i03.p05          Available online at: https://ojs.unud.ac.id/index.php/ATBES/article/view/74422

97

Percentage of Mangrove Canopy Cover and Mollusks Abundance in Benoa Bay Mangrove Ecosystem

Shintani Asri Tinambunan1, Nyoman Dati Pertami 2, and Ni Made Ernawati3

Department of Aquatic Resources Management, Faculty of Marine and Fisheries, Udayana University Jl. Kampus Unud Bukit Jimbaran, Kuta Selatan, Badung, Bali

*Corresponding author: [email protected]

Abstract. This research was conducted to determine the condition of the mangrove ecosystem based on its canopy cover and to determine the types of mollusks (Bivalves and Gastropods) associated with the Benoa Bay mangrove ecosystem. Research on the percentage of mangrove canopy cover is important because it can be used as an indicator in evaluating the growth or damage that exists in the mangrove ecosystem. Research on the abundance of mollusks is important because mollusks have an important role in the function and ecology of the mangrove ecosystem and play a role in the food chain cycle. Hemispherical photography is a method for observing mangrove canopy cover and line transect method for mollusks. The composition of mangrove species found in the research location were five species, namely Rhizophora stylosa, Rhizophora mucronata, Rhizophora apiculata, Bruguiera gymnorrhiza, and Avicennia marina. The percentage of mangrove canopy cover in the Benoa Bay mangrove ecosystem is in a good category (average = 76.59%). There are eight types of mollusks found in the research location consisted of two types of bivalves (Polymesoda bengalensis and Gafrarium pectinatum) and six types of gastropods (Nerita balteata, Nerita picea, Neritina turrita, Pila ampullacea, Cassidula aurisfelis, and Littoraria melanostoma). The relationship between the percentage of mangrove canopy cover and abundance of mollusks in the Benoa Bay mangrove ecosystem has a very low correlation with the correlation value (r = -0.348). The percentage value of mangrove canopy cover did not have a major influence on the abundance of mollusks in the mangrove of Benoa Bay.

Keywords: Benoa Bay; mangrove canopy cover; mollusks.

  • I.    INTRODUCTION

Mangroves are plants that grow influenced by tides and are found along tropical beaches. According to Kusuma (2015). Good mangrove will support the growth and development of associated biota, so it is necessary to protect and supervise the mangrove area so that the mangrove ecosystem is maintained and runs well. One of the areas in Bali Province that has a fairly extensive mangrove is Benoa Bay. Benoa Bay is one of the centers of biodiversity at the ecosystem level in the coastal area of South Bali.

Research on the percentage of mangrove canopy cover is important because it can be used as an indicator in evaluating the growth or damage that exists in the mangrove ecosystem. In the mangrove ecosystem, there are several associated biotas, namely mollusks (gastropods and bivalves). Mollusks have many benefits, namely one of the sources of protein that can be consumed by the community, animal feed ingredients, industrial materials and for medicines (Dibyowati, 2009).

Several studies have been conducted to determine the abundance of mollusks (gastropods and bivalves) in the mangrove ecosystem of the Musi river estuary, Banyuasin

regency, South Sumatera province (Hartoni and Agussalim, 2013) and in the mangrove ecosystem of Gampong Ie Masen, Muara Tiga District,Pidie regency (Ikramullah et al., 2017). Knowing the abundance of mollusks and the relationship between the percentage of mangrove canopy cover is essential as information and is the first step for the Benoa Bay community to manage the abundance of mollusks which have many functions and ecological roles in the mangrove ecosystem.

  • II.    RESEARCH METHOD

Time and Location of the Research

The research was conducted in February 2021 in the mangrove ecosystem of Benoa Bay, Bali. The location of the study was carried out in three stations (Figure1). Station 1 is in the mangrove area around the reservoir (Suwung DAM estuary), station 2 is in the MIC mangrove tourist attraction area and station 3 is between Tukad Mati downstream and Jalan By Pass Ngurah Rai Tuban. Each observation stasiun is expected to represent the mangrove ecosystem of Benoa Bay. The reason for choosing this stasiun is because the mangrove at the location are thick and access to the location is safe.

Figure 1. Map of Sampling Location

Tools and Materials

Tools and materials used in the study can be seen in

  • TABLE 1 below:

TABLE 1

TOOLS AND MATERIALS RESEARCH

No

Tools and Materials

Uses

1

GPS (Global Positioning System)

Determines the position of coordinates at the research location

2

Raffia rope

Makes station line transects

3

Meter

Measuring transect length

4

Stationery

Recording the data found

5

Plastic bag

Sampel container for biota

6

Label paper

Information for biota

7

Alcohol 70 %

Sample preservative

8

Biota identification book

Identifying biota

9

Camera

Research documentation media

10

Filter

Searching for biota

11

Ms. Excel

Processing data

Determination of Sampling Points

The determination of sampling points (three stations) was carried out using the purposive sampling method. Purposive sampling is a sampling method used by conducting considerations or studies first. Each station consists of 3 plots with a size of 10 mx 10 m for mangrove data collection and 3 plots with a size of 1 mx 1 m were selected for mollusks data collection as representatives of mollusks data collection at each station. Observation stations are placed in areas that are not flooded or carried out at low tide.

Data Collection Methods

  • A.    Collecting Mangrove Cover Percentage Data

The method used in collecting data on the percentage of mangrove cover was hemispherical photography and using a camera (Jenning et al., 1999; Korhonen et al., 2006). Furthermore, the method of taking pictures and determining the sampling location followed the guidelines in Dharmawan and Pramudji (2014). The technical implementation is:

  • 1.    Data collection was done using a camera and taking photos is done by being directed perpendicular to the sky. Avoid shooting right next to the trunk of a tree and position the camera at chest height.

  • 2.    Each 10 × 10 m plot is divided into four small plots of 5 × 5 m in size.

  • 3.    There are 4 shooting points on each 10m × 10m plot.

  • 4.    The photo number is recorded on the datasheet form to facilitate data analysis.

  • 5.    Photographs were taken once at each point to prevent confusion in data analysis.

  • B.    Mollusks Data Collection

The collection was carried out using a plot of 1 m × 1m in an area of 10 m ×10 m. Mollusks samples taken were mollusks present in the roots and substrate of mangroves. Data retrieval was carried out at 3 points with the mollusks taking the position, namely the left corner, right corner, and center. Biota collection is carried out directly by hand (hand collecting), then the biota is inserted into a container and labeled with a marker for easy identification. The mollusks was preserved using 70% alcohol and then identified. The mollusks found were then recorded based on the number of individuals and species found at each station.

  • C.    Substrate Sampling

Observation of the type of substrate was done visually (directly) by feeling the texture of the substrate at each station. Then the samples were grouped per station to facilitate data analysis. The types of substrates encountered were mud, sand, and sandy silt.

Data Analysis

  • A.    Mangrove Cover Percentage

The Concept of this analysis is the separation of sky pixels (white color) and vegetation cover (black color) so that the percentage of mangrove vegetation cover pixels can be calculated in binary image analysis (Ishida 2004, Chianucci et al., 2014). Photo analysis using software ImageJ and Microsoft Excel to calculate the percentage of cover. Determination of the level of damage to mangroves is determined based on the regulation of the Ministry of Environment no. 201 of 2004. The standard criteria for mangrove damage can be seen in TABLE 2.

TABLE 2


composition of mangrove species in the Benoa Bay ecosystem can be seen in Figure 2.

CRITERIA FOR MANGROVE DAMAGE

Criteria

Closure (%)

Good        Very Tight

>75

Tight

≥50 - <75

Damage     Rarely

<50

  • B.    Mollusks Abundance

Mollusks Individual abundance refers to the abundance formula, namely:

KI (ind/m2) = ni

Information:

KI     = Species abundance (ind/m2)

Ni      = Number of species species I (ind)

A      = Area of observation (m2)

  • C.    Relationship between Percentage of Mangrove Canopy

Cover and Mollusks Abundance

Data analysis of the relationship between percentage of mangrove canopy cover and mollusk abundance can be determined using a simple regression model with the formula:

Y = a + bx

Description:

Y      = Percentage of Mangrove Canopy Cover

X     = Mollusc Abundance

a      = Constant

b      = Slope

TABLE 3

INTERVAL OF CORREALTION AND LEVEL OF

RELATION BETWEEN FACTORS

No

Interval Coefficient

Level of Relationship

1

0,00 – 0,199

Very Low

2

0,20 – 0,399

Low

3

0,40 – 0,599

Moderate

4

0,60 – 0,799

Strong

5

0,80 – 1,000

Very Strong

III RESULT AND DISCUSSION

  • 3.1    Composition of Mangrove

Species the types of mangroves found during the study were Rhizophora stylosa, Rhizophora mucronata, Rhizophora apiculata, Bruguiera gymnorrhiza and Avicennia marina. The results of the calculation of the

Figure 2. Composition of Mangrove Species

At station 1 and station 3, there were 5 similar types of mangrove, namely Rhizophora stylosa, Rhizophora Mucronata, Rhizophora Apiculata, Bruguiera gymnorrhiza and Avicennia marina. The dominant mangrove species at stations 1 and 3 were the same, namely Bruguiera gymnorrhiza, while at station 2 only Rhizophora mucronata was found. The most dominant type of mangrove found based on the results of the analysis in this study was Rhizophora mucronata. This can be related to the adaptation of habitat conditions that affect the carrying capacity of the community. According to Sani et al., (2019) that Rhizophora spp has fairly good adaptability so that this species easily lives in each area of different environmental types. Agustini et al., (2016) stated that there are four true or dominant plant families in the mangrove ecosystem, namely Rhizophoraceae (Bruguiera, Rhizophora, and Ceriops), Sonneratiaceae (Sonneratia), Avicenniaceae (Avicennia), and Meliaceae (Xylocarpus). Differences in environmental conditions can affect the growing mangrove species.

Percentage of Mangrove Canopy Cover

The percentage value of mangrove canopy cover at the three stations is in the good category according to KEPMEN LH No. 201 of 2004. The results of the percentage of mangrove canopy cover and the condition of the mangrove community in the mangrove ecosystem of Benoa Bay can be seen in TABLE 4.

Nurdiansah and Dharmawan (2018) say that a good percentage of mangrove canopy cover is supported by the value of tree density and suitable environmental conditions can be a factor in a high percentage value. This is supported by the statement of Baksir et al., (2018) that the high percentage value of mangroves is caused by environmental conditions that are suitable for mangrove growth, and low anthropogenic activity in the mangrove

ecosystem will cause the mangrove community to grow densely.

TABLE 4

PERCENTAGE OF MANGROVE COVER AND MANGROVE CONDITION

Station

Dominant Type

Cover

Mangrove (%)

Status

1

Bruguiera gymnorrhiza

78,36

Good

2

Rhizophora Mucronata

74,14

Good

3

Bruguiera gymnorrhiza

77,28

Good

Rata-Rata

76,59

Good

Abundance of Mollusks

  • A.    Abundance of Bivalves

The results of research and identification that have been carried out in the mangrove ecosystem of Benoa Bay, there are 2 species of bivalves, namely Polymesoda bengalensis and Gafrarium pectinatum. The highest species abundance was found at station 1, which was 0.19 ind/m 2. Then at station 2 is 0.08 ind / m2 and the station 3 is 0:03 ind / m2.

Figure 3. Abundance of Bivalves

The highest abundance of bivalves was found at station 1, this is supported by the higher percentage value of mangrove canopy cover at station 1, namely 78.36%. According to Putri (2021) that if the mangrove density is high, the presence of bivalves in the ecosystem is high, but the difference in the value of bivalves density at each station is also caused by the non-selective catching factor of bivalves by the surrounding community. Then Arbi (2012) states that the high and low value of the uniformity index of a species is caused by several factors, namely the number of species or species obtained, the number of individuals obtained exceeds the number of other

individuals, then the homogeneity of the substrate and habitat conditions in the ecosystem.

  • B.    Abundance of Gastropod

There were six spesies of gatropods found, namely Nerita balteata, Nerita picea, Neritina turrita, Pila ampullacea, Cassidula aurisfelis and Littoraria melanostoma. The highest abundance of gastropods was found at station 1 which was 121 ind/m2, while the lowest abundance value was found at station 2 which was 0.50 ind/m2 and at station 3 which was 0.89 ind/m2.

  • Figure 4. Abundance of Gastropods

According to Kusrini (2000), gastropod species are generally more commonly found in mangrove ecosystems with species Avicennia marina, Rhizophora mucronata, and Rhizophora stylosa. This can be related to the number of gastropods found in each station. At station 3, only 1 mangrove species was found, namely Rhizophora mucronata, so it is suspected that this affected the number of gastropods found to be less than at stations 1 and 3. Riniatsih and Wibowo (2009) stated that Neritidae is a biota that prefers a slightly muddy sand substrate in tidal areas, but at the time of the study, the type of substrate obtained was muddy.

Correlation of Percentage of Mangrove Canopy Cover with Mollusc Abundance in Benoa Bay Mangrove Ecosystem

The correlation value (r) of the relationship between the percentage of mangrove canopy cover and abundance of mollusks in the mangrove ecosystem of Benoa Bay is very low, which means that the percentage of mangrove canopy cover does not have a major influence on the abundance of mollusks in the Benoa Bay mangrove ecosystem.

Figure 5. Relationship between Percentage of Mangrove Canopy Cover with Mollusks Abundance in the Mangrove Ecosystem of Benoa Bay

The abundance of mollusks in the mangrove ecosystem of Benoa Bay is thought to be influenced by several factors, namely food availability, predation and competition between species. In the study of mangrove density and gastropod abundance in the mangrove and proboscis monkey conservation are (KKMB) OF Tarakan city (Gazali et al., 2019) that the correlation value obtained was 0,4766 including a suffivient correlation. The abundance of gastropods at the study site was influenced by other variables such as sediment, organic matter and the abailability of sunlight.

  • IV. CONCLUSION

The percentage of mangrove canopy cover in the Benoa Bay mangrove ecosystem is in good category with an average value of 76.59%. Mollusks found in mangrove ecosystem of Benoa Bay consisted of eight species from two classes, namely the bivalves class consisting of two species, namely Polymesoda bengalensis and Gafrarium pectinatum, and the gastropod class consisting of six species, namely Nerita balteata, Nerita picea, Neritina turrita, Pila ampullacea, Cassidula aurisfelis, and Littoraria melanostoma. The relationship between the percentage of mangrove canopy cover and the abundance of mollusks in the Benoa Bay mangrove ecosystem has a very low correlation (r = -0.348). The percentage value of mangrove canopy cover did not have a major influence on the abundance of mollusks in the mangrove ecosystem of Benoa Bay.

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